Ever eaten cold leftover rice? Then you, like so many of us, have the imperishable sense memory of retrogradation, the way the grains rattle as you scoop them and grind grittily between your teeth.

Starch—the delicious form in which many plants store energy—is composed of microscopic round granules, each of which contains two kinds of starch molecules: amylose and amylopectin, with somewhat different properties. Amylose is a long, chain-shaped molecule, and amylopectin is a bushy, branching molecule. The characteristics of different starches—the difference between waxy potatoes and floury potatoes, for example—are often due to their differing ratios of amylose to amylopectin, as well as the size of their starch granules.

When starchy foods—rice, pasta, bread dough—are cooked in the presence of water, all those individual granules of starch absorb water and swell up. The amylose and amylopectin molecules in the granules, formerly clinging together, relax a bit and come apart, allowing water to seep in among them. This causes the food to become softer and more digestible, as the starch and water form a gel. This process is called gelation. (It’s often called gelatinization instead, which makes it sound like there’s gelatin involved. There’s not, just starch and water.) Amylopectin gelates at a lower temperature than amylose, and swells up more, because the molecule’s shape allows it to take in a lot more water.

So, say you’ve made a delicious, fluffy, steamy batch of long-grain rice. Long-grain varieties of rice tend to cook up separate and fluffy, because their starch contains a higher percentage of amylose, which means the granules tend to stay more intact as they swell. When shorter-grain rice cooks, its bushy amylopectin swells up a lot, starting at a lower temperature—earlier in the cooking—and ruptures the starch granules. The loose starch leaks out of the grains and forms a gluey gel, which gives sushi rice its cohesion and risotto its luxurious smoothness.

But you made a lot of rice, and you have some left over. It’ll be great tomorrow, right? You put it in the fridge.

As the rice cools and the hours pass, the amylose molecules that were gelated by the heat start to creep back together, squeezing out some of the water that held them apart, and forming microscopic crystals throughout the grain. The water that was keeping the molecules separate in the gel is bound up inside the amylose crystals.

In the morning, the grains of rice are hard and feel dry. They haven’t actually lost water: It’s just sequestered away in the amylose crystals. The starch has retrograded. (One reason many cooks prefer day-old rice for making fried rice is because, with the moisture locked inside, the surfaces of the grains are nice and dry so they sear rather than steam in the hot wok.)

The same thing happens with all starchy foods. Foods containing less amylose and more amylopectin, like baked potatoes or cold pasta, don’t get as crunchy as our rice, just firmer. Short-grain rice, with its higher ratio of amylopectin to amylose, is still pleasantly chewy the morning after. That’s because when amylopectin retrogrades, which it does more slowly than amylose, it makes softer, less tightly bound crystals.

Retrogradation isn’t just an annoyance; it’s also a useful property of starch, and not just for fried rice. For instance, the injunction to WAIT after you take a fresh-baked, incredible-smelling loaf of bread out of the oven before you cut into it is not just to torment you: The important thing that happens during those agonizing minutes is that the amylose in the bread retrogrades as it cools, turning from a gummy and somewhat formless hot mess into a sliceable, chewable structure.

Over the next few days, of course, the amylopectin in the bread retrogrades, which is part of what makes it turn stale.

Starch in its retrograded form is much less digestible, because the starch crystals can’t be readily broken down by our stomach enzymes, which one researcher has taken advantage of to devise a lower-calorie way of cooking rice. Sudhair James’s method involves cooling cooked rice mixed with oil, which locks away some of the starch in the form of bound-together complexes of retrograded amylose and fat. Those can’t be readily digested, and thus don’t contribute calories to the meal.

Those starch and fat complexes, which lock the starch in its retrograde form, are an exception to a very good rule: Reheating starchy foods, like rice or bread, will reliably cause the starches to re-gelate and become delectably tender once more.

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Graphics by Sophie Greenspan.

When I take a taste, the citrus is there, but it’s more sour than sweet. There’s an overall dullness and a hint of something that reminds me of corn husks. Floral notes are nowhere to be found. It’s not terrible coffee, but it could be much better. The question is how?

I pride myself on making an excellent cup of coffee. I splurge on freshly roasted beans from estimable sources, I’ve fine-tuned my grinding and my water temperatures, and I know how small changes in these variables affect the taste of the brew, which I like black and a little short of piping hot. Now I’m going a step further.

Instead of buying one pound of ultrafragrant beans from my local roaster, I’ve spent only a little more to mail-order five pounds of raw, green coffee beans, and I’m roasting them myself. The descriptors on the bag serve more as a hopeful direction-finder than a guarantee of what’s inside. Home roasting is much more affordable per pound (green beans run $5 to $7, less in large quantities, with minimal loss of quality). But more importantly, it gives you control. Brewing has its ins and outs, but the real power is in the hands of the roaster. It’s in the act of roasting that the flavors in the cup are shaped, and the promise of the green bean is fulfilled. I want that.

ROASTING AT HOME: THE BASICS

Until it’s roasted, green coffee has little of the appealing character of the stuff we drink. Certainly there’s no chocolate or fruit to be discerned in the bag I’m working with. I stick my nose over the bag and inhale. There’s a haunting piney, winy smell. It’s nothing like brewed coffee.

By carefully planning how much heat the bean gets during the various phases of roasting, an experienced coffee roaster can manipulate how the final cup will taste, accentuating particular characteristics, muting others, and even developing the mouthfeel and body of the beverage. A novice, on the other hand, can turn a fine green coffee into an acrid, charred mess; a pale and sour brew; or, with practice, a drinkable but unexciting cup. To roast beans to just the right degree of doneness requires attention to smell, appearance, sound—but this is just the beginning. Getting much beyond that takes finesse. I’ve been working on this project for a while.

I weigh out a fresh 5-ounce dose of green beans—a small juice glass full—and get my roasting machine, the FreshRoast SR700, ready.

The FreshRoast SR700 ($259 on amazon.com) is in essence a fancy version of the hot-air popcorn popper in which I scorched my earliest roasting experiments. The FreshRoast works by blowing air through a glass chamber of beans from below, levitating them mesmerizingly. I drop in my beans, fire up the machine, and set the airflow (high) and the temperature (medium). Over several minutes, the coffee beans darken in color from yellow to tan to browner and browner, start to smell toasty and enticing, and eventually, bean by bean, give off a popping sound. I make a couple of adjustments to the settings as the roasting proceeds, lowering the airflow when the beans get less dense and increasing the heat gently. As the frequency of the pops dwindles, I hit the button that triggers the cooling cycle, ending the roast with cool air blowing through the browned beans.

A screen on top of the machine catches the flaky chaff that blows off, but the main improvement the FreshRoast provides over a popcorn popper is control. A USB connection to my laptop allows the temperature and airflow to be adjusted in increments, and whole sequences of changes can be saved as repeatable programs.

And the biggest lesson I’ve learned thus far? Sequences of changes are key to roasting coffee.

On a basic level, roasting a coffee bean is like roasting a turkey. Like a bird, the bean starts off cool and gets hot; like a bird, heating the bean causes a set of physical and chemical changes.

In coffee roasting, though, there are a lot of things going on that never happen in a turkey. If a turkey’s white meat and dark meat hit the temperatures you want them to, and along the way the skin gets crisp and golden, congratulations: you’ve successfully roasted a turkey. It doesn’t make that much difference what happens between its starting and finishing temperatures.

Two identical batches of coffee beans, however, roasted in the same machine, on the same day, to the same final temperature and color, can smell and taste radically different.

The contrast lies in the journey the coffee beans take from the beginning of the roast to the end. Is there a lot of heat at first that then tapers off? Is it slow, steady heat? Maybe the temperature got a boost toward the end, pushing the roast over the finish line.

That nuanced trajectory, which skillful roasters shape with a carefully planned series of adjustments throughout the process, is called the roast profile.

Countless chemical reactions happen during coffee roasting, and they happen at different moments, at different rates, and to different extents, depending on the specific evolution of the temperature of the bean over the roasting time. As a result, different flavors are created (or destroyed), and those differences are evident in the cup of coffee we drink.

In my next roast of the same beans, I go a little longer and make them a little darker. Now I definitely taste the promised chocolatiness, and the body is heartier, but it still tastes flat and like cardboard to me. By roasting longer, I’ve made it richer but lost some of the earlier acidic brightness that comes with a lighter roast. Worst of all, the cup of coffee has very little aroma at all. It lies flat in the cup. Maybe I should tuck the FreshRoast discreetly back in its cabinet and leave roasting to the pros.

COFFEE BEAN SCIENCE

When you roast green coffee beans, their color, not surprisingly, begins to change.

The bean, which starts off anywhere from steel gray to pea green, fades first, as its green chlorophyll breaks down. Then, as the Maillard reaction kicks in, the bean starts to turn yellow, then tan, then deeper and deeper brown.

The Maillard reaction, which develops flavor as well as color, is responsible for the delicious hue of very many of our favorite brown foods, from grilled steak to crusty bread to dark, malty beer. Amino acids and sugars in the coffee interact in a complicated cascade of reactions, producing hundreds of flavor compounds and compounds called melanoidins, which give coffee its brown color.

As the beans continue to get hotter, caramelization happens as well. While the Maillard reaction happens between sugars and amino acids, caramelization involves sugar alone. The main sugar present in green coffee is sucrose, which doesn’t partake in the Maillard reaction. Instead, the sucrose caramelizes, breaking down and yielding additional brown compounds.

If roasting continues further, the brown color will edge toward black, as sugars and cellulose begin to break down into carbon.

Color is not all that changes. As coffee roasts, it loses mass. The darker a coffee is roasted, the more it loses: water exits the bean in the form of vapor, and so do carbon dioxide, free nitrogen, and volatile compounds. A batch will typically lose 10 to 20 percent of its starting mass during roasting. At the same time, each bean can double in volume, due to the puffing when the vapor escapes.

LEARNING FROM THE EXPERTS

After the most recent dispiriting cup, the one that smelled like plain hot water, I figured it’s time to get some expert perspective.

Sweetleaf in New York, where I drink a lot of excellent coffee, has a sure yet delicate touch with roasting, so I invited myself to watch Rich Nieto, the owner, preparing to make espresso. He dumps 20 kilograms of green coffee beans into the heated belly of his Joper roaster, a Smart car–size machine from Portugal with a napped black metal finish that makes it look like a goth Thomas the Tank Engine.

Where my home machine uses a flow of hot air, the Joper, like most commercial roasting machines, is built around a rotating drum, sort of like a clothes dryer, that tumbles the beans above a powerful gas burner. While it does, our eyes stay on the screen of the laptop hooked to the Joper, where a temperature graph is slowly etched from left to right. The beans’ temperature rockets upward, 200°F (93°C), 250°F (121°C), slowing gracefully as it passes 300°F (149°C). Nieto dances back and forth between the screen and the roaster, making small, choreographed adjustments to the temperature and airflow to help the coffee beans follow a precise path along the graph.

Most modern roasters use software that translates the thermometer readings from within the machine into real-time curves that clearly illustrate the course of a roast. The typical curve, plotting temperature on the vertical axis and time from left to right, looks like a gracefully ascending checkmark: ✓. First, the temperature inside the roaster drops sharply: that’s when the beans went in. Then it climbs in a rise that slowly and smoothly rounds out, until the beans hit their target temperature and the roasting is over.

The screen also tracks other data; Nieto in particular keeps a very close eye on a line that calculates the rate at which the temperature is rising. The heat should keep increasing throughout the roast—I make a mental note for my home roasting—but, he emphasizes, the rate of the rise should go steadily down. I start to wonder if I should stick to turkey roasting.

These beans, destined for the blend of coffees that Sweetleaf uses for its espresso, are Colombian, and Nieto is roasting a dozen batches of them today. “Colombians take a lot of heat nicely,” says Nieto. “But with too much heat up front, it’ll taste tight, like a wine that needs to breathe. Too long a roast, it tastes flat.”

Right around 386°F (197°C), the steady purr of tumbling beans gives way to a sound like popping corn. Much like popcorn does, the coffee beans are fracturing and puffing as steam forces its way out of them. The tiny glass porthole in the Joper shows that they’ve roasted from pale green, through tan, to what now looks like a highly drinkable light brown. But Nieto has eyes primarily for the curves on the screen. A few minutes later, the beans are still making occasional popping sounds when he opens a hatch in the front of the drum and they flood fragrantly out into an air-cooled tray.

Those popping sounds are important. Coffee provides a pair of audible milestones during roasting, when the beans release energy, called first crack and second crack in the trade. As I experienced at Sweetleaf, first crack typically happens around 385° or 390°F (196°C or 199°C), and sounds very much like corn quietly popping. It occurs when the tough, woody cellulose of the bean can no longer withstand the increasing pressure of the hot water vapor inside, and it bursts out. The bean doesn’t explode like popcorn, but it puffs from within, becoming less dense, more porous, and more brittle. If those physical changes didn’t happen, grinding coffee and extracting flavor from it would barely be possible, given the gravel-like density of unpuffed beans.

At Sweetleaf, the roast is stopped not too long after first crack, around 405°F (207°C); Nina Glikshtern at Ninth Street Espresso in Manhattan continues just a little longer, until 418°F (214°C). At home, I’m mostly following suit. But those roasters who continue longer (to around 440°F), in pursuit of a darker roast, are rewarded with second crack, which is “like bacon sizzling in a pan,” says Gabe Cicale of Monkey Joe in Kingston, New York. Cicale’s description is corroborated by the light, rapid crackle of deep-brown, gently smoking beans falling into the cooling tray of his Diedrich roasting machine.

Second crack is when the cellulose itself starts to weaken and break apart under the influence of sustained heat. Carbon dioxide pushes out from the fractured cell walls, and so do oils, which will glisten and bead on the surface of darker-roasted coffee beans.

Even with an extended stay in a 500°F (260°C) oven, a turkey won’t rise above 212°F (100°C), except on the very surface, because the abundant moisture inside it keeps the temperature low. That’s a good thing, unless you want turkey jerky. But in a little coffee bean, what little water is inside the bean evaporates and makes its exit, so most of the roasting takes place at temperatures above the boiling point of water, in the 200°Fs to 300°Fs (93°C to 149°C) .

The things that happen at these temperatures—caramelization, the Maillard reaction, Strecker reactions, pyrolysis—are essential to coffee’s flavor.

“Green coffee starts with 500 or 600 flavor chemicals, and roasted coffee probably has 1,000,” Scott Rao tells me. “But in the process you create millions and destroy millions.”

Rao is a jet-setting coffee consultant, author of professionals’ vade mecums, including The Coffee Roaster’s Companion, and friend and mentor to Rich Nieto.

A couple of mornings after roasting, I visit Nieto again, to evaluate the roasts we did. Rao happens to be in town, and we all meet up at Sweetleaf, where roaster Germán is preparing a blind cupping of dozens of different roasts. We bend over a table on which identical cups of hot coffee are laid out in a long line, giving each one deep sniffs, then, as they cool, tasting them with spoons. The differences from cup to cup are subtle—as intended, since Nieto has a particular flavor profile in mind that he’s trying to achieve in every cup. I pick up apricot, a tea-ishness, a faint tartness in the lightest roasts.

Rao works his way down the line of brews in lightning-quick succession. In between loud, aerated slurps, he offers quick notes: “These two are awesome . . . Good juiciness . . . A little more flatness on this one . . . There’s scope to roast this lighter.”

After the cupping, Rao runs me through some of the ups and downs of a properly planned and executed roast trajectory. As he describes a particular bugaboo of his—a defect called baked flavor—it starts to dawn on me that this may be the very thing that’s preventing me from getting the sweet cup I want. When a coffee spends too long in the roaster without enough heat, its sweetness and fragrance ebb away. Rao’s book on roasting discusses this phenomenon in detail: “If the ROR (rate of rise) is constant or horizontal, even for just 1 minute, it will also destroy sweetness and create ‘flat’ flavors reminiscent of paper, cardboard, dry cereal, or straw.” This sounds very much like the dull, corn husk–flavored beverage I’ve been contending with. Kenneth Davids, in his helpful book Home Coffee Roasting, calls this maltreated coffee: “The taste in the cup is flat and without aroma.”

As roasting progresses and coffee beans get darker and darker, the nature of the resulting cup evolves. Early in the roast, the flavors that predominate are characteristic of the bean itself: floral flavors highlighted by bright acidity. With longer roasting, that starts to give way to sets of flavors that come from the roasting reactions: caramel, darker fruit flavors with less acidity; then more bitter, spicy, chocolaty flavors, until finally the coffee tastes harsh and burnt.

How all the flavors develop during the roast is, of course, complicated. The Maillard and caramelization reactions produce vast families of flavors, only some of which are the toasty, nutty, malty ones we commonly associate with these reactions. The longer these reactions continue during the roast, the more of their end products that are in the cup.

Acidity in coffee comes partially from acids generated by the Maillard reaction, mostly acetic acid (the acid in vinegar). These increase, then decrease, as roasting continues. Other acids are naturally present in the bean: these include citric (the acid in lemons), malic (the acid in apples), lactic (the acid in yogurt), and most predominantly, a family called chlorogenic acids. During roasting, all these acids convert into many more different acids, a complex balance of which gives the final cup a lot of its character. Of all the compounds in coffee, writes Joseph Rivera, who was director of science and technology at the Specialty Coffee Association of America, “by far the most important when dealing with cup profile are the organic acids.”

Although caffeine is bitter, it’s not the main ingredient that gives bitterness to coffee. An alkaloid called trigonelline makes lighter roasts bitter, but it degrades during longer roasting; meanwhile, chlorogenic acids break apart into a number of bitter by-products that create the majority of the bitterness in dark roasts.

The sugars that abound in ripe coffee beans break down during the roast, but other sugars are formed, making a cup of coffee with real sweetness an elusive, sought-after goal. Cooling the beans after the roast as rapidly as possible is a major factor that helps convey sweetness to the final beverage.

Sugars, dissolved minerals, bitter and astringent compounds, and most acids contribute primarily to the taste of coffee but not to its aroma. Aroma is the province of 1,000 or more volatile compounds that emerge during roasting, the development of which is the most elaborate and least fully understood aspect of the process. A modern coffee shop menu is laden with aroma descriptors: peach, jasmine, tobacco, walnut, tangerine. All these impressions proceed from the aroma compounds. “There are several times more going on in coffee than there is in a glass of wine,” Rao says.

BRINGING IT ALL HOME

I’m determined to make it happen at home. I return to the FreshRoast, armed with the hypothesis about long baking and also with some new technology. I’ve wired in a pair of thermocouples to monitor the second-by-second temperature of the air inside the roaster and in the heart of what’s technically called the “bean pile.” On my laptop, I’m running Artisan software, an open-source equivalent of what Nieto uses to watch his temperature curves and his rate of rise.

Being able to see the curves helps—a lot. Now, for each batch I taste, I can review what happened during roasting and spot what might have gone wrong—or right.

To prevent baking, as I learned, the line that shows the rate of rise of the beans’ temperature should descend steadily: That is, I want the heat to keep increasing all the way through the roast, but increase more and more slowly. To achieve that means giving the beans a bigger wallop of heat right at the beginning—I start preheating the machine before dropping the beans in, instead of putting them into a cold machine—and I very carefully ease the heat down as the roast progresses. I go through a dozen roasts in this manner.

Keeping the rate of rise steady is not as simple as Nieto makes it look. In particular, the line has a definite proclivity to tick up as first crack ensues. That makes sense, since at that point, many of the chemical reactions happening inside the bean are exothermic—releasing heat—so in effect the beans are roasting themselves. To compensate, I have to predict when that’s about to happen and turn down the heat a little bit beforehand. On the occasions when I get it right, I can taste the sweetness.

Friends who try my coffee agree it’s getting better. I’m learning to spot when the tartness fades, when the fragrance develops, how to build more fruity character, when it shades into too much bitterness. I have yet to produce a gloriously sweet and juicy cup, but the elements are falling into place. Maybe the next roast will be the one.

PAUL’S TIPS FOR PERFECTING YOUR HOME CUP

The crucial principle when trying to perfect a process like making coffee is to carefully track what you do each time, so you can reproduce it exactly and keep elements from fluctuating unnecessarily while you deliberately change one variable at a time. If you just eyeball how much ground coffee goes into each brew, your road to perfection is going to be a lot steeper.

To that end, invest in equipment that lets you measure as many factors as possible. For brewing coffee, that includes:

A digital scale. Weigh out your ground coffee exactly. You can weigh your water too—if you get used to it, that can be more convenient than a measuring cup. A milliliter of cold water weighs exactly a gram. Some scales, like the Acaia, are designed specifically for coffee brewing. (EDITOR’S NOTE: If you want a general purpose digital scale, the test kitchen recommends OXO.)

A digital thermometer. A couple of degrees of difference in the water that you use for brewing can make dramatic changes to the final brew. Lower temperatures tend to accentuate sour tastes in coffee, and higher temperatures accentuate bitter tastes. The sweet spot is typically around 194-204°F. Some electric kettles, by Pino or Bonavita, will hold water at a temperature of your choice. (EDITOR’S NOTE: The test kitchen recommends this one, from Zojirushi.)

A digital timer. Manual brewing methods benefit from as much precision as you can give at every stage of the process. (EDITOR’S NOTE: America’s Test Kitchen’s winning kitchen timer is an OXO.)

As you start to become even more of an obsessive, I mean connoisseur, you’ll want kits to test the pH and hardness of the water you’re using. And, going even further, there is the coffee refractometer.

This handheld device, a mainstay at serious cafes but not too often seen at home, shines light through a droplet of brewed coffee and measures the angle of refraction as it passes through. Using this info, you can calculate the exact strength of a brew, measured in the Total Dissolved Solids present in the liquid. Being able to precisely measure the strength of each cup is the ultimate tool for fine-tuning, and then getting right every time, your coffee. The coffee refractometer made by VST is designed to be used with that company’s software, which can analyze, calculate, and scale up or down coffee formulas for any purpose.

If your brewing is all you want it to be, and you want to plunge back into the unknown and drink a lot of bad coffee while you patiently strive for a new level of excellence, you might enjoy roasting.

The FreshRoast SR700 is good for us diligent measurers because of its ability to hook to a laptop. At another price tier, so are the Hottop models. But even a $50 stovetop pot with a hand-cranked agitator—designed for popcorn but ideal for coffee, especially since it can hold much more than the FreshRoast—can become a scientific cook’s tool, with a little added technology.

Having a thermocouple thermometer that connects to a computer is a handy device for many kitchen tasks—it lets you watch and log temperatures on your computer. There’s a wide variety on the market: some have a single probe, some accommodate an octopus of probes to monitor the temperatures of many things at once. Some connect via USB, some are wireless.

A page on the Artisan software site lists a number that are explicitly compatible, although that’s not an exhaustive list.

Insert a thermocouple probe so its tip rests among the beans in the roaster, be that the Whirley-Pop or the FreshRoast. A second probe monitoring the air temperature is optional but helpful.

Install Artisan and set it to work with your thermocouple, and you can watch and record every moment of every roast you do, notating when first crack happened, what the beans weighed going in and coming out, and of course watching the rate of rise.

Most important, taste everything, a day or two after roasting, and correlate the variables that changed in each batch with how it tastes. You can use the official cupping protocol of the Specialty Coffee Association of America or an approach better suited to your home and habits, but the road to amazing coffee is the same: measure, record, notate, taste, practice, repeat.

Photography by Kevin White.

Pop quiz: What do all these items have in common? The crackly crust on fresh-baked bread. Lollipops and other hard candies. The crisp skin of roast chicken. Crunchy, puffy Cheez Doodles. Crackly breakfast cereal. Your kitchen window.

If you said “they’re all delicious,” you just might be this kitten I used to know who loved licking windowpanes. Partial credit for that! But the answer we’re looking for is: On a molecular level, those are all forms of glass. That’s why they crunch and shatter.

A glass, by definition, is a solid substance whose molecules are amorphous, all pushed together indiscriminately. In that way, it has more in common with a liquid, full of disordered swirling molecules, than with a crystalline solid such as salt, in which all the molecules are neatly ordered, each facing the same direction and tucked closely together like bricks in a wall.

The world—including the edible world—has many different glasses. Silicate glass, the stuff we drink wine from, wear to correct our eyesight, and hurl bad guys through in action movies, is just one of them.

Where do glasses come from? A soft substance, or a viscous liquid, will form into a glass under particular circumstances; typically if it’s heated—which removes moisture and mobilizes the molecules into an amorphous state—then cooled rapidly.

Hard candies are made by heating a sugar syrup above 300 degrees F/148 degrees C, to remove all of the water; then quickly cooling it till it solidifies, molded into whatever shape you please. The key is for it to cool quickly. If the sucrose molecules have time to carefully arrange themselves into crystals by the time the candy solidifies, you’ve got a crumbly candy filled with crystalline grains (think rock candy). But if they’re still disorganized when it becomes solid, you get a perfect glossy glass. For this reason, also, candymakers often use a variety of different types of sugar—sucrose, fructose, glucose—in a single recipe. In a candy made of all identical sugar molecules, the molecules nestle sweetly together into gritty crystals very readily, but if the molecules have slightly different shapes, they don’t crystallize as easily.

Other edible glasses are made in the same basic way, as far as physics is concerned. Raw chicken skin has a texture that science calls “rubbery.” As it’s heated, it loses water, and the proteins in it unravel and form a gel. Once out of the oven or fryer, the molecules quickly cool and set into, yes, a glass.

The same gel-setting process happens with other things we like to crunch, like starchy snack foods and crusty bread. The water in a bread dough keeps it soft and pliable, but as it’s heated, some of the water evaporates from the outside of a loaf. At the same time, the starch molecules loosen their holds on each other, a process called gelation. These jumbled molecules are ready to change to a crackly, glassy crust as they cool.

The amorphous nature of glassy materials, with random gaps between the molecules, means that they’re inherently not as stable as other states. Over time, especially in the presence of warmth and humidity, a glass tends to either grow internal crystals—which is why those butterscotch candies that have been in your purse for months are sticky and crumbly—or absorb water and lose its rigidity, which is why the crust of last week’s rustic loaf has a leathery chew.

The next time you crunch into a hot, crisp French fry, snap a ginger snap, or whack peanut brittle till it shatters into manageable pieces, take a moment to appreciate its special, delectable texture. Raise a glass!

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Graphics by Jay Layman

When it comes to Hollywood, in an era of digital special effects and computer-generated monsters, one of the last provinces of traditional analog elements is Foley art: the sounds that are added to movie scenes to give extra vividness to a head thwack, a creaking chair, or just the ever-present sounds of walking. These sounds are still created using physical props—and very often, those props come from the kitchen.

Jeremy Bloom is a New York sound designer who works in theater and radio as well as film. “Recording the actual sound of a thing,” he says, “is often not as effective as recording something else entirely.” So out comes the food. Coffee grounds on the floor can sound like dirt when recording footsteps. Footsteps crunching in snow might be created with a dry cornstarch mixture. And, he says, “for any violence, it’s all vegetables and fruits.”

Tim Prebble, a sound effects editor and designer from New Zealand, describes how he would artfully create the sound of a punch in the face. “The initial impact of the punch might be from slapping or punching a melon, combined with a tightly synced cabbage hit. If the punch landed near the mouth, we might then use some crushed shellfish combined with a pumpkin, melon, or seaweed break to emulate a jaw crack. Depending on how extreme the hit was, we might then transition into cartilage and gore sounds, as the jaw and head compressed, using egg and green pepper breaks. Once the main violence was over, add some more subtle orange squelches and shellfish moves.”

After using techniques like those in a few films, Prebble decided to record and make available a high-quality library of thousands of such sounds, titled Vegetable Violence. He unleashed an arsenal of machetes, hammers, saws, fists, and other weapons to wreak havoc on a hapless array of vegetables and fruits. The downloadable library includes almost 100 samples of pumpkins being stabbed; 52 cabbage heads beaten with bats; 110 “melon squelches”; and quite a bit more.

“A lot of time was spent on pumpkin cracks and gouges, and various melons. We also discovered by applying pressure to the inside ‘guts’ of a melon, we could create a vacuum, which created great sounds! Another discovery was if you crushed shellfish wrapped in a tea towel, it sounded like very nasty jaw and teeth movement.

“After each recording session, there was always a slight odor left, like a very strange salad.”

What’s in the Foley Artist’s Pantry?

CABBAGE AND LETTUCE

Hitting a head of lettuce or cabbage in close proximity to a microphone is “the most classic way” to emulate a punch sound, says Bloom.

CELERY

Perfect for cracking and crunching of bones. Wrap it in cloth first for a more muffled crack.

CHICKEN

To create the sounds of breaking bones, “I personally like putting things in (cooked) whole chickens and then beating the chicken with a sledgehammer or other bludgeoning device.” – Billiam Baker via http://www.epicsound.com/sfx/

COCONUT SHELLS

Can be clacked together for hoofbeats, as seen in Monty Python and the Holy Grail.

CANNED DOG FOOD

“The chunky stuff isn’t so good, but the tightly packed all-one-mass kind makes gushy sucking sounds when the air on the outside of the can is sucked into the can to replace the exiting glob of dog food. This sound can be used as an element in certain kinds of monster vocalizations, alien pod embryo expulsions, etc.” – Ashley Walker via http://www.epicsound.com/sfx/

MACARONI AND CHEESE

“Having just eaten a bowl of macaroni and cheese shells, I have to say it’s the most convincing tentacle sound I’ve ever heard. Use the rounded shells specifically as they have little pockets for air and extra squishy sounds. You get that suction cup action going, literally.” – Jay Semerad via http://www.epicsound.com/sfx/

SODA

“Pouring a fizzy drink onto tarmac or any floor is supposed to be very good for sea, or that’s what they used in Jaws anyway.” – Matt Sugden via http://www.epicsound.com/sfx/

VEGETABLES

“For the sound of growing plant tentacles or roots crawling up walls and grasping objects, try squeezing some raw vegetables—like iceberg [lettuce], green peppers, or asparagus. Also perhaps stirring in some pasta sauce and add some whooshes if they grow fast.” – David Filskov via http://www.epicsound.com/sfx/

WATERMELON

“Any stab you hear, that’s usually a watermelon,” says Bloom.

Photography by Kevin White.

Oil and water don’t mix. It’s a truism we learn in elementary school. “Like girls and boys in the lunchroom,” the teacher said.

Why don’t they mix? They’re different kinds of molecules. Each molecule of water has two ends, one with a positive charge and one with a negative charge, and, just like in magnets, the opposite poles attract each other. Water molecules cling together, with the positive pole of one water molecule sticking to the negative pole of the next. Water also clings to other kinds of molecules that have charged poles, like salt or alcohol, forming a solution.

But oil molecules have no positive or negative charge—they are non-polar—and so water is indifferent to them. The two kinds of molecules have no way to cling together, so they stay in their separate areas, like middle schoolers at a dance.

If you have a blender, or a good whisking arm, you can get them to play nice for a while. Forcibly whipping oil and water together will break the oil up into little droplets, which aren’t individually buoyant enough to push through the water and form a separate layer again. Or at least, it takes them a little longer to do so: long enough to pour a shaken vinaigrette onto a salad, but not long enough to store it in the fridge without needing to shake it up again next time.

This is an emulsion: a mixture in which small drops of one substance are dispersed throughout another substance. But how can we keep it from coming apart after a few minutes? An emulsifier.

Emulsifiers are like kids who are friendly with the girls’ clique and the boys’ clique. A common example is lecithin, which is found in egg yolks, soybeans, and other sources. It’s a large molecule with one part that’s attracted to oil, and another part that’s attracted to water. So when it’s mixed in with oil and water, a lecithin molecule grabs on to an oil droplet with its fat-loving end, and with its water-loving part facing the water. With the emulsifier encouraging them to intermingle, an emulsion can stay stable for a much longer time. It’s still made out of oil droplets dispersed in water, but the emulsifying molecules attached to each oil droplet let the droplets stay cozily mingled with the water instead of rising to the top.

That’s why there’s egg yolk in mayonnaise—the lecithin in the yolk emulsifies the oil and the vinegar together. (For emulsion purposes, vinegar is basically water.)  Milk is an emulsion too, with droplets of butterfat dispersed throughout a watery medium. So are cheese, ice cream, tahini sauce. Even hot dogs: during manufacturing, the finely ground meat smoothly emulsifies fat into water inside the dog.

When oil and water are emulsified together, the emulsion has different properties than either of its components. Mayonnaise is thicker and creamier than either oil or water because, in order for it to flow, the water and the oil droplets have to slow down and move around each other, instead of pouring smoothly like either ingredient can when it’s on its own.

Its emulsion nature is also why mayonnaise is opaquer than oil or water: Even though the oil droplets are tiny (about 10 micrometers in diameter), there are millions of them, and light bounces off their surfaces, rather than passing through as it does in pure oil or water. Some industrially produced nanoemulsions have much smaller droplets—just a few billionths of a meter in diameter—which is too small to reflect light, so the emulsion appears transparent. Many citrus sodas, for instance, contain nano-emulsified essential oils.

Mayonnaise is an example of an oil-in-water emulsion: oil droplets are dispersed in water, which is the “continuous phase.” Oil-in-water is the most common kind of emulsion in the kitchen—milk, ice cream, cheese, the finely ground meat in hot dogs, and tahini sauce are all examples—but it’s not the only kind. Butter is a water-in-oil emulsion: its fat content is so high that it forms the continuous phase, and droplets of water are dispersed through it. So is peanut butter.

So you see, kids, many of the most delicious foods can only happen when different types of substances work together. What do you think about that?

Is there a word you wonder about? Email us!

Graphics by Sophie Greenspan

You can put food through this training too. All you need is a centrifuge.

Like astronauts, food and drinks are also highly susceptible to gravitational forces. Shake a bottle of cloudy apple juice, then leave it on the counter for a few hours. Under the force of gravity, the denser solid particles of fruit matter will slowly sink to the bottom.

The sedimentation that occurs naturally under normal Earth gravity happens much faster and more dramatically in a centrifuge, a machine designed for laboratories but now more and more popular in bars and restaurants. A tabletop centrifuge can spin at thousands of RPM and produce a force that’s thousands of times stronger than Earth’s gravity. As a juice or other mixture whirls in the ’fuge, it will separate into layers, with the denser components moving to the outside of the container.

Bars use centrifuges for exactly that purpose. The result? Clarified juices. (The main reason to clarify juice is that cloudy juice can’t be carbonated without frothing up, since the denser particles attract carbon dioxide bubbles. Clearing them out in a centrifuge means that any juice can be easily carbonated, making it easier to create new and interesting cocktails.)

Many other effects are possible by centrifuging food ingredients: concentrating syrups, turning normal yogurt into Greek-style thick yogurt, clarifying butter. Some of the earliest centrifuges were created to separate cream from milk (fat is less dense than water, so cream rises).

The Modernist Cuisine cookbook offers a number of recipes for centrifuge owners to try, including extracting hazelnut oil from roasted hazelnuts and separating out the natural fat that’s in green peas.

That was the first centrifuge recipe I tried at home, when the Modernist book came out in 2011. I had inherited a small centrifuge that fit on my counter, and so I immediately pureed peas, spooned them into six little test tubes, and fired the centrifuge up.

After several minutes of spinning, I stopped the machine and opened the test tubes. On top was a layer of clear green pea juice; on the bottom was starchy pale-green pea solids; and in a very thin layer between the two was pea fat. Success! The only hitch was that, from almost a half cup of peas, I was able to scrape out only about a half teaspoon of pea butter. The kind of centrifuge I could realistically fit into my apartment kitchen (like this one) was just too small to produce a useful amount. And the centrifuges bars use take up more space than my whole oven, cost thousands of dollars, and are very finicky to use.

That’s why I was excited to learn about the Spinzall last month, a new culinary centrifuge invented by my friend Dave Arnold and currently available for preorder. Although it’s no bigger than a food processor, it explicitly addresses that problem of small yield—instead of placing the ingredients in a spinning rack of test tubes, the Spinzall has just one big bucket, which can hold a half liter. There’s also a way to continuously pump food into and out of it, so you can get as much yield as you want.

I spoke to food writer and scientist Harold McGee about the possibilities that the Spinzall opens up for the home cook.

“The first thing that comes to my mind here in my own kitchen is being able to clarify stocks quickly rather than waiting for the separation of fat and liquid at 1G. I don’t currently do a lot with seed butters and oils or fruit juices, but that could change with a tool that looks so easy to work with. I’d love to make an oil from the amazing mango-flavored pistachios that I can occasionally get from Turkey, and pumpkin seed oil has always intrigued me, with its shifty chlorophyll-carotenoid color.”

We’re not quite at the point where centrifuges are common in home kitchens, but we may be on our way. Pea fat for all!

Do you use a centrifuge at home? Let us know in the comments or on our social media feeds.

When a food changes color in the kitchen, odds are very good it’s becoming brown. There are two main ways that happens: browning caused by cooking, and browning originating with enzymes present in the food itself. Same color, very different phenomena.

If a recipe says to bake until golden brown, we’re dealing with non-enzymatic browning. This is the delicious type of browning. It happens in a few different ways.

The simplest is caramelization. Well, on a chemical level, caramelization is actually quite complicated, but for the cook it’s simple: heat sugar and it turns brown. When a sugar is heated, its molecules break down and react with each other, creating new compounds, some of which are brown and others of which have delightful new toasty, nutty, buttery flavors.

When you caramelize onions, carrots, or the like, it’s the sugar in the vegetable that’s changing, so the sweeter your vegetable is to start with, the sooner and more thoroughly it will caramelize. Raising the pH with a pinch of baking soda will speed up the process. (Be careful: too much baking soda will make carrots mushy by weakening their cell walls.) 

If proteins are present, things get a little more elaborate. When you grill a fish, the sugars present in the fish undergo caramelization, but at the same time, other reactions take place: the renowned Maillard reactions. Maillardization is a totally different kind of browning, which requires two partners: sugar and the amino acids that make up protein. The two come together and set off a dizzying set of reactions and interactions, resulting in, again, both brown molecules and many, many different delicious flavor molecules.

The specifics of what happens during Maillardization, and what flavors are produced, depends on numerous factors, including what other molecules are present. One of the reasons cooked beef tastes the way it does is because the iron in its blood leads the Maillard reactions down certain pathways; the Maillard reactions that happen in fish, in pancakes, in roasting coffee beans, are all very different and result in each of those foods’ differently delectable cooked flavors.

Caramelization and Maillardization can—and usually do—both happen together. In a typical cooking scenario, Maillardization starts first, and then caramelization kicks in at a slightly higher temperature, with each set of reactions contributing its own inimitable character to the food.

They can even happen very slowly and at low temperatures, as in black garlic, which is made by cooking regular garlic at around 140 degrees F/60 degrees C for a month or longer, giving it a unique, savory flavor; or in wine as it develops nutty, toasty notes over years aging at cool temperatures.

Despite appearances, the deep brown-to-blackening when food chars isn’t just a further degree of Maillardization or caramelization, it’s a different set of reactions entirely: pyrolysis and carbonization. At this point, sugars and proteins are rapidly broken down into bitter-tasting carbon compounds. A little char can be a nice accent to a food, but no more than a little.

Now, cut an apple or an avocado in half and walk away for a few minutes. When you return, the cut surfaces have developed a brownish tinge. Quite possibly, somebody snuck in and caramelized them while you were gone, but more than likely it was enzymatic browning instead.

Enzymes are proteins with a particular knack for helping other molecules undergo chemical reactions. We are full of enzymes, and so are plants; they’re essential for biological processes, such as photosynthesis or digestion. In the case of our cut apple, polyphenoloxidase enzymes speed up oxidation reactions between oxygen in the air and compounds called polyphenols in the fruit. As a result of these reactions, brown-colored compounds are produced. The same enzymatic processes are responsible for cut potatoes and beets going black; crushed mint and basil leaves slowly developing a swampy taste; bruised bananas browning and softening; and mushrooms discoloring at the slightest touch. The reactions may be an attempt by the plant to protect its wounded tissue, but the biological story is not yet well understood.

Enzymatic browning is an eternal enemy of cooks and food manufacturers, and a number of techniques have been developed to combat it. The tried-and-true method of treating the cut surfaces with lemon juice works because the lemon’s citric and ascorbic acids are both antioxidants: they limit the oxidation of other molecules.

Preventing oxygen from getting to the injured vegetable (as oxygen is needed for the enzymatic reactions to occur) can also work; for instance by wrapping it in plastic or submerging it in a water bath. Destroying (denaturing) the enzyme with high temperatures, exposure to alcohol, or other means will prevent browning as well; that’s why it’s a good idea to blanch cut fruits and vegetables before freezing them. (The freezing itself slows down the reaction but doesn’t prevent it.) And it’s possible to genetically modify crops so they don’t have as much polyphenoloxidase in the first place: That’s the secret to Arctic Apples, which stay white when they’re cut.

Like any enemy, though, enzymatic browning isn’t all bad: It’s also responsible for the browning and accompanying delicious flavor development that takes place after harvest in tea leaves, vanilla beans, raisins, and other tasty brown foods.

“I trust in nature for the stable laws of beauty and utility.” 
— Robert Browning

Is there a word you wonder about? Email us!

Graphics by Jay Layman

That’s how butter was made for centuries, and that’s how Vermont farmer Diane St. Clair makes Animal Farm butter, which aficionados buy for $50 a pound. I visited St. Clair on a cold day in December to learn about how she makes butter, why her product tastes so good, and whether I could come close to her results at home.

Twice a day, St. Clair milks her herd of nine Jersey cows. As the fresh milk sits and cools over a span of hours, a layer of cream rises to the top. She skims the cream off, lets it rest, runs it through a pasteurizer at 150°F (65°C), then adds a little of her own buttermilk and lets it sit another day. The low-fat milk left behind gets fed to the calves.

Live bacteria from the buttermilk start to work in the cream, fermenting some of the lactose sugar into lactic acid, which gives it a distinctive tanginess and also thickens it slightly. After a day, the cultured cream is ready to go into the churn. The Animal Farm churn is a rotating drum, sort of like a clothes dryer, that lifts the cream and lets it drop, over and over, until it becomes butter. Churning a batch of cream can take an hour, but it all depends on the cream.

“In the winter, when they’re eating hay, churning takes longer. In the summer, especially as the grass gets lusher, the butter is fragile and it’s easy to overchurn. Overchurned butter is greasy.”

When the churning is done, St. Clair brings the mound of butter over to a work surface, where she washes off some of the remaining milk solids and kneads it by hand, squeezing out as much moisture as she can. When she deems the texture right, the butter is ready to wrap and sell.

HOW BUTTER HAPPENS

Milk is an oil-in-water emulsion. It’s almost 90 percent water, with dissolved sugars and proteins, and globules of milk fat, each just a few microns across, dispersed throughout. A complex membrane with emulsifying properties encloses each globule. The membrane acts as an interface between the fat and the water, keeping the fat particles separate and suspended. Although the fat particles gradually rise to the top as cream unless the milk is homogenized, the membrane helps them stay at least somewhat suspended in the emulsion instead of becoming an oil slick.

Straight out of the cow, the average milk contains 4 percent fat, though this number varies significantly with what the cow’s been eating and the breed. The Jersey herd that St. Clair has deliberately bred for high fat production can achieve a luxurious 8 percent.

Fat floats on water because it’s less dense, and despite the membranes, over time some of the fat suspended in a container of fresh milk will rise to the top. As a result, after a day or so of sitting undisturbed, the topmost layer of the milk will consist of 35 percent or more fat. This rich top layer is the cream, which is traditionally skimmed off and used by the butter maker.

Cream, like milk, is an oil-in-water emulsion, but a much richer one—the fat particles swimming in the water phase make up 35 to 40 percent of the weight of the cream, rather than just 4 percent in milk. Churning cream into butter basically involves beating air into the cream and slamming the fat particles against each other again and again. On a microscopic level, tiny air bubbles worked into the cream act like magnets for fat. Each air bubble will stick to several fat particles and disrupt their protective membranes, causing the fat to cling to the surface of the bubble. When two air bubbles collide, the fatty layers that surround them merge, creating a larger clump of solid fat. And clump sticks to clump, snowballing until almost all the fat is stuck together in a big mass, and the liquid—the buttermilk—is fat-free.

The mass of fat still contains plenty of liquid, so the final step, after draining it, is to “work” the butter. Traditionalists like St. Clair slowly knead it by hand. At Ronnybrook, a dairy farm in upstate New York, the two women who make butter daily keep spinning the churn for a time after the buttermilk is drained off. Both of these methods have the same effect: squeezing moisture out of the mass of butterfat.

This extra working of the butter accomplishes the ultimate goal of butter making: inverting the emulsion.

What does that mean? As the fat particles coalesce during the kneading phase and moisture is forced out of the spaces between them, the nature of the substance transforms. It changes from an oil-in-water emulsion, where water is the dominant element and fat is dispersed throughout it, to a water-in-oil emulsion. The united butterfat forms a continuous mass, and microscopic pockets of moisture—around 15 percent of butter is water—are scattered throughout it. The network of solid crystalline fat gives butter its firm structure, holding the water in place. As soon as a piece of butter melts, the moisture escapes from its delicate dispersion among the pockets. If it solidifies again after melting, it’s no longer an emulsion. It’s no longer butter, just butterfat.

WHAT MAKES GREAT BUTTER?

Almost all the butter Animal Farm makes is bought by Thomas Keller to serve in his top-flight restaurants, the French Laundry and Per Se. Each year, a small amount is sold to the public via New York’s Saxelby Cheesemongers, where it’s snapped up fast—even at premium price. And understandably: Each little knob of the stuff is radiantly yellow and delicately fragrant. Spread on bread, it’s cool, rich, and unusually complex in flavor, with a lingering nutty nuance.

The butter from New York’s Ronnybrook Farm, which doesn’t go through the culturing step, is delicious in a different way—paler and firmer, with a clean, milky taste that remains on the palate for minutes on end. What makes these butters so different from each other, and so much better than the sticks you get in the supermarket?

Cream

“Especially for sweet cream butter [that is, butter that’s not cultured], you want the cream to be as fresh as possible,” says food scholar and author Harold McGee. As cream spends time outside the cow, it undergoes a number of changes. Tiny air bubbles that get into the milk during processing and transportation, as well as changes in temperature, disrupt some of the fat. globules and make them clump. Enzymes, both those naturally present in milk and those created by bacteria that grow at low temperatures, start to break down some of the milk fat, which can cause subtle off-flavors, as can the presence of oxygen.

And these changes are magnified when cream is concentrated into butter.

Much of the lush nuance of farmstead butter is due not just to the cows’ excellent diets of grasses and flowers, but to the seasonal variability of those diets. “In late summer, with lusher grass and more flowers, there’s more intense flavor, and the texture is much more spreadable,” says St. Clair. The hay the Animal Farm cows eat in the winter is no less carefully assembled: “clover, second-cut grasses, trefoil—and terroir. If I fed a herd the same things in California, the butter would taste completely different.”

When cows are raised on a fixed diet, the cream tastes the same year-round. And a lot of consumers, and therefore producers, prize this consistency. As a result, even many artisanal butter producers buy cream in bulk from creameries that batch together the output of numerous farms and mechanically separate the cream.

Culture

Historically, culturing wasn’t something you did to make your butter better—it was just what happened. If you were a farmer with a cow or two, it’s likely you needed a few days’ worth of cow’s milk to amass enough cream for a batch of butter. As your bucket of cream sat around, waiting in vain for refrigeration to be invented, wild bacteria naturally found their way into it and soured it a bit.

Nowadays, culturing cream is a careful science. Elaine Khosrova, author of the recent book Butter: A Rich History, showed me how she makes butter in her home kitchen, starting with a powdered culture of freeze-dried bacteria made by Danish biotech company Chr. Hansen. The culture contains a precise mix of four different strains of bacteria. Two strains are primarily responsible for creating lactic acid, which gives a tart flavor and lowers the pH of the cream.

As the cream becomes more acidic, the other two strains start to create new aroma compounds; most importantly diacetyl, which is the molecule responsible for what we think of as buttery flavor. Synthesized diacetyl is added commercially to a wide variety of foods—margarine, microwave popcorn, pancake syrup. In the supermarket, it’s increasingly possible to find cultured butters, but commonly, industrially made butter is not cultured. Instead, it has diacetyl added after the fact, to give it the desired aroma. Diacetyl is also produced during fermentation of wine, especially buttery-tasting Chardonnays, and beer, where it’s usually considered undesirable.

Meanwhile, in the now-acidic cream, some of the strands of protein that make up the fat globules’ membranes slowly split off and knit together into microscopic webs throughout the cream, causing the liquid to thicken. The disruption of the membranes also means there’s more free fat floating around and clumping together.

Apart from the magic of witnessing the process firsthand, the main compelling reasons to make butter at home are if you have access to excellent cream or “a really interesting culture,” says McGee. Store-bought buttermilk—which is mostly made by culturing low-fat milk, not as a by-product of butter making—has the right kind of culture for making homemade butter, so it can be a good starting point.

Only a few butter makers culture longer than 48 hours, but long culturing can produce unique, delicious effects, as the bacteria work their flavorful wonders for days. Grant Harrington of England’s & [Ampersand] Butter lets his cream culture for a full week to make it “as buttery as possible.”

Texture

Elaine Khosrova has traveled the world tasting butters, and she gave me tastes of a selection of butters that varied widely not just in taste but also in consistency. “The aspect I’m most interested in these days is texture,” she says. She cut a long, thin slice from a block of French butter and held it up by one end. It was firm yet smoothly bendable, and its yellow surface was shiny and dry. “There’s a lot of moisture in it, but it’s all tucked away in tiny droplets.” We ate the slice. It was delicious.

The texture of butter is mostly a factor of the solid fat crystals that make up its framework. Nestled within the matrix of crystals are bubbles of water, milk solids (mostly protein and sugar), air, and noncrystallized fat.

The majority of the fat in butter is part of that crystalline network, but fat globules that survive churning intact, still snug in their membranes, don’t link up with the crystals. As a result, they don’t contribute to the butter’s firmness, so all else being equal, the more intact globules are in the butter, the softer it is.

Both St. Clair and Rick Osofsky, president of Ronnybrook, emphasize how gently they treat their cream so as to keep the fat globules intact. St. Clair ladles the cream layer off the milk by hand as it slowly rises, and Osofsky keeps all his milk unhomogenized, so even the bottles of Ronnybrook milk for sale in supermarkets have a layer of cream at the top.

The ratio of harder to softer fatty acids in the cream is also a major contributor to texture. Corn-fed cattle give milk with more palmitic acid, a fatty acid that’s solid at room temperature. A diet of grass leads to much more oleic acid, which is unsaturated, and hence liquid at room temperature. When cows are pastured, as St. Clair points out, the summertime milk tends to have a higher proportion of softer fats. The more of the unsaturated fat that’s present in the cream, the softer the butter will be.

The churning method—fast, slow, how much water comes out—and the way the cream was stored prior to churning, also affect texture.

Robert L. Bradley, professor emeritus at the University of Wisconsin-Madison, notes in his technical butter maker’s manual Better Butter that spreadability of butter out of the refrigerator is a surmountable issue. “Considerable research has focused on ideal spreadability . . . The quick fix is to leave butter at room temperature for 2 hours. Mission accomplished!”

MAKING IT ON YOUR OWN

The first homemade butter I ever tasted was a batch my friend made from supermarket cream, without culturing. I was impressed at his enterprising nature and impressed that he could make something just as good as store-bought butter. But, as we realized as the wonder wore off, it wasn’t really any better than store-bought butter. I don’t think he bothered to make it again.

Years later, when I wanted to make butter, I knew that I’d have to go the culturing route. I don’t have a reliable source of particularly good cream in my area and it’s just not practical for me to keep mini apartment cattle—but I do have room for a thriving community of bacteria that can turn ordinary cream into extraordinary butter.

I bought a carton of buttermilk and a few cartons of heavy cream and got to work in my New York apartment kitchen. In playing around with cultures, I tested my homemade yogurt as a starter as well as store-bought buttermilk. Most yogurt cultures don’t include the subspecies of Lactobacillus that specializes in making diacetyl, so creams cultured with yogurt starter instead of buttermilk make intriguing, unexpected butters.

The buttermilk-cultured cream developed a familiar, wonderful flavor that can only be described as buttery, as well as a faint sour tang, both of which got stronger over time. Meanwhile, the culture that started with yogurt developed a sharper, enticing tang but very little buttery flavor—it was a different beast. Out of curiosity, I also tried a batch cultured with a little of each. That one wound up with an interesting rich-and-tart flavor combo, slightly reminiscent of really good cottage cheese. Ultimately I decided on all buttermilk for my recipe.

I also tried using ultra-pasteurized heavy cream, which dominates the shelves at my local markets, instead of regular pasteurized heavy cream, which is slightly harder to find. The ultra-pasteurized product is treated at a higher temperature before it’s packaged, which changes its sugars and proteins somewhat. In my experience, ultra-pasteurized cream takes longer to culture, and the butter it makes has less buttery aroma and a faint but distinct bitter aftertaste.

After 24 hours, the cream sitting out on my counter had thickened and developed a tang. Many butter makers, including St. Clair, stop at this point. Others let it go further, to develop more cultured flavor. I churned and kneaded a batch—remarkably easy!—but it was only slightly tangy and buttery.

Before it’s churned, cream needs to be chilled down below room temperature, to firm up the fat. When I tried churning cream that wasn’t cold enough, it turned into a greasy, mushy mess, with liquid fat mixed into the buttermilk. When I tried saving time by putting cultured cream straight from the fridge into the food processor, it was so thick that it just clung to the sides of the processor bowl, out of reach of the blades. 55°F (12°C) seems to be the sweet spot for churning.

All fats are made up of long chainlike molecules called fatty acids. Milk fat contains a complex mixture of numerous different fatty acids that have different melting points. Because of that mix, butter doesn’t have a single specific temperature at which it melts, like ice does. Instead, it softens gradually as it gets warmer. As we’ve all experienced, butter straight from the fridge is firmish but not rock-solid; as it sits out, it becomes softer but still largely solid.

As cream is held below room temperature, its solid fats lock together in tiny crystal formations. In industrial butter production, carefully manipulating the time and temperatures of cooling affects the nature of these crystals—large, small, uniform, irregular—which influences the final texture of the butter and can compensate for variations in the fatty acid makeup of the cream in different seasons.

After 48 hours of culturing my cream, I made a second batch of butter, and it was more than twice as tasty. It was a full-flavored butter I’d offer to guests. But logically, if longer aging means tastier butter, why stop there?

I let the remaining cream keep culturing, sniffing it every day with a hint of apprehension. It got more and more pungent, but never with that particular “throw it out!” sourness familiar from a neglected refrigerator. After seven days, the aroma was very buttery and also a little cheesy, likely the result of native lipase enzymes in the milk starting to break down some of the milk fat and produce butyric acid, which gives sour milk—and some fine cheeses—their funky odor.

Once this week-old cream was churned, I took a sip of the buttermilk first. It was a lot more acidic than the supermarket stuff I’d started with! But the butter itself was perfect: pliable, tart, rich, and complex, with no off-notes.

Simultaneously, I began working with Dan Souza back at the test kitchen to test a few variables and to get the whole Cook’s Science team to do tastings. We tested a food processor vs. a stand mixer to churn the butter (the food processor won), and figured out the ideal salt content if you want to make a salted version of this butter.

If you want to try your own hand at this deeply flavorful, homemade cultured butter, check out my recipe and go buy yourself some cream.

Photography by Steve Klise.

Food Styling by Elle Simone.

In the course of editing Dan Nosowitz’s story The Very Weird World of Highly Specialized Food Testing Machines, I wound up subscribed to an entertaining email newsletter for users of the Bostwick Consistometer texture measuring device.

Paul, Do You Know the Difference Between Consistency and Viscosity? read one subject line, and I thought, sure I do. Then viscosity was suggested as a Word of the Week (have you sent in your suggestion?) and I did a little reading and found myself in the thick of it.

Viscosity is a characteristic of fluids, and it’s (deceptively) easy to get a handle on intuitively: honey is more viscous than water, and olive oil is somewhere between the two. But—as with many kitchen phenomena—when you look closely, there’s a lot more to it.

The Bostwick Consistometer is a foot-long metal ramp with a ruler along its length and a gated compartment at the top. Fill the compartment with your fluid foodstuff of choice, then open the gate and let it flow down the ramp! The distance it flows in 30 seconds is a measure of its consistency, rather than its viscosity, which is a related but more complicated phenomenon.

That’s a very simple scenario. On the ramp, your nacho cheese sauce or what-have-you is just moving downhill, propelled by the steady force of gravity. The complexities of viscosity come in when different forces are applied: stirring, swirling, scooping.

Back in 1686, Sir Isaac Newton mathematically described the physics of viscosity in his usual elegant way, giving an equation that approximates how a fluid moves when a force is applied to it. The more viscous the fluid, the more it resists moving. However, the real world is not quite that elegant, and every fluid is different. A few, such as water, are called Newtonian fluids because their behavior is actually quite similar to what Newton described. But a lot of the materials we actually deal with from day to day—from toothpaste to whipped cream—behave in more complicated ways, and are called non-Newtonian fluids. These come in a few different types.

Shear-thinning fluids flow more readily the more force you apply to them. The classic example is ketchup: turn the bottle upside-down and you’ll be waiting all week, but give it a hard shake and the sauce becomes instantly less viscous and flows all over your burger, plate, and leg. (You shook it too hard.) On a microscopic level, ketchup is held together by a fine mesh of pectin molecules from the tomatoes, as well as xanthan gum molecules (added to prevent syneresis). When you whack it, the xanthan molecules lose their grips on each other, freeing the fluid to flow.

Shear-thickening fluids are the reverse. Mix cornstarch into a little water and slowly poke your finger into it. Then do the same but quickly. Under the greater force of the fast poke, the stuff thickens up dramatically. Microscopic corn starch particles suspended in water have time to slide past each other when they need to—until they’re pushed too hard and traffic-jam together, slowing the flow of the whole mixture.

Then there are materials that slowly thicken or thin more the longer they’re under force: rheopectic and thixotropic fluids respectively. Hold an open jar of low-fat mayo upside-down. For a long while, nothing happens, as cumulative stress builds up. Then suddenly it’s the dog’s lucky day: the cumulative stress thins the mayo just enough for it to slump out onto the floor. That’s thixotropy. There don’t seem to be any rheopectic foods, but some engineered rheopectic fluids are used as fillings for body armor. They’re flexible until they absorb a blow, then they instantly get rigid, and only gradually soften up again.

Then you’ve got viscoelastic materials, like bread dough. When you apply force to one of these, it flows somewhat but also stretches somewhat and springs back to where it was.

Phew. Now if you think viscosity is surprisingly complicated, just wait till we get to rheology.

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Graphics by Sophie Greenspan.

As the fat warms up, it turns from solid to liquid, which starts the oozing process. At the same time, heat makes the proteins loosen their gentle hold on each other, easing into a slouchy matrix that stretches along with the now-runny emulsion. The water in the cheese stays juicily mingled with the fat. Perfect.

Alas, not all cheese melts as graciously as Jack. A sharp, long-aged Gruyère, for instance, will tend to separate into a lumpy, chewy blob of protein sitting in a pool of liquid fat. Not perfect.

The reason? Over the months that the Gruyère was aging, much of its water evaporated. That concentrated the cheese’s wonderful flavor—one reason we love aged cheeses—and bumped up its relative fat content. An emulsion is a delicate thing, and with less water present to hold up its side of the arrangement, the fat is much more likely to break out of its emulsified state and puddle up when melted. Moreover, aging also causes the cheese’s proteins to clump in little compact groups. Those tightly clustered tangles of aged proteins are too wrapped up in each other to emulsify well, and because they’re so intertwined, they don’t come apart nearly as easily when heated. Instead, they stay put while the fat melts and drips out around them.

The creators of smooth processed cheeses like Velveeta or American cheese have a solution: a salt solution. Sodium citrate is the best known of a few different ingredients known as melting salts, which facilitate the melting of old or stubborn cheeses. It’s a white powder with a salty-sour taste, but in cheese, its taste isn’t noticeable. The tight-knit proteins that hinder smooth melting are bonded to each other with the help of calcium ions. When you warm up a mixture of cheese with the addition of liquid and a small amount of sodium citrate, the sodium substitutes itself for some of the calcium that’s helping the proteins cling. As the cheese is heated, the proteins separate from each other and again act as emulsifiers, strengthening the emulsion by holding fat and water together.

The result is a stable, smooth melt with no lumps and no leaks—perfect for fondues and cheese sauces. The chemical formula for sodium citrate even spells out “nacho”. Behold: