Making your grill (or broiler) shine this summer

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BY W. WAYT GIBBS
Associated Press

Compared to other basic cooking techniques, grilling is hard: the temperatures are high, timing is crucial and slight differences in the thickness or wetness of the food can dramatically affect how quickly it cooks.

Bad design choices by equipment makers—kettle-shaped grills with black interiors, for example—make it harder still. But if you’re willing to do some simple arithmetic or break out a roll of foil, you can reduce the guesswork and get better performance from your grill. Similar tricks work for broiling; after all, a broiler is basically just an inverted grill.

Every grill has a sweet spot where the heat is even. You know you’re cooking in the sweet spot when all of the food browns at about the same pace. In most situations, the bigger the sweet spot, the better. One notable exception is when you need to reserve part of the grill for cooking some ingredients more slowly or keeping previously cooked food warm.

If you find yourself continually swapping food from the center of your grill with pieces at the periphery, that’s a sure sign that your sweet spot is too small.

You can get an intuitive feel for where the edge of the sweet spot lies by looking at the heat from the food’s point of view. I mean that literally: imagine you are a hotdog lying facedown on the grill. If the coals or the gas flames don’t fill your entire field of view, then you aren’t receiving as much radiant heat as your fellow wiener who is dead-center over the heat source. If the falloff in the intensity of the heat is greater than about 10 percent, you’re outside the sweet spot.

You can use the table below to estimate the size of the sweet spot on your own grill. The 26-inch-wide gas grill on my deck has four burners with heat-dispersing caps that span about 23 inches. The food sits only three inches above the burner caps, so when all four burners are going, the sweet spot includes the middle 16 inches of the grill. But if I use only the two central burners, which are 10 inches from edge to edge, the sweet spot shrinks to a measly 5.4 inches, too small to cook two chicken breasts side by side. I can use this to my advantage, however, if I have a big piece of food that is thick in the middle and thinner at the ends, such as a long salmon fillet. By laying the fish crosswise over the two burners, I can cook the fat belly until it is done without terribly overcooking the slimmer head and tail of the fillet.

Sweet spots are narrowest on small grills, such as little braziers, kettles, hibachis, and the fixed grilling boxes at a public parks. If the sweet spot on your grill is too confining for all the food you have to cook, you can enlarge it in several ways.

If the grill height is adjustable, lower it. Bringing the food a couple inches closer to the heat can easily expand the sweet spot by 2 to 3 inches. The effect on the intensity of the heat is less than you might expect: typically no more than about a 15 percent increase.

If your grill is boxy in shape, line the sides with foil, shiny side out. Your goal is to create a hall of mirrors in which the heat rays bounce off the foil until they hit the food. A hotdog at the edge of the grill then sees not only those coals that are in its line of sight, but also reflections of the coals in the foil-lined side of the grill.

The foil trick unfortunately doesn’t work well on kettle grills because their rounded shape tends to bounce the radiant heat back toward the center instead of out to the edges. But if you can find a piece of shiny sheet metal about 4 inches wide and 56 inches long, you can bend the metal into a reflective circular ring and build the coal bed inside of it. All food within the circumference of the ring should then cook pretty evenly.

Jury-rigging a grill in this way wouldn’t be necessary if grills came shiny on the inside and we could keep them that way. But, presumably because nobody likes to clean the guts of a grill, the interiors of most grills are painted black, the worst possible color for a large sweet spot. A black metal surface doesn’t reflect many infrared heat rays; instead it soaks them up, gets really hot, then re-emits the heat in random directions.

Someday, some clever inventor will come up with a self-cleaning grill that has a mirror finish inside, and the sweet-spot problem will simply vanish.

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HOW BIG IS YOUR SWEET SPOT?

For grills, measure the width of the coals or gas burners (including any burner caps that disperse the heat). Then measure the distance from the top of the coals or burners to the upper surface of the grill grate. Find the appropriate row in the table to estimate the size of the sweet spot, centered over the heat source. This table assumes a nonreflective grill.

To calculate the sweet spot of an electric broiler — which is the ideal vertical distance between the top of the food and the broiler element — measure the distance between the rods of the heating element. Multiply that measurement by 0.44, then add 0.2 inches to the product. For example, if the rods are 2.4 inches apart, the sweet spot is 1.25 inches from the element to the top of the food.

Width of heat source (inches) Height of the food above the heat source (inches) Width of grill sweet spot (inches)
14 3 8.1
14 4 7.7
14 5 7
16 3 9.9
16 4 9
16 5 8.3
20 3 13.2
20 4 12
20 5 11.20
23 3 16.1
23 4 15
23 5 13.3
29 3 21.8
29 4 19.7
29 5 18.9

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Photo credit: Ryan Matthew Smith / Modernist Cuisine, LLC

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

A shocking (and hot!) tip for preserving produce

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By W. WAYT GIBBS
Associated Press

Nothing is more frustrating than finding the perfect cucumber or head of lettuce at the farmers market, paying top-dollar for it, and then… tossing it out a week later when it has gone moldy or slimy in the refrigerator.

No doubt one reason so many of us eat too many convenience foods and too few fruits and vegetables is that it can be hard to get our busy schedules in sync with the produce we bring home with the best of intentions.

Food scientists, however, have discovered a remarkably effective way to extend the life of fresh-cut fruits and vegetables by days or even a week. It doesn’t involve the chlorine solutions, irradiation or peroxide baths sometimes used by produce packagers. And it’s easily done in any home by anyone.

This method, called heat-shocking, is 100 percent organic and uses just one ingredient that every cook has handy – hot water.

You may already be familiar with a related technique called blanching, a cooking method in which food is briefly dunked in boiling or very hot water. Blanching can extend the shelf life of broccoli and other plant foods, and it effectively reduces contamination by germs on the surface of the food. But blanching usually ruptures the cell walls of plants, causing color and nutrients to leach out. It also robs delicate produce of its raw taste.

Heat-shocking works differently. When the water is warm but not scalding – temperatures ranging from 105 ˚F to 140 ˚F (about 40 C to 60 C) work well for most fruits and vegetables – a brief plunge won’t rupture the cells. Rather, the right amount of heat alters the biochemistry of the tissue in ways that, for many kinds of produce, firm the flesh, delay browning and fading, slow wilting, and increase mold resistance.

A long list of scientific studies published during the past 15 years report success using heat-shocking to firm potatoes, tomatoes, carrots, and strawberries; to preserve the color of asparagus, broccoli, green beans, kiwi fruits, celery, and lettuce; to fend off overripe flavors in cantaloupe and other melons; and to generally add to the longevity of grapes, plums, bean sprouts and peaches, among others.

The optimum time and temperature combination for the quick dip seems to depend on many factors, but the procedure is quite simple. Just let the water run from your tap until it gets hot, then fill a large pot of water about two-thirds full, and use a thermometer to measure the temperature. It will probably be between 105 ˚F and 140 ˚F; if not, a few minutes on the stove should do the trick. Submerge the produce and hold it there for several minutes (the hotter the water, the less time is needed), then drain, dry and refrigerate as you normally would.

Researchers still are working out the details of how heat-shocking works, but it appears to change the food in several ways at once. Many of the fruits and vegetables you bring home from the store are still alive and respiring; the quick heat treatment tends to slow the rate at which they respire and produce ethylene, a gas that plays a crucial role in the ripening of many kinds of produce. In leafy greens, the shock of the hot water also seems to turn down production of enzymes that cause browning around wounded leaves, and to turn up the production of heat-shock proteins, which can have preservative effects.

For the home cook, the inner workings don’t really matter. The bottom line is that soaking your produce in hot water for a few minutes after you unpack it makes it cheaper and more nutritious because more fruits and veggies will end up in your family rather than in the trash.

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HEAT-SHOCKING GUIDELINES

The optimal time and temperature for heat-shocking fruits and vegetables varies in response to many factors – in particular, whether they were already treated before purchase. Use these as general guidelines.

– Asparagus: 2 to 3 minutes at 131 ˚F (55 ˚C)

– Broccoli: 7 to 8 minutes at 117 ˚F (47 ˚C)

– Cantaloupe (whole): 60 minutes at 122 ˚F (50 ˚C)

– Celery: 90 seconds at 122 ˚F (50 ˚C)

– Grapes: 8 minutes at 113 ˚F (45 ˚C)

– Kiwi fruit: 15 to 20 minutes at 104 ˚F (40 ˚C)

– Lettuce: 1 to 2 minutes at 122 ˚F (50 ˚C)

– Oranges (whole): 40 to 45 minutes at 113 ˚F (45 ˚C)

– Peaches (whole): 40 minutes at 104 ˚F (40 ˚C)

– Strawberries: 15 seconds at 140 ˚F (60 ˚C)

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Photo credit: AP Photo/Modernist Cuisine, LLC, Chris Hoover

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.

Vacuum-Concentrating, Part 1

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The Lower, the Better

Concentrating flavor is one of the most basic yet important tasks in cooking. From a technical point of view, concentrating generally means evaporating off a solvent while leaving behind as many flavorful molecules as possible. In the kitchen, the solvent is usually water, but sometimes is alcohol. Rarely is it anything else; although fats and oils are edible solvents, you’ll create a spectacular fire if you try to vaporize them.

The traditional way of concentrating flavors relies on heating the liquid to its boiling point.

To get the job done in any reasonable length of time, you must raise the temperature of the solvent to very near its boiling point. The downside to this is that water boils at about 100 °C / 212 °F (the exact temperature varies with altitude and weather conditions), which is often hot enough to dramatically alter many of the flavors you’re trying to concentrate. Sometimes those alterations are exactly what you want: simmering a meat stock for hours plays a crucial role in creating the rich flavor of a traditional demi-glace, for example. But in many cases, the new flavors aren’t so delicious. As a rule of thumb, foods that people usually eat raw are likely to suffer from the high temperatures that reduction requires. When you concentrate an orange juice, for instance, you lose its vibrancy, and it ends up tasting like… well, cooked orange juice.

It turns out there is an alternative way to concentrate these delicate kinds of flavors without ruining them. Increasing pressure raises the boiling point of water (as happens in a pressure cooker), and conversely decreasing pressure lowers the boiling point of water. So the lower the pressure (the stronger the vacuum), the lower the boiling point. In fact, it’s entirely possible to reduce the pressure so far that ice-cold water will boil. A couple years ago in our research kitchen, we used a chamber vacuum sealer to freeze liquid nitrogen solid!

A rotary evaporator offers unparalleled flexibility in creating vacuum-concentrated juices and sauces.

When talking about vacuum pressure, it’s both convenient and illustrative to quantify the pressure in units of millibars (mbar). At sea level, the standard atmospheric pressure is 1,013.25 mbar and the boiling point of water is 100 °C / 212 °F. Take a trip to the mile-high city of Denver and the pressure drops to 805 mbar, and water boils at 93.7 °C / 200.7 °F. That’s not too great a difference, but a vacuum-concentration setup can reduce the pressure surrounding your pot of liquid all the way down to 55 mbar, enough for it to come to a boil at the perfectly pleasant room temperature of 20 °C / 68 °F. That moderate temperature will not destroy any delicate and fresh-smelling aroma compounds.

And more of those compounds will stay in the food, rather than being flung into the air as happens during traditional stove-top reduction. Now it’s true that lowering the boiling point of water also lowers the boiling point of other volatile molecules, so even vacuum reduction does throw away some of those aromas (which make the kitchen smell so nice). But more of them will remain where you want them–flavoring the food–than if you just turn up the burner to drive off the liquid.

It’s easy to imagine all kinds of dishes that benefit from flavors concentrated at low temperatures. At The Cooking Lab, we vacuum-concentrate granny smith apple juice, to preserve its fresh, tart flavor as well as its bright green appearance. Vacuum-reduced wine-based sauces are also interesting because you can boil out both the ethanol and water at very mild temperatures. Personally, I like to use a simple setup I have at home to prepare cocktails with vacuum-concentrated infusions and tinctures.

The results are always very different than anything you’ve had before. Actually, it’s a bit hard to describe these flavor profiles because few people have tasted anything like them before. Until now no one has come up with an easy way to vacuum-concentrate in the kitchen.

In my next post, I’ll show you how to build your own relatively simple and inexpensive vacuum-concentrating setup with the help of a little Google-fu. In the meantime, check out the table below for a range of concentrating strategies, all of which are covered in Modernist Cuisine. (Click on the table for a larger version suitable for printing.)

Torch Tastes

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In response to my recent post on “doneness,” reader Rusty Shackleford posted the following question: “When using my blow torch, sometimes I notice unpleasant propane tastes. Anything you can tell me about general blow torch cooking?”
Blowtorch Searing Short-Rib
This brought to mind a similar question that I was recently asked about the use of other flammable gases in cooking. As is often the case at The Cooking Lab, one question leads to another and before I knew it, my short answer had grown beyond the scope of the original question. We cover the topic more extensively in the book, but here is a brief description of how the use of a blow torch and the type of gas therein can affect the flavor.

Natural gas (methane) is a common fuel for ranges and stovetops, but most torches used for cooking are fueled by propane or butane. Fuels like oxyacetylene and MAPP gas, however, typically burn hotter and thus can impart a larger amount of heat to the food for a faster sear.

The type of gas that you choose isn’t as important as the completeness of its combustion. Propane, butane, MAPP, and acetylene are all great so long as you adjust the flame of the torch so that it is a fully oxidizing flame. This is a flame that is produced with an excess of oxygen, either from the surrounding air or supplemented with compressed oxygen. You can tell that you have an oxidizing flame when the torch is burning dark blue, is relatively short in length, and hisses and roars. Frequently, people have too large of a flame that is burning yellow at the tip. This is a reducing flame, also referred to as a carburizing flame because there are uncombusted hydrocarbons from the fuel in the flame that will end up in the food, imparting an unpleasant taste. In my experience, butane torches are especially prone to this, but it can happen with any torch that hasn’t been properly adjusted before aiming it at the food.

Too often, people aim the blow torch at the food before they have it appropriately adjusted. Not only do they often end up torching the food with a dirty flame, but there is also some raw fuel being blown onto the food before it ignites. Like an old, carbureted car (and for the same reason), it is best to light the torch and adjust the fuel-to-oxidizer ratio before getting underway.

Long story short, always light your torch facing away from the food. Then adjust the torch to produce a short, hissing dark blue flame and you won’t have a problem.