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

by Jeff Potter

  Meats. Follow the sell-by or use-by date. The sell-by date is the point in time until which the store still considers the product safe for sale. (Not that you should push it, but it’s not as if the meat will suddenly turn green and smelly at 12:01 a.m. the next day.) The use-by date, as you’d imagine, is the recommended deadline to cook the food. If you have a package of chicken whose use-by date is today, cook it today, even if you’re not ready to eat it. You can store the cooked product for a few more days. If you can’t cook the fish or meat you’ve bought on or before its use-by date, toss it in the freezer. This will affect the texture, but at least the food won’t go to waste.

  Freezing meat does not kill bacteria. It takes being zapped with radiation AND over a month at 0°F / –18°C to render nonviable the bacteria in salmonella-contaminated meats. Nice to know, but not very helpful unless you happen to have a radiation chamber lying around.

  Fruits and vegetables. How you process and store fruits and vegetables impacts their ripeness and flavor, and can also delay the growth of mold. When it comes to ripening, there are two types of fruit: those that generate ethylene gas, which causes them to ripen, and those that don’t generate it. For those that do ripen when exposed to ethylene, you can speed up ripening by storing them in a paper bag, which traps the gas.

  Store raw meats below fruits and vegetables in your refrigerator, because this reduces the likelihood of cross-contamination. Any liquid runoff from the meats won’t be able to drip onto other foods that won’t be effectively pasteurized by cooking. (Storing meats below other foods is required by health code in commercial establishments.)

  Ripen in the presence of ethylene gas To speed up ripening, store these in a loosely folded paper bag out of direct sunlight, at room temperature.

  Unaffected or negatively impacted by ethylene gas Store these separately from ethylene-producing produce.

  Apricots, peaches, plums. Ripe fruits will be aromatic and will yield slightly to a gentle squeeze, at which point you can store them in the fridge. Don’t store unripe stone fruits in the refrigerator, in plastic bags, or in direct sunlight. If you’re lucky enough to be gifted pounds and pounds of these fruits, either freeze them or make jam before they have a chance to go bad.

  Avocados. Ripe fruit will be slightly firm but will yield to gentle pressure. Color alone will not tell you if the avocado is ripe. Storing cut avocados with the pit doesn’t prevent browning, which is due to both oxidation and an enzymatic reaction, but does stop browning where the pit prevents air from coming in contact with the flesh. Plastic wrap pressed down against the flesh works just as well, or if you have a vacuum sealer, go for overkill and seal them.

  Bananas. Leave at room temperature until ripe. To prevent further ripening, store in the refrigerator—the peel will turn brown, but the fruit will not change.

  Blueberries. While blueberries do ripen in the presence of ethylene, their flavor is not improved from this. See advice for blackberries et al.

  Tomatoes. Store at temperatures above 55°F / 13°C. Storing in the fridge is okay for longer periods of time but will affect flavor and texture. If the ultimate destination for the tomatoes is a sauce, you can also cook them and then refrigerate or freeze the sauce.

  Potatoes. Keep potatoes in a cool, dry place (but not the fridge). Sunlight can make the skin turn green. If this occurs, you must peel off the skin before eating. The green color is due to the presence of chlorophyll, which develops at the same time that the neurotoxins solanine and chaconine are produced.[a] Since most of the nutrients in a potato are contained directly below the skin, avoid peeling them whenever possible.

  Asparagus. Store stalks, with bottoms wrapped in a damp paper towel, in the crisper section or the coldest part of the fridge. You can also put them in a glass or mug, like cut flowers. Eat as soon as possible because the flavor diminishes with time.

  Blackberries, raspberries, and strawberries. Toss out any moldy or deformed berries. Immediately eat any overripe berries. Return the other berries to the original container, or arrange them (unwashed) in a shallow pan lined with paper towels and store in the fridge. To absorb additional moisture, place a paper towel on top of the berries. Wash them just prior to use; washing and storing them adds moisture that aids the growth of mold.

  Broccoli, cabbage, collard greens, kale, leeks, Swiss chard. Store in the crisper drawer of the refrigerator or in a plastic bag poked with holes to allow for any excess moisture and ethylene to escape. Ethylene causes florets and leaves to turn yellow.

  Carrots. Break off green tops. Rinse carrots, place in a plastic bag, and store in the crisper section of the fridge. Storing carrots in the fridge will preserve their flavor, texture, and beta-carotene content.

  Garlic. Store in a cool, dark place (but not the fridge). You can still use cloves that have sprouted, but they will not be as strong in flavor. The sprouts themselves can be cut up like scallions or chives and used in dishes.

  Lettuce and salad greens. Check greens bought in bunches for insects. Wash leaves, wrap in a towel or paper towel, and then store in the fridge in a plastic bag.

  Onions. Keep in a cool, dry space away from bright light. Onions do best in an area that allows for air circulation. Do not place onions near potatoes, because potatoes give off both moisture and ethylene, causing onions to spoil more quickly.

  Questions about other produce?

  See http://www.fruitsandveggiesmatter.gov and http://postharvest.ucdavis.edu/Produce/ProduceFacts/.

  [a] While you’re unlikely to die from consuming the solanine content present in an average potato that’s gone green (~0.4 mg), it appears to be possible to give yourself a rather unpleasant digestive tract experience for the better part of a day. For a more thorough explanation, see http://en.wikipedia.org/wiki/Solanine.

  Here’s what I consider the essential kitchen items. We’ll cover each in turn.

  Bare Minimum Equipment

  Standard Kitchen Equipment

  Knives

  Cutting board

  Pots and pans

  Measuring cups and scales

  Spoons & co.

  Thermometer and timers

  Bar towels

  ← All that, plus...

  Storage containers

  Strainers

  Mixers & co.

  Bare Minimum Equipment

  Here’s the equipment that you’ll need at a bare minimum.

  Knives

  Knife blades made of steel are manufactured in one of two ways: forging or stamping. Forged blades tend to be heavier and "drag" through cuts better due to the additional material present in the blade. Stamped blades are lighter and, because of the harder alloys used, hold an edge longer. Which type of knife is better is highly subjective and prone to starting flame wars (or is that flambé wars?), and with some specialty sashimi knives listing for upward of $1,000, there are plenty of options and rationales to go around.

  Some people like a lighter knife, while others prefer something with more heft. Personally, I’m perfectly happy with a stamped knife (currently, Dexter-Russell’s V-Lo series) for most day-to-day work, although I do have a nice forged knife that I use for slicing cooked meats.

  Chef’s knife. If I could take only one tool to a desert island, it would be my chef’s knife. What size and style of chef’s knife is best for you is a matter of preference. A typical chef’s knife is around 8″ / 20 cm to 9″ / 23 cm long and has a slightly curved blade, which allows for rocking the blade for chopping and pulling the blade through foods. If you have a large work surface, try a 10″ / 25 cm or larger knife. Or, if you have smaller hands, you might want to look at a Santoku-style knife, a Japanese-inspired design that has an almost flat blade and a thinner cross-section. Keep in mind, though, that Santoku knives are best suited for straight up-and-down cutting motions, not rocking chopping motions or pulling through foods.

  Paring knife. A paring knife has a small (~4″ / 10 cm) blade and is probably the most versatile knife in the kitchen.
I’ve had some chefs confide to me that their favorite knives are the scalloped paring knives, since they are useful for cutting so many different types of items. They’re designed to be held up off the cutting board, knife in one hand, food item in the other, for tasks such as removing the core from an apple quarter or cutting out bad spots on a potato. I find that the almost pencil-like grip design of some commercial paring knives allows me to twirl and spin the knife in my fingers, so I can cut around something by rotating the knife instead of rotating the food item or twisting my arms. Personally, I prefer a scalloped blade—one that is serrated—because I find it cuts more easily.

  Bread knife. Look for an offset bread knife, which has the handle raised up higher than the blade, avoiding the awkward moment of knuckles-touching-breadboard at the end of a slice. While not an everyday knife, in addition to cutting bread and slicing bagels, bread knives are also handy for cutting items like oranges, grapefruits, melons, and tomatoes because of the serrated blade.

  Boning knife. If you plan to cook fish and meat, consider acquiring a boning knife, which is designed to sweep around bones. A boning knife has a thinner, more flexible blade than a chef’s knife, allowing you to avoid hitting bones, which would otherwise nick and damage the knife blade. Some chefs find them indispensable, while others rarely use them.

  Knife Skills 101

  The sound of a failed disk drive grinding itself down is pretty bad, but watching someone use a knife improperly is far worse. I swear, if I were going to develop PTKD (post-traumatic kitchen disorder) over something, it’d be from watching people use knives improperly.

  I treat knives as the second most dangerous implements in the average kitchen. (Microplanes and mandolins hold the top spot.) When using a knife, I’m always thinking about the "failure mode." If it slips, or something goes wrong, how is it going to go wrong? Where is the knife going to go if it does slip? How can I use the knife and position myself such that if an exception does occur, it isn’t fatal? Of course, getting a good, clean cut and keeping the knife in good working order are also important. Here are my top tips for knife usage:

  Feed the food into the cutting plane with your fingers positioned so that they can’t get cut. Keep the fingers of the hand holding the item curled back, so that if you misjudge where the knife is, or it slips, your fingers are out of harm’s way. You can also rub the upper side of the knife against your knuckles to get better control over the location of the knife. Use a smooth, long motion when cutting. Don’t saw back and forth, and don’t just press straight down (except for soft things like a block of cheese or a banana). Let the knife do the work!

  When scraping food off a cutting board, flip the knife over and use the dull side of the blade. This will keep the sharpened side sharper.

  There’s more than one way to hold a knife: try using a "pinch grip" instead of a "club grip." A pinch grip allows for more flexibility, as it gives you more dexterity in moving the knife.

  Don’t use the edge of the blade to whack or crack hard objects, such as a walnut shell or a coconut; you’ll nick it! Repeat after me: knives are not hammers (you know who you are). Unless, of course, you have a commercial knife that has a butt that actually is a hammer, in which case, go right ahead... You can, however, use the side of the blade as a quick way to crush garlic or pit cherries or olives. Place food on board, place side of blade on top of food, press down on blade with fist.

  Buck Raper on Knives

  PHOTOS USED BY PERMISSION OF BUCK RAPER

  Buck Raper is the manager of manufacturing and engineering for Dexter-Russell, the largest and oldest cutlery manufacturer in the United States. Above, Buck holds a knife next to an edge sharpness and edge life test apparatus in their metallurgy lab.

  How did you come to work at Dexter-Russell?

  In a former life, I was working on a doctorate in synthetic organic chemistry.

  Wow. What happened?

  I got drafted to Vietnam.

  And then you came back...

  I came back and there weren’t many job opportunities for PhD chemists, and I was still looking at two more years in school, and I had a family to support. So I went and got an MBA and got twice the starting salary I would have gotten as a PhD. My family had always been in the cutlery business, my grandfather, and my father, and all I ever heard was knife talk. When I was a Baby Buck, my father would take me into the pocket-knife factory on Saturday mornings and hand me off to a foreman so he could get some work done, and I’d make knives with a foreman.

  Did the background in chemistry, combined with your family’s history in knife making, complement each other?

  To some degree...but it was more of the scientific method and analytical techniques that you learn in a hard science, applying them to manufacturing. I looked at it from a different standpoint than a history major MBA would, or an English major MBA would. Coming from a real science, you take a different approach, an engineering approach.

  Can you give me an example?

  Much of the heat treating, the grinding, and the choice of steels was done almost by folklore. It’s always been done that way and nobody remembers why. Now when we’re trying to choose a steel for a particular application, we do some testing, make some blades, and try them out to see what the results are. We have a control sample and record data. That’s the type of change that I made. Dexter-Russell is 192 years old, and we still have machinery and tooling that we were using at the turn of the century, from 1900. Those techniques still work and they’re still very good, but nobody really knew why we were doing things the way we were doing them.

  What surprised you when you were testing the folklore?

  We’re number one in professional oyster knives, and there’s the chronic problem with the tips of oyster knives breaking off. We had a heat-treatment process that we thought was making the steel hard enough to not break. The theory was if the blade is breaking, make it harder, and then the tip won’t break off. The reality was what we needed to do was to make tougher steel. So we changed our heat treatment process to create a tougher, softer steel.

  What does it means for a steel to be tough versus hard?

  It’s a trade-off to hold an edge. The harder the steel is, the better it will hold an edge. But you also want to have some flexibility. If you need a flexible bone or fillet knife, a harder steel is more brittle; it would fracture. So you have to trade off the hardness for the toughness that allows you some flexibility. The toughness also gives you wearability, resistance to abrasion. One way an edge fails is that you literally wear away the grains of steel, and to resist that, you’re looking for a tough steel.

  When you heat-treat steel, you martenize it to the temperature that’s going to give you the maximum hardness. But if you underheat it, if you undercook it a little bit, it comes out tougher. If you overcook it, it’s also tough, but then it corrodes. In our case, when we’re talking heat-treatable stainless 400 series steel, the optimum temperature is 1934°F / 1057°C. If you heat it to 1950°F / 1066°C, you get the same hardness that you would if you heat it to 1920°F / 1049°C, but one is tougher, and the other will corrode.

  Steel is formed of grains. If you were to snap a knife blade in half, and look at it with the naked eye, the texture would look like a fine cement inside the knife. What you’re seeing is groups of grains. Steel exists in 9 or 10 different phases. Depending on how it’s been processed, temperature-wise, it has a mixture of these various phases, and that determines the toughness of the steel. I use the analogy of baking a cake when I’m explaining heat treatment. You have raw dough and expose it to heat. There’s a chemical change and a phase change, and you go from slurry to a porous solid once it’s baked.

  With steel, once it is heated to a critical temperature, cooling—called quenching—is also critical. You’ve probably seen old movies where the blacksmith is pounding away, when he gets the iron hot, he plunges it into the water and there’s a hiss of steam. The reason for that is the rapid cooling. In the case of st
ainless steel, you have to get it below 1350°F / 732°C in less than three minutes in order to maintain the phase that you want. If you cool it slower, you get a different mixture of phases in the steel. So it’s not just in bringing it up to temperature, the cooling curve is key.

  Steel is also determined by the alloy. There’re two or three dozen different types of stainless cutlery steels, and stainless cutlery steels are just a very small subset of alloyed steels. Alloyed steels are a subset of carbon steels. And all the heat-treatment processes are determined by which alloy you’re working with.

  Are there other types of steels that you would want to use for particular purposes for knife making?

  We want to use a stainless steel, although carbon steel makes wonderful knives. Everybody likes their old carbon steel knives, but nowadays, with the National Sanitation Foundation and other regulatory bodies, you can’t use carbon steel knives in most restaurants. We choose stainless, which has chromium in it; the chromium makes it stainless. You also have to have carbon in the steel so that you can harden it. You add more carbon if you want to create a harder blade, and more chromium if you need to get more corrosion resistance. When you heat-treat it, you want to come out with a very fine texture, and things like molybdenum, vanadium, tungsten, and cobalt help you get a fine grain. Tungsten and cobalt help make the steel tougher.