Why food goes from almost done to overdone so quickly on the grill

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BY W. WAYT GIBBS
Associated Press

Ever tried toasting hamburger buns on a grill? It takes uncanny timing to achieve an even medium brown across the buns. Typically, they remain white for what seems like far too long. Then it’s as if time accelerates, and they blow past toasted to burnt in the time it takes to flip the burgers.

Barbeque_Hamburger Cutaway_VQ6B8473 With LAYERS

The same phenomenon is at work when you toast a marshmallow over a campfire: wait and turn, wait and turn… then brown, black and — poof! — it’s aflame. The problem is perhaps most acute when cooking shiny-skinned fish on a grill or under a broiler. Once the skin turns from silver to brown, the heat pours into the fillet, and the window of opportunity for perfect doneness slams shut with amazing speed.

Anytime you cook light-colored food with high heat, inattention is a recipe for disaster. But the physics here is pretty simple, and once you understand it you can use several methods to improve your odds of making that perfectly toasted bun, golden half-melted marshmallow, or juicy grilled fillet.

At high temperatures — about 400 F (200 C) and up — a substantial part of the heat that reaches the food arrives in the form of infrared light waves rather than via hot air or steam. The higher the temperature, the bigger the part that radiant heat plays in cooking. But this form of heat interacts with color in a profound way.

The bottom of a hamburger bun looks white because it reflects most of the visible light that hits it, and the same is true for infrared heat rays. There is a reason that white cars are popular in Phoenix — they stay cooler in the sunshine, which is full of infrared radiation.

A silvery, mirror-like fish skin is even more reflective than a white car. About 90 percent of the radiant heat striking it simply bounces away. Because only around 10 percent of the energy sinks in and warms the fish, cooking initially creeps along slowly but steadily.

That changes rapidly, however, as soon as the food gets hot enough to brown. It’s like changing from a white shirt to a black shirt on a sunny summer day. As the food darkens, that 10 percent of energy absorbed rises by leaps and bounds, and the temperature at the surface of the food soars.

So browning accelerates, which increases heat absorption, which boosts the temperature; it’s a vicious circle. By the time you can get a spatula under the fillet to flip it over, it may be almost black, reflecting just 10 percent of the heat and sucking in 90 percent.

There are at least three ways around this problem. The simplest is to stare, hawk-like, at the food and lower or remove the heat as soon as browning starts. That works fine for marshmallows but is not always practical in the kitchen or backyard barbecue.

In some cases, you can darken the color of the food at the start, for example by slathering it with a dark sauce or searing it in a very hot skillet before putting it on the grill. This is a way to make a fish steak cook more like a beef steak, which is fairly dark even when raw and so doesn’t experience such a dramatic shift in heat absorption. This method generally shortens the cooking time.

Finally, try piling other ingredients, such as sliced onions or zucchini, between the food and the coals or the broiler element to moderate the intensity of the radiant heat. Cooking times will lengthen — and you may end up having to toss out the sacrificial buffer ingredients if they get charred — but that window of opportunity will stay open longer.

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Photo credit: Ryan Matthew Smith / Modernist Cuisine, LLC

Science helps craft the perfect mac and cheese

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BY SCOTT HEIMENDINGER
Associated Press

Imagine your favorite cheese: perhaps an aged, sharp cheddar, or maybe a blue Gorgonzola or a gentle Monterey Jack. Wouldn’t it be wonderful to use those really good cheeses you love on nachos or as a sauce on macaroni or steamed vegetables?

But if you have ever tried melting high-quality cheeses, you’ve experienced the problem: the cheese separates into a greasy oil slick that no amount of stirring will restore.

One traditional workaround is to make a Mornay sauce, which combines the cheese with a cooked mixture of flour, butter and milk. But a Mornay sauce can end up tasting as much of cooked flour as it does of cheese. The starch in the flour actually masks some of the flavors in the cheese, so the sauce loses its vibrancy.

A clever Canadian-born cheesemaker in Chicago discovered a much better solution around 1912. His name may ring a bell — James L. Kraft.

Kraft found that adding a small amount of sodium phosphate to the cheese as it melted kept it from turning into a clumpy mess of cheese solids swimming in a pool of oil. Kraft patented his invention and used it to make canned, shelf-stable cheese. He sold millions of pounds of the stuff to the American military during World War I. The technique ultimately led to the creation of Velveeta and a whole universe of processed cheese products.

You can apply the very same chemistry, however, to achieve much higher culinary purposes. The chefs in our research kitchen have made mac and cheese with an intense goat gouda and cheddar sauce, for example, and build gourmet grilled cheese sandwiches using cheese slices that melt like the processed stuff, but are made from feta or Stilton.

In place of sodium phosphate, we use sodium citrate, which is easier to find in grocery stores or online. Like sodium phosphate, sodium citrate is an emulsifying salt that helps tie together the two immiscible components of cheese: oil and water.

In solid form, cheese is a stable emulsion. The tiny droplets of dairy fat are suspended in water and held in place by a net of interlinked proteins. When cheese melts, however, that net breaks apart, and the oil and water tend to go their separate ways. Sodium citrate can form attachments to both fat and water molecules, so it holds everything together. The end result is a perfectly smooth, homogeneous sauce. The sauce even can be cut into processed cheese-like slices once it cools.

When making cheese sauce, we add 4 grams of sodium citrate for every 100 grams of finely grated cheese and 93 grams of water or milk. To make cheese slices, we reduce the amount of water to about 30 grams (cold wheat beer works very well, too), pour the melted mixture into a sheet pan, and let it solidify in the refrigerator for about two hours before cutting it into pieces, which then can be wrapped in plastic and frozen.

Because this method of stabilizing melted cheese bypasses all of the flour, butter and milk used in Mornay sauce, the resulting cheese sauce is much richer; a little goes a long way. But the sauce keeps well in the refrigerator and reheats nicely in the microwave, so save any extra and use it to top vegetables, nachos or pasta.

For our Mac and Cheese recipe, click here.

Photo credit: Melissa Lehuta / Modernist Cuisine, LLC

The Maillard Reaction

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One of the most important flavor-producing reactions in cooking is the Maillard reaction. It is sometimes called the “browning reaction” in discussions of cooking, but that description is incomplete at best. Cooked meats, seafood, and other protein-laden foods that undergo the Maillard reaction do turn brown, but there are other reactions that also cause browning. The Maillard reaction creates brown pigments in cooked meat in a very specific way: by rearranging amino acids and certain simple sugars, which then arrange themselves in rings and collections of rings that reflect light in such a way as to give the meat a brown color.

The important thing about the Maillard reaction isn’t the color, it’s the flavors and aromas. Indeed, it should be called “the flavor reaction,” not the “browning reaction.” The molecules it produces provide the potent aromas responsible for the characteristic smells of roasting, baking, and frying. What begins as a simple reaction between amino acids and sugars quickly becomes very complicated: the molecules produced keep reacting in ever more complex ways that generate literally hundreds of various molecules. Most of these new molecules are produced in incredibly minute quantities, but that doesn’t mean they’re unimportant.

The Maillard reaction occurs in cooking of almost all kinds of foods, although the simple sugars and amino acids present produce distinctly different aromas. This is why baking bread doesn’t smell like roasting meat or frying fish, even though all these foods depend on Maillard reactions for flavor. The Maillard reaction, or its absence, distinguishes the flavors of boiled, poached, or steamed foods from the flavors of the same foods that have been grilled, roasted, or otherwise cooked at temperatures high enough to dehydrate the surface rapidly — in other words, at temperatures above the boiling point of water. These two factors, dryness and temperature, are the key controls for the rate of the Maillard reaction.

High-temperature cooking speeds up the Maillard reaction because heat both increases the rate of chemical reactions and accelerates the evaporation of water. As the food dries, the concentration of reactant compounds increases and the temperature climbs more rapidly.

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Temperatures need to be high to bring about the Maillard reaction, but as long as the food is very wet, its temperature won’t climb above the boiling point of water. At atmospheric pressure, only high-heat cooking techniques can dry out the food enough to raise the temperature sufficiently. It’s not the water that stops the reaction, but rather the low boiling point at normal, sea-level pressure. In the sealed environment of a pressure cooker, the Maillard reaction can, and does, occur. This is something we exploit when making soups, like in our Caramelized Carrot Soup, or purees, like the broccoli puree in our Brassicas recipe. Adding baking soda to the pressure cooker raises the food’s pH (making it more alkaline), which also helps. Chinese cooks often marinate meat or seafood in mixtures containing egg white or baking soda just before stir-frying.

So, in boiled, poached, and steamed muscle foods, an entirely different set of aromas dominates the flavor. Drying and browning the surface first will, however, allow the reaction to proceed slowly at temperatures below the boiling point of water. This is why we sear frozen steak before cooking it in a low-temperature oven. Searing food before vacuum sealing and cooking sous vide can add depth to the flavor of sous vide dishes. This step should be avoided for lamb, other meats from grass-fed animals, and a few other foods in which presearing can trigger unwanted reactions that cause off-flavors and warmed-over flavors to form when the food is later cooked sous vide. We recommend searing those foods after cooking them sous vide.

Blowtorch-cropped

One of the challenges to getting the Maillard reaction going is getting the surface hot and dry enough without overcooking the underlying flesh, or at least overcooking it as little as possible. Cooks have developed several strategies to this end, some simple and some fairly baroque.

One strategy that works well is to remove as much water from the surface of the meat as possible before cooking it (via blotting or drying at low temperature). Fast heating using deep fryers, super-hot griddles and grills, and even blowtorches are also helpful tactics, such as when we deep-fry chicken wings.

You might think that raising the temperature even higher would enhance the Maillard reaction. It does up to a point, but above 180 °C / 355 °F a different set of reactions occur: pyrolysis, also known as burning. People typically like foods a little charred, but with too much pyrolysis comes bitterness. The black compounds that pyrolysis creates also may be carcinogenic, so go easy on charring your foods for visual appeal.

Adapted from Modernist Cuisine

Is It Safe to Cook with Plastic?

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Since writing Modernist Cuisine and Modernist Cuisine at Home, we’ve been asked many times to comment on the safety of cooking in plastic bags. Many of our sous vide recipes, from our Sous Vide Salmon and Rare Beef Jus to our Cranberry Consommé and Scrambled Egg Foam, require vacuum-sealing or using a zip-top bag. Similarly, many of our recipes that utilize microwaves, such as our Microwaved Tilapia, Eggplant Parmesan, and Microwave-Fried Herbs, require plastic wrap.

According to the latest research, the safest plastics for use with food are high-density polyethylene, low-density polyethylene, and polypropylene. Virtually all sous vide bags are made from these plastics, as are most brand-name food storage bags and plastic wraps such as Saran wrap. Polyethylene is widely used in containers for biology and chemistry labs, and it has been studied extensively. It is safe.

Less expensive, bulk plastic wraps sold to the catering trade are not as safe, however. These products are commonly made from polyvinyl chloride (PVC), which can contain harmful plasticizers that have been shown to leach into fatty foods such as cheese, meat, and fish. Legitimate concerns exist about food exposed to these plastics at high temperatures. Polyethylene-based plastic wraps are available at only slightly higher costs and do not raise such concerns. An easy way to spot the difference is to check that your cling wraps or plastic bags are rated microwave-safe. Bags and wraps made form polyethylene are generally microwave-safe, whereas those that contain polyvinyl chloride plastics generally are not.

Many professional kitchens use clear, rigid, plastic storage containers that are made from polycarbonate. While they are currently approved for food use, these plastics also may be a cause for concern because they contain bisphenol A (BPA), a chemical that can disrupt hormone activity and leach into foods and beverages. Cracks and crazing due to wear and tear increase the rate at which BPA leaches out of polycarbonates.

The bottom line is that bags made expressly for cooking sous vide are perfectly safe—as are oven bags, popular brands of zip-top bags, and stretchy plastics such as Saran wrap. If you remain hesitant to try cooking sous vide due to concerns over plastic, you can always use canning jars instead, but beware that cooking times will be longer.

—Adapted from Modernist Cuisine and Modernist Cuisine at Home

Why Cook Sous Vide?

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Cooking sous vide is easier than its fancy name might suggest. You simply seal the ingredients in a plastic bag (you can also use a canning jar) and place them in a water bath, a combi oven, or any other cooker that can set and hold a target temperature to within a degree or two. When the food reaches your target temperature or time, you take it out, give it a quick sear or other finish, and serve it. That’s it.

The sous vide method yields results that are nearly impossible to achieve by traditional means. In the photo above, both of the tenderloins started at the same weight. The steak on the left was cooked in a pan to a core temperature of 52 °C / 126 °F, but more than 40% of the meat was overcooked. The other steak was cooked sous vide to the same temperature and then seared with a blowtorch to yield a juicier steak that is done to perfection from edge to edge.

Similarly, beef short ribs braised at 58 °C / 136 °F for 72 hours are melt-in-your-mouth tender, yet pink and juicy. And the delicate, custard-like texture of an egg poached at precisely 65 °C / 149 °F is amazing.

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Sous vide is especially useful for cooking meats and seafood, for which the window of proper doneness is often vanishingly small when traditional methods are used. When you fry a piece of fish, the flesh is most succulent and tender within a very narrow temperature range. Because the cooking temperature of the pan is at least 200 °C / 392 °F hotter than the ideal core temperature of the fish, the edges will inevitably be far more cooked than the center when pan-fried.

Chicken breasts and other poultry cuts and poultry products are often held at a target temperature for a different reason: to kill potential pathogens and improve the safety of the food.

The idea of preserving and cooking food in sealed packages is ancient. Throughout culinary history, food has been wrapped in leaves, potted in fat, packed in salt, or sealed inside animal bladders before being cooked. People have long known that isolating food from air, accomplished more completely by vacuum sealing, can arrest the decay of food. Packaging food also prevents it from drying out.

Although sous vide literally means “under vacuum” in French, the defining feature of the sous vide method is not packaging or vacuum sealing; it is accurate temperature control. A computer-controlled heater can warm a water bath to any low temperature you set, and it can keep it there for hours, or even days, if needed.

Such mastery over heat pays off in several important ways, most notably, freeing the cook from the tyranny of the clock. Traditional cooking with a range, oven, or grill uses high and fluctuating temperatures, so you must time the cooking exactly; there is little margin for error. With just a moment’s inattention, conventional cooking can quickly overshoot perfection.

When cooking sous vide, in contrast, most foods will taste just as good even if they spend a few extra minutes at a target temperature, so you can relax and devote your attention to the more interesting and creative aspects of cooking.

Precise temperature control and uniformity of temperature has two other big advantages. First, it allows you to cook food to an even doneness all the way through, no more dry edges and rare centers. Second, you get highly repeatable results. The steak emerges from the bag juicy and pink every time.

A final important benefit is that the closed bag creates a fully humid environment that effectively braises the food, so ingredients cooked this way are often noticeably juicier and more tender. Food cooked sous vide doesn’t brown, but a simple sear adds that traditional flavor where needed so that you can have the best of both worlds.

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We’ve been asked many times about the safety of cooking plastic bags. The bottom line is that bags made expressly for cooking sous vide are perfectly safe, as are oven bags, popular brands of zip-top bags, and stretchy plastic wrap such as Saran Wrap.

The plastic that these products are made of is called polyethylene. It is widely used in containers for biology and chemistry labs, and it has been studied extensively. It is safe. But, do avoid very cheap plastic wraps when cooking. These are made of polyvinyl chloride (PVC), and heating them presents a risk of chemicals leaching into the food.

Cooking sous vide isn’t complicated or expensive. In Modernist Cuisine at Home, we guide you through the various kinds of sous vide equipment and supplies available for home cooks, including how to improvise your own setup. Check back later in the week when we share such methods using equipment you probably already own.

 

— Adapted from Modernist Cuisine at Home and Modernist Cuisine

The Physics of Coffee & Cream

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Every Seattleite has been in this situation: On a cold, rainy December morning, you get your coffee to go from Vivace, Stumptown, or Starbucks, and then watch out the window for your bus. The bus, you know, might be a minute or two late, and you’ll have to wait a few minutes. You want to keep your coffee as hot as possible during your wait so that it’s still piping hot when you step out the door. You grab a lid for your cup, pausing at the cream. Should you add the cream to your coffee now, or will that only cool your drink faster? Maybe you should add your cream at the last minute, before you dash out the door.

The basic physics of heat provides the answer: you should go ahead and add the cream to your coffee now. Coffee with cream cools about 20% slower than black coffee, for three reasons:

  1. Black coffee is darker. Dark colors absorb heat faster than light colors (just think about wearing a black T-shirt versus a white T-shirt on a hot, sunny day). But dark colors also emit heat faster than light colors—absorption and emission are essentially two sides of the same coin. So by lightening the color of your coffee, you slow its rate of heat loss slightly.
  2. Stefan-Boltzmann says so. The Stefan-Boltzmann law says that hotter surfaces radiate heat faster—specifically, the power of emission is proportional to the temperature (in kelvin) raised to the fourth power. So let’s say you have two cups of coffee that start at the same temperature. You pour cream in cup #1 and the coffee drops in temperature immediately. But the rate at which it loses heat also drops. Meanwhile, the hotter black coffee in cup #2 cools so rapidly that within five minutes the two coffees are at about the same temperature. But you still haven’t added the cream to coffee #2! When you do, it cools even more; cup #1 is now the hotter of the two.
  3. Viscosity versus evaporation. This is the clincher. Adding cream thickens the coffee (adds viscosity), so it evaporates slower. You’d be surprised just how much heat evaporation carries away. Slow the rate of evaporation and you avoid a lot of that heat loss. (This is also one big reason that coffee stays warm longer with a lid on the cup.)

So, next time you’re caught in the rain, put the cream in your coffee right away. Your fingers will thank you.

Watch our high-speed video above of cream being poured into coffee at 2,000 frames per second.

Our Guide to Picking the Perfect Pan

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Are you looking for a new set of pans this holiday season? Scott Heimendinger, our Director of Applied Research, explains the science behind heat diffusion in stove-top cooking on MDRN KTCHN on CHOW.com. The end result: Thickness is more important than material, no matter how shiny and expensive those copper pans may be. He also gives you a few work-arounds for uneven stoves.

Watch Nathan’s Modernist Cuisine Story on NOVA scienceNOW

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Last night, NOVA scienceNOW aired “Can I Eat That?,” a show on the science of food and cooking, which profiled Nathan Myhrvold in the final segment. Host David Pogue narrates a behind-the-scenes look at Nathan’s inspiration for creating Modernist Cuisine and Modernist Cuisine at Home. For those of you interested in seeing The Cooking Lab’s equipment, how the cutaway photos were made, or what Nathan looked like as a kid, we think you’ll enjoy this. It is a great illustration of the story of Modernist Cuisine.

The Chemistry of the Barbecue “Stall”

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The “stall” is widely known among serious barbecuers. Well into cooking, the temperature of uncovered meat stops rising and may even fall slightly before it climbs again. Most barbecue experts say this stall occurs when connective tissue in the meat softens and fat starts to render, which does occur, but it doesn’t cause the stall.

The stall is quite real, but it is not due to softening collagen as the graph below shows. We cooked two briskets side-by-side in a convection oven, which mimicked the air temperature in a smoker, but was much more consistent and thus better suited for the experiment. We left one brisket uncovered (blue curve) and vacuum sealed the other (green curve). Sensors measured the core temperature of each brisket as well as the dry-bulb (black curve) and wet-bulb (red curve) air temperatures in the oven.

The stall clearly occurred in the uncovered brisket 2-4 hours into cooking as the wet-bulb temperature in the oven fell. The stall ended after about four hours because the surface of the brisket had dried out enough that it was above the wet-bulb temperature. The temperature of the vacuum-sealed brisket, in contrast, rose steadily to the oven’s set point in about three hours. Any effect due to collagen or fat rendering would occur in both briskets, but we see the stall only in the uncovered one.

Early in the cooking, the wet-bulb temperature rose as the uncovered brisket evaporated, increasing the relative oven humidity to about 72%. But the humidity then began to drop as evaporation could no longer keep pace with the air venting out of the oven. By the eight-hour mark, the humidity was below 50%, and the wet-bulb temperature was down almost 10 °C / 18 °F from its peak.

The core of the uncovered brisket stalled. In this test, we left the brisket dry, but if we had slathered it with sauce periodically as many barbecue chefs do, we could prolong the stall by keeping the surface wet.

Sous vide cooking is, in our opinion, by far the best way to achieve the perfect cooking rate necessary for great barbecue. We barbecued in two distinct steps: smoking to impart the smoke flavor, followed by sous vide cooking to achieve the optimum texture and done-ness.

Smoking before a long sous vide cooking step has the advantage of proteins remaining intact and able to react readily with smoke. Smoked food continues to change while being cooked sous vide: its pellicle darkens, the rind becomes firmer, and the smoky flavor mellows.

The alternative, of course, is to smoke the food after cooking it sous vide. This also works well, but a longer smoking time is required to develop a robust smoked flavor and appearance. This is because precooking denatures a large fraction of the proteins in a cut of meat or a piece of seafood, which leaves the flesh less reactive to the smoke.

Whichever approach you choose to take and you should try both ways to judge the differences yourself the remarkable texture that is the hallmark of sous vide cooking, and the consistency it brings to smoking, makes it the best way to smoke meats and seafood. Alternatively, you could substitute for the sous vide step a combi oven, CVap oven, or low-temperature steamer.

You can find our recipe for Smoked Dry-Rub Pork Ribs here.

–This post was adapted from Modernist Cuisine. Too see what others think of our pastrami, see the Steven Colbert clip below, and click here to read about what Steven Raichlen has to say on The Barbecue Bible.

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Nathan Myhrvold on Top Chef Tonight!

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Tonight’s episode of Top Chef will feature Modernist Cuisine author Nathan Myhrvold as a guest judge. What will they make for him? We can’t say (though the videos above are a pretty good tease!); you’ll have to tune in to find out! It’s a pretty safe bet that it will feature barbecue, one of Nathan’s passions, and probably won’t be quite as strange as the foods Nathan told Padma Lakshmi about the last time they met at the New York Academy of Science’s “Science and the City” program.

The episode will run 75 minutes and airs at 10 PM (9 Central) on Bravo.