Cooking for Geeks: Real Science, Great Hacks, and Good Food

by Jeff Potter

  I find it useful to have multiple frying pans so that I can cook different components of a dish separately. Onions (left pan), for example, are often "sweated" at a lower temperature, to keep them from caramelizing, while sausage (right pan) needs to be cooked hot enough to trigger the Maillard reactions that give seared meats an intensely rich flavor.

  Saucepans. A saucepan, roughly as wide as it is tall and with straight sides, holds two to three quarts of liquid and is used in cooking liquid foods such as sauces, small batches of soups, and hot drinks like hot chocolate. Look for a pan that has a thick base, as this will help dissipate the heat and avoid hot spots that could burn your food. Keep in mind that many of the liquids cooked in a saucepan tend to be things that can burn, so it’s worth spending a bit more to purchase a pan that conducts heat better. I picked up my favorite saucepan as an "odd lot" piece from a department store set. (Be sure to snag the lid as well!) You might prefer a saucier pan, one that has rounded corners that are easier to get into with a whisk or a spoon.

  Stockpots. A stockpot holds two or more gallons of liquid and is used in blanching vegetables, cooking pasta, and making soups. Since most applications for a stockpot involve a large amount of water, burning foods is not as much of a concern as it is with a saucepan—unless you can figure out how to burn water! The stockpot I use is one of the $20 cheap stainless steel commercial varieties. Make sure to pick up a lid as well, because commercial sellers tend to sell them separately.

  Cast iron pans. You should have a good cast iron pan in your pot and pan collection. Cast iron pans are heavy, and their larger mass allows for better retention of heat. Cast iron pans can also be heated to higher temperatures than nonstick and stainless steel pans, making them ideal for searing foods such as meat. They’re also handy for baking items such as corn-bread or deep-dish pizza. Just remember to avoid cooking highly acidic items such as tomatoes in them, because the iron will react with acidic items.

  As with frying pans, when washing cast iron, don’t use soap. Instead, rinse the pan and wipe the inside to dislodge any stuck-on food, and then place the pan back on the stove. If the food is really stuck, throw in a few tablespoons of course salt and a spoonful or two of vinegar or lemon juice, and "sand" it off with a paper towel. Once your pan is clean, wipe it down with a little heat-stable oil such as canola or sunflower oil (but not extra virgin olive oil) and place on a burner set for low heat for a minute or so to thoroughly dry it out. And never let it sit in water for hours on end, because the water will ruin the finish. If you do end up with rust spots, don’t fear. You can use a metal scrubbing brush to scrape away the rust, and then reseason the pan with a coating of oil.

  Metals, Pans, and Hot Spots

  What’s the deal with pans made of different metals or with various combinations sandwiched together? It has to do with the differences in thermal conductivity (how quickly heat energy moves through a material) and heat capacity (how much energy it takes to heat a material, which is the same as how much energy it’ll give off when cooling).

  Let’s start with the thermal conductivity of common metals in pans, along with a few other materials for reference.

  Pans made from materials with a lower thermal conductivity take longer to heat, because the thermal energy applied from the burner takes longer to transfer up and outward. In physics-speak, this is called low thermal response time. In cooking, pans with low thermal conductivity (cast iron, stainless steel) are "sluggish" in response to changes in heat. Pop them on the burner, and nothing seems to happen for a while. Likewise, if you get them too hot and pull them off the burner, food in them will continue to cook for a while.

  Given two pans of identical diameter, one cast iron and one aluminum, the aluminum pan will conduct the heat throughout the pan faster. Here’s a picture of this, using thermal fax paper (hey, not all of us can afford a thermal imaging camera!). Since thermal fax paper turns dark where heated, dark = hot and white = cold.

  Cast iron pan on a gas burner = slower heat transfer.

  Aluminum iron pan on a gas burner = faster heat transfer.

  Note

  If you’re keen to try this yourself, grab a roll of thermal fax paper, heat your pan on the burner for 30 to 60 seconds, turn off the heat, and then place a square sheet of paper on top of the pan and coat it with a few cups of cold rock/kosher salt to help press the paper against the surface of the pan.

  Notice that the gas burner has a wide radius and the gas jets are directed outward. Result? The center of the pan actually ends up being colder. The cast iron pan shows this well because the heat does not conduct through the material as quickly as it does with the aluminum pan, leading to a cold spot.

  Specific heat is important, too. Specific heat is the thermal energy (measured in joules) needed to change a unit mass of material by a unit of temperature, and it differs between materials. That is, it’ll take a different amount of energy to raise a kilogram of cast iron 1°C versus a kilogram of aluminum, because of how the materials are structured at the atomic level. How do common metals in pans compare in terms of specific heat?

  Cast iron has a lower specific heat than aluminum. It takes roughly twice as much energy (897 J/ kg*K versus 450 J/kg*K) to heat the same amount of aluminum up to the same temperature, and because energy doesn’t just disappear (first law of thermodynamics), this means that a kilogram of aluminum will actually give off more heat than a kilogram of cast iron as it cools (e.g., when you drop that big steak onto the pan’s surface).

  It’s not just the thermal conductivity or specific heat of the metal that matters, though; the mass of the pan is critical. I always sear my steak in my cast iron pan. It weighs 7.7 lbs / 3.5 kg, as opposed to 3.3 lbs / 1.5 kg in the case of my aluminum pan, so it has more heat energy to give off. When searing, pick a pan that has the highest value of specific heat * mass, so that once it’s hot, it won’t drop in temperature as much when you add the food.

  There are a few other factors you should consider when picking a pan. Cast iron and aluminum react with acids, so pans made of those materials shouldn’t be used for simmering tomatoes or other acidic items. Nonstick pans shouldn’t be heated above 500°F / 260°C. And then there are cases where the pan isn’t the primary source of heat for cooking: when boiling or steaming, the water provides the heat transfer, so the material used in making the pan isn’t important. Likewise, if you’re using an ultra-high-BTU burner (like the 60,000-BTU burners used in wok cooking), the pan isn’t a heat sink so heat capacity isn’t important.

  What’s the deal with cladded metals? You know, pans with copper or aluminum cores, encased in stainless steel or some other metal? (Clad = to encase with a covering.) These types of pans are a solution to two goals: avoiding hot spots by evening out heat quickly (by using aluminum or copper), and using a nonreactive surface (typically stainless steel, although nonstick coatings also work) so that the food doesn’t chemically react with the pan.

  Finally, if you’re buying a pan and can’t decide between two otherwise identical choices, go for the one that has oven-safe handles. Avoid wood, and make sure the handles aren’t so big that they prevent popping the pan in the oven.

  Measuring cups and scales

  In addition to the common items used for measuring (e.g., measuring cups and spoons), I strongly recommend purchasing a kitchen scale. If you will be following any of the recipes from this book using hydrocolloids or other food additives (see Chapter 6), it is practically required. You might not use it every day (or even every week), but there is no substitute for it when you need one.

  You can pour ingredients directly into a mixing bowl by weight, skipping the need for measuring cups.

  You will obtain better accuracy when measuring by weight. Dry ingredients such as flour can become compressed, so the amount of flour in "1 cup" can vary quite a bit due to the amount of pressure present when it’s packed (see the sidebar Weight Versus Volume: The Case for Weight). Also, it is easier to precisely measure weight than volume
. Because much of cooking is about controlling chemical reactions based on the ratio of ingredients (say, flour and water), changes in the ratio will alter your results, especially in baking. Weighing ingredients also allows you to load ingredients serially: add 390 grams of flour, hit tare; 300 grams of water, hit tare; 7 grams of salt, hit tare; 2 grams of yeast, mix, let rest for 20 hours, and you’ve got no-knead bread. (See the interview with Martin Lersch in Martin Lersch on Chemistry in the Kitchen in Chapter 5 for baking instructions.)

  Use a high-precision scale when working with food additives.

  When choosing a scale, look for the following features:

  A digital display, showing weights in grams and ounces, that has a tare function for zeroing out weight

  A flat surface on which you can place a bowl or dish (avoid scales that have built-in bowls)

  A scale that is capable of measuring up to at least 5 lbs or 2.2 kg in 0.05 oz or 1g increments

  If you plan on following any "molecular gastronomy / modernist cuisine" recipes that use chemicals, you’ll need to pick up a high-precision scale that measures in increments of 0.1 gram or finer. I use an American Weigh Scale AMW-100.

  Spoons & co.

  Few things symbolize cooking more than a spoon, and for good reason: stirring, tasting, adjusting the seasoning, stirring some more, and tasting again would be virtually impossible without a good spoon! I prefer the wooden variety. In an age of technology and modern plastics, there’s just something comforting about a wooden spoon. Look for one that has a straight end, as opposed to a traditional spoon shape, because the straight edge is useful for scraping the inside corners and bottom of a pan to release fond. When it comes to cleaning them, I run mine through the dishwasher. True, it’s bad for the wood, but I find it easier and don’t mind buying a new one every few years.

  Weight Versus Volume: The Case for Weight

  How much of a difference does it really make to weigh your flour? To find out, I asked friends to measure out 1 cup of all-purpose flour and then weigh it. Ten cups later, the gram weights were in: 124, 125, 131, 133, 135, 156, 156, 158, 162, and 163. That’s a whopping 31% difference between the lowest and highest measurements.

  How much flour is in a cup? Depends on whether you pack it in tight (on left: 1 cup at 156 grams, then sifted) or keep it loose (on right: 1 cup at 125 grams, then sifted).

  Even if you could perfectly measure the same weight with every cup, you still might end up using a different amount than what a recipe calls for. The average weight of the 10 samples above is 144 grams. The United States Department of Agriculture defines 1 cup of flour as 125 grams; Wolfram|Alpha (http://www.wolframalpha.com) gives 137 grams. And the side of the package of flour in my kitchen? 120 grams.

  The upshot? You’ll get better results by weighing ingredients, especially when baking. A cup might not be a cup, but 100 grams will always be 100 grams. Clearly, weight is the way to go.

  But what about wet measurements—measurements of things that don’t compress? While you’re not going to see the same variability, you can still end up with a fair amount of skew just based on the accuracy of the measuring device. The following image shows what four different methods for measuring 1 cup of liquid yielded.

  212 grams Tablespoon (16 tablespoons = 1 cup)

  225 grams Liquid measuring cup

  232 grams Dry measuring cup

  237 grams Digital scale

  Besides the ubiquitous wooden spoon, here are a few related tools that you should keep "near to hand" while cooking.

  Silicone stirring spatulas. This type of spatula, in addition to making perfect scrambled eggs, is handy for folding egg whites into batters, scraping down the edges of bowls, and reaching into the corners of pots needing stirring. Silicone is also heat-stable up to 500°F / 260°C.

  Whisks. If you’re going to bake much, a whisk is essential. Go for a standard balloon whisk, not one of those funky attempts at wires with balls on the end or crazy little loopy things. Besides coming in handy when you want to whisk eggs and dressings, you should always whisk together the dry ingredients for baked goods to ensure that things like salt and baking powder are thoroughly blended with the flour.

  Kitchen shears. Essentially heavy-duty scissors, kitchen shears are useful for cutting through bones (see Butterflied Chicken, Broiled and Roasted) and are a great alternative to a knife for cutting leafy greens, both small (chives) and large (Swiss chard). If you’re serving soup into bowls and want to garnish with chives, instead of using a knife and cutting board, you can hold the chives directly above the bowl and use the shears to snip them directly into the bowl: faster, and fewer dishes, too!

  Tongs. Think of tongs as heatproof extensions of your fingers. They’re useful not just for flipping French toast in a frying pan or chicken on the grill, but also for picking up ramekins in the oven or grabbing a cookie tray when you’re out of towels. Look for spring-loaded tongs that have silicone or heatproof tips, because these can be used with nonstick coated pans. Scalloped edges are also useful, because they tend to grip things better than their straight counterparts.

  In addition to flipping items in pans or grabbing hot ramekins from an oven, tongs can be useful for holding on to hot foods such as just-cooked sausage while slicing them.

  Thermometers and timers

  Probe thermometers are awesome because they use a thermocouple attached to a long heat-safe lead, designed so that you can stick the probe into a piece of meat and set the controller to beep when it reaches the desired temperature. Timers are handy, and if you’ll be doing much baking, one will be critical. But if you expect to be doing mostly cooking, a timer is just a proxy for checking when, say, an oven roast has reached temperature, in which case why not use something that actually checks that? And when it comes to food safety, it’s not possible to "see" what a hamburger cooked to 160°F / 71°C looks like, even when cut in half.

  Infrared thermometers are great for taking dry temperatures, such as the surface temperature of a frying pan before you start making pancakes, or ice cream you’ve just made with liquid nitrogen (see Making ice cream in Chapter 7). The other great thing about them is that they’re instant: point, click, done. You can also use them to take the temperature of liquids in a pan without having to worry about handling a hot thermometer probe or washing it after. Keep in mind, though, that stainless steel is reflective in the IR range, just like a mirror reflects visible light—you’ll end up taking the temperature of your ceiling, not the pan, if you try to meter an empty stainless steel pan. Also, IR thermometers only take surface temperature, so they shouldn’t be used for checking internal temperatures for food safety.

  Tuck a probe thermometer into a quiche or pie to tell when the internal temperature indicates it is done. I pull my quiches out when the temperature reaches 140°F / 60°C. The egg coagulates in the range of 140–149°F / 60–65°C, and 140°F / 60°C is hot enough that the "carryover" heat will just set the egg custard without making it dry.

  Finally, I’d be remiss if I didn’t mention the most overlooked but useful thermometer: your hands. Learn what various temperatures feel like: hold your hand above a hot pan, and notice how far away you can be and still "feel" the heat (thermal radiation). Stick your hand in an oven set to medium heat, remember that feeling, then compare it when you’re working with a hot oven. For liquids, you can generally put your hand in water at around 130°F / 55°C for a second or two, but at 140°F / 60°C it’ll pretty much be a reflexive "ouch!" Just remember to use a thermometer for foods that need to be cooked to a certain temperature for food safety reasons, which we’ll cover in Chapter 4.

  Mixing bowls

  While you can get away with using your dinner plates or soup bowls for holding some things, you’ll invariably need mixing bowls for working with and storing your ingredients. I recommend two types: large metal bowls (~12 to 16″ / 30 to 40 cm diameter) and small glass bowls.

  For metal bowls, poke around your nearest restaurant supply store for so
me cheap stainless steel ones, which should cost only a few dollars apiece. These bowls are large enough to hold cookie dough, cake batter, and soup, and they have enough room for chopped leafy greens that you plan to sauté. You can also toss them in the oven at low heat to keep cooked items warm, something you can’t do with plastic ones.

  Small glass bowls are also very useful, especially if you’re using a mise en place setup. Measuring out chopped ingredients into small glass bowls ahead of time will allow you to toss the ingredients together much faster during the cooking process. If you have leftovers, just wrap the bowls with plastic wrap and store in the fridge. Look for glass bowls that are all the same size and that stack well. You’ll often find these bowls available at your local hardware store.

  Bar towels

  In addition to wiping off counters with them, you can use bar towels (typically 12″ × 18″ / 30 × 40 cm terry towels with some thickness) as potholders, under a cutting board to prevent slippage, or as a liner in a bowl to help dry washed items such as blueberries or cherries. And you can never have enough of them. I keep several dozen on hand in my kitchen.

  You can use a bar towel as a potholder to handle dishes or pans that have been in the oven. Fold it in half to double the thickness, and don’t use a wet towel because it’ll steam up and burn you. Some people prefer oven mitts, because oven mitts are typically thicker and don’t have the potential to catch on corners like a towel might.