Cooking for Geeks: Real Science, Great Hacks, and Good Food (52 page)
Read Cooking for Geeks: Real Science, Great Hacks, and Good Food Online
Authors: Jeff Potter
Tags: #COOKING / Methods / General
PHOTO OF DAVID BY KRISTIN HOHENADEL / APARTMENT THERAPY: THE KITCHN
[
4
]
Technically, a suboptimal pie-cutting protocol
MANKIND HAS BEEN ADDING CHEMICALS TO FOOD FOR MILLENNIA.
Salt is used both as a preservative (curing meats, inhibiting bacterial growth) and as a flavor enhancer (masking bitterness). Acetic acid, a key component in vinegar and a byproduct of some strains of bacteria, turns cucumbers into pickles and cabbage into the Korean dish
kimchi
. And citric acid in lemon juice brightens the smell and taste of fish by neutralizing the amine compounds that can create that “fishy” smell as the tissue breaks down.
In recent history, the food industry — the collection of businesses that farm, distribute, prepare, and package the foods we eat — has developed a number of techniques to help perishable foods last longer. Refrigeration slows down bacterial growth, “modified atmosphere packaging” (MAP) displaces oxygen to reduce oxidation and retard the growth of aerobic bacteria, and chemical food additives extend shelf life, fortify foods, and aid in mass production. These same chemicals are also used to create entirely new types of foods, including many candies, and as key ingredients in some techniques of an entirely new kind of cooking given names such as
molecular gastronomy
or
modernist cuisine
.
By definition, food itself is made up of chemicals, of course. Corn, chicken, and bars of chocolate are just big piles of well-structured chemicals. For our purposes, we’ll consider a food additive to be any chemical — a compound with a definable molecular structure — used in food that by itself cannot be harvested directly from nature without further refinement or processing.
In this chapter, we’ll take a look at cooking techniques that use food additives, both traditional and modern. Some recent culinary techniques rely on chemical stabilizers, gelling agents, and emulsifiers to create new types of dishes. We’ll cover these chemical-based techniques in the second portion of this chapter. Even if you’re not the type who wants to use chemicals to make foams,
to “spherize” liquids, or to turn liquids into gels, understanding how food additives work and what they do makes recovering from kitchen errors quicker and decoding ingredient lists easier.
One of the largest challenges facing commercial food preparers is extending shelf life while maintaining the taste, texture, and appearance of foods. To reduce costs, speed up manufacturing, and increase the shelf life of products like vegetables and baked cookies from days to months, industry relies on chemicals.
Take a look at the food additives used in a certain popular cream-filled chocolate cookie:
Speeds up manufacturing by immediately giving rise to a dough or batter (via chemically reacting to release carbon dioxide) so you don’t have to wait for the rising action of yeast.
A thickener, also used as a stabilizer. (Cornstarch is derived from corn but is sufficiently processed, filtered, centrifuged, dried, and treated with acids that it should be considered a food additive.)
Fortified with micronutrients that are removed during the processing of white flour. The FDA requires that white flour be supplemented with B vitamins (to prevent various deficiencies) and iron (to prevent anemia, a low red blood cell count).
Used to mask bitterness, to improve flavor, and in some cases to act as a preservative.
An emulsifier, used to prevent oils and water from separating. If you were following a recipe for a cream filling, it would likely call for egg yolks, which are around 10% lecithin, as an emulsifier.
Used as a flavoring agent, vanillin is the primary component of natural vanilla extract and is responsible for the majority of vanilla’s flavor. Vanillin has the molecular formula C
8
H
8
O
3
, regardless of whether the source from which it is derived is “natural” or “artificial.”
Some of these items — baking soda, cornstarch, and salt — might not strike you as food additives, either because of their “natural” origins or their long history in the kitchen. But even baking soda arrived only relatively recently on the food scene, when in 1846 John Dwight and Austin Church figured out a commercial method for manufacturing it.
Food additives are used for the following purposes:
- To preserve nutritional value (preventing the breakdown of food)
- To address dietary needs (via fortification, such as the addition of iodide in table salt)
- To extend shelf life or stability in order to keep the food enjoyable longer (e.g., treating apricots with sulfur dioxide to preserve color)
- To aid in manufacturing, processing, or transportation — that is, to address issues caused by scaling to mass production (i.e., keeping larger volumes of food consistent)
Most commercially prepared food products use food additives for more than one of these purposes. In the cookie example just cited, baking soda speeds up manufacturing, cornstarch and soy lecithin aid in the manufacturing process, salt and vanillin improve flavor for enjoyment, and flour is fortified to address dietary needs.
Food additives have gotten something of a bad rap in recent years. The politics, economics, and trade-offs of a food supply that is necessarily driven by economics are well beyond the scope of this book. For now, keep in mind that food itself is chemical, and to cook is to cause chemical and physical reactions.
Just as there have been food additives that were once thought safe but turned out to be dangerous (e.g., red dye no. 2), there are “natural” items — foods from the earth — that pose their own risks without human processing (e.g., hydrocyanic acid in raw lima beans, which is neutralized by cooking). The source of a chemical — natural versus man-made — should not be your sole distinguisher of safety. No one would argue that hemlock or botulinum toxins — both “all natural” — are things you should be adding to your midnight snack.
Taste tests done by America’s Test Kitchen have found that most pastry chefs are unable to discern the difference between natural and artificial vanilla, much to the chefs’ embarrassment.
Before getting into modern industrial chemicals — chemicals that began to routinely appear in food only after World War II — let’s take a look at some traditional food additives and the chemicals and chemistry behind them: salt (sodium chloride), sugar (sucrose), acids and bases (citric acid, lye), and alcohol (ethanol).
Ahh, salt: responsible for the salvation of many a food (or is that salivation?). The oldest seasoning in use, in small quantities it helps reduce the bitterness of foods and enhances the other flavors in a dish (for a discussion of the gustatory system, see
Taste (Gustatory Sense)
in
Chapter 3
). In larger quantities, it can be used chemically to preserve food (dry and wet brining) as well as mechanically to alter how foods cook (salt roasting).
IMAGE COURTESY OF NASA
Salt crystals.
From a chemistry perspective, salt is an ionic compound composed of a cation from a metal or ammonium and an anion from an acid. In solid form, salt is a crystal of atoms arranged in an alternating pattern based on charge: cation, anion, cation, anion, arranged in a 3D checkerboard pattern.
Our tongues detect one kind of salt, sodium chloride, as being “salty.” Sodium chloride (common table salt) is made up of sodium (a metal, and one that in its pure form happens to react violently when dropped in water) and chloride (chlorine with an extra electron, making it an anion). Other salts can register as different tastes. Monosodium glutamate, for example, triggers our taste receptors for umami. In water, the salts dissolve and the individual ions are freed, and they are then able to react and form bonds with other atoms and molecules.
While at first glance the chemistry of salt may not seem important to everyday cooking, it’s helpful to understand the basics of how it works when preparing and cooking food. Here’s a quick refresher on a few chemistry definitions that’ll pop up throughout this chapter. (Finally, a use for that high school chemistry!)
Basic building block of matter; these are the elements listed in the periodic table.
Two or more atoms bonded together (where “or more” can be millions). H = hydrogen atom, H
2
= dihydrogen molecule.
Any positively charged atom or molecule (i.e., one that has more protons than electrons).
Any negatively charged atom or molecule (i.e., one that has more electrons than protons).
Cations and anions can be a single atom (Ca
2+
) or anything from a small molecule (NO
3
) to a really large one, such as alginate (composed of many thousands of atoms).
Applying salt to the outside of fish causes osmosis, which is the physical process of a solvent passing through a membrane to equalize the concentration of solute on the membrane’s other side.
In animal tissue, salt (the solute) is unable to penetrate the cell walls (the membrane) present in the tissue, so water (the solvent) leaves the cells in order to equalize the differences in concentration. (The process of equalizing osmotic pressure is called
diffusion
.) If there’s a large enough difference in solute concentrations, at some point plasmolysis occurs — the cell structure collapses — and if enough water leaves the cell, the cell dies.
From a food safety perspective, the amount of salt necessary to cause sufficient plasmolysis to render bacteria nonviable depends on the species of bacteria involved. Salmonella is unable to grow in salt concentrations as low as 3% and
Clostridium botulinum
dies at around 5.5%, while
Staphylococcus
is hardy enough to survive in a salt concentration up to 20%.
Staphylococcus
is not a common concern in fish, according to the FDA, so food safety guidelines consider salt solutions of ~6% sufficiently safe (except for those in an at-risk group) when curing fish.
Beef jerky, salmon gravlax, sausages, hams, prosciutto, and corned beef are all cured using salts, typically sodium chloride (table salt) or sodium nitrate, which gives foods like salami a distinctive flavor and pinkish color. Besides adding flavor, salt preserves these types of foods by creating an inhospitable environment for microorganisms (see the section
Foodborne Illness and Staying Safe
in
Chapter 4
).
Salt curing has been used for centuries to preserve fish caught at sea, and it’s also something that you can easily do at home. Surrounding it with a sufficient quantity of salt draws moisture out of food; this is called dry brining. But salt doesn’t just “dry out” the food (along with any bacteria and parasites). At sufficient concentration, it actively disrupts a cell’s ability to function and kills it, rendering bacteria and parasites nonviable.
This killing ability isn’t limited to just foods. For an adult human, the lethal dose of table salt is about 80 grams — about the amount in the saltshaker on your typical restaurant table.
Overdosing on salt is reportedly a really painful way to go, as your brain swells up and ruptures. Plus, it’s unlikely the ER physicians will correctly diagnose the cause in time. (Paging Dr. House.)
Wet brining — the process of soaking meat in salted water — can be used both to add flavor and to reduce water loss during cooking.
As an experiment, try doing an A/B test with brined and nonbrined pork chops. Does brining change the weight loss during cooking? Using a gram scale, weigh a pork chop pre-brining, post-brining, and after cooking, and compare the percentage weight loss to that of a “control” pork chop that is cooked without having been brined. You may also want to test how brining changes the flavor. If you’re cooking for others, enlist them as tasters. Cook both brined and nonbrined pork chops, serve a portion of each to everyone, and see what preferences your tasters have.
In a bowl, mix together:
- 5 teaspoons (30g) kosher salt
- 1 tablespoon (12g) sugar
- 3 tablespoons (12g) finely chopped fresh dill
- 1 teaspoon (4g) vodka
- 1 teaspoon (2g) crushed peppercorns (ideally, use a mortar and pestle)
On a large piece of plastic wrap, place:
- 1 pound (450g) salmon, washed and bones removed; preferably a center cut so that its shape is rectangular
Sprinkle salt mixture over fish and massage into salmon. Wrap fish in plastic and store in fridge, flipping and massaging twice a day for a day or two.
Store in the fridge and consume within a week.
Notes
- Note the use of vodka as a solvent. Try substituting other spirits, such as cognac or whiskey. And in place of dill, try using coriander seed, loose tea leaves (e.g., Earl Grey or Lapsang Souchong), shallots, or lemon zest. The Scandinavians traditionally serve salmon gravlax on top of bread with a mustard dill sauce.
- You can substitute other fatty fish for the salmon and obtain a similar texture. What happens if you try tuna?
- Curing inhibits most common bacterial growth but does not prevent all types of bacteria from growing. Avoid serving this to anyone in an at-risk group. This recipe is a bit heavy on the salt — 6% by weight — to err on the side of safety. You can reduce the saltiness by rinsing the finished product in fresh water, followed by recoating it with dill and ground pepper to restore some of the flavor. For food safety issues related to parasites, see the section
How to Prevent Foodborne Illness Caused by Parasites
in
Chapter 4
.NoteFor an extremely technical guide to curing fish and potential pathological hazards, see
http://www.fda.gov/Food/ScienceResearch/ResearchAreas/SafePracticesforFoodProcesses/ucm094579.htm
; for a more practical guide, see
http://www.cfast.vt.edu/downloads/fstnotes/salting.pdf
. - Salt curing — as is done in salmon gravlax — is the first step in making lox. After curing, lox is also cold smoked, which is the process of exposing a food to smoke vapors that have been cooled down. You can approximate the flavor of lox by adding liquid smoke to the rub (see
Liquid Smoke: Distilled Smoke Vapor
).
You can remove the skin from a piece of fish by placing it skin-side down on a cutting board and carefully running a knife along the surface between the skin and flesh while using your hand to keep the fish from sliding around.
Brined pork chops are a good example of wet brining. This is also one of those dishes that’s both tasty and easy.
In a container, mix 2 tablespoons (60g) salt with 4 cups (1 liter) of cold water. Stir to dissolve salt. Place 2 to 4 boneless pork chops in the brine and store them in the fridge for an hour. After pork chops have brined, remove from water and pat dry with paper towels. Lay out the pork chops on a clean plate to allow them to come to room temperature.
Create a filling by mixing together in a bowl:
- ¼ cup (40g) poblano pepper, roasted and
then
diced, about 1 pepper (see notes) - ¼ cup (40g) cheddar cheese or Monterey Jack cheese, cut into small cubes
- ½ teaspoon (3g) salt
- ½ teaspoon (1g) ground black pepper
Prepare the pork chops for stuffing: using a small paring knife, make a small incision in the side of the pork chop, then push the blade into the center of the pork chop. Create a center cavity, sweeping the blade inside the pork chop, while keeping the “mouth” of the cavity — where you pushed the knife into the meat — as small as possible.
Stuff about a tablespoon of the filling into each pork chop. Rub the outside of the pork chops with oil and season with a pinch of salt.
You’ll have leftover filling. It’s better to make too much than risk not having enough. Save the extra stuffing for scrambled eggs.
Heat a cast iron pan over medium heat until it is hot (about 400°F / 200°C, the point at which water dropped on the surface sizzles and steams). Place the pork chops in the pan, searing each side until the outside is medium brown, about five to seven minutes per side. Check the internal temperature, cooking until your thermometer registers 145°F / 62.8°C. Then remove the pork chops from the pan and let them rest on a cutting board for five minutes.
You can pull the pork chops from the pan before they reach temperature and let the carryover bring them up to 145°F / 62.8°C, but make sure they do get up to this temperature. You should also verify that your thermometer is calibrated correctly and that you properly probe the coldest part of the meat.
To serve, slice the pork chops in half to reveal the center. Serve on top of rosemary mashed potatoes (see
Rosemary Mashed Potatoes
in
Chapter 4
).
Notes
- How do you roast a poblano pepper? If you have a gas stovetop, you can place the pepper directly on top of the burner, using a pair of tongs to rotate it as the skin burns off (expect the skin to char and turn black; this is what you’re going for). If you don’t have a gas stovetop, place the pepper under a broiler (gas or electric) set to high, rotating it as necessary. Once the skin is burnt on most sides of the pepper, remove from the heat and let it rest on a cutting board until it’s cool enough to handle. Using a cloth or paper towel, wipe off the burnt skin and discard. Dice the pepper (discarding the seeds, ribbing, and top) and place into a bowl.
- Try other fillings, such as a mixture of sage, dried fruits (cranberries, cherries, apricots), and nuts (pecans, walnuts); or pesto sauce.
145°F / 62.8°C? I thought pork had to be cooked to 165°F / 73.9°C!
Good question; glad you asked. Trichinosis — a parasitic infection from roundworm — has historically been a concern in pork, but this is no longer the case in the United States. The U.S. Code of Federal Regulations requires commercial processors that cook pork to heat it to 140°F / 60°C — well below the well-done temperature of 165°F / 73.9°C — and hold it at that temperature for at least one minute.
To be safe (well, safer — see the discussion on food safety in
Chapter 4
), give yourself at least a 5°F / 2°C error window. When cooking pork chops, leave the temperature probe in after the chop reaches temperature and check that the temperature
remains at or above
145°F / 62.8°C for at least one minute. If you see the temperature drop down, transfer the chops back to the pan. The pan itself — even off-heat — should have enough residual heat to keep them at 145°F / 62.8°C.
If you’re curious about the history of trichinosis, see the USDA’s Parasite Biology and Epidemiology Lab fact sheet at
http://www.aphis.usda.gov/vs/trichinae/docs/fact_sheet.htm
. A century ago, ~1.4% of pork was infected; in 1996, of 221,123 tested animals in the United States, 0 were infected.
Salt can also be used as a “protective outer layer” on food during cooking. By packing foods such as fish, meats, or potatoes in a mound of salt, you ensure that the outer surface of the cooked food doesn’t reach the same surface temperatures as it would if uncovered, leading to a less extreme gradient of doneness (see
Temperature gradients
in
Chapter 4
).
Traditionally, the salt is mixed with egg white or water to make a thick paste that will hold its shape and can be packed around something like a fish.
When salt roasting, leave the fish skin on. It’ll prevent the fish from getting too salty.
You don’t need to bury the fish too deeply. Go for about ½” / 1 cm of salt on all sides — enough to take the brunt of the surface temperature but not so much that the center of the fish takes too long to actually reach temperature.
Try this with a whole fish, something medium to large (2 to 5 lbs / 1 to 2 kilos), such as a striped bass or rockfish (check
http://seafoodwatch.com
for suggestions). Rinse the fish thoroughly, and add some herbs (rosemary, bay leaf, etc.) and lemon wedges in the center. Line a baking pan with parchment paper (this’ll make cleanup easier), and add a thin layer of salt. Place the fish on top of the salt, and then pack the rest of the salt around the sides and top of the fish.
Bake the fish in an oven set to 400–450°F / 200–230°C, using a probe thermometer set to beep when the internal temperature reaches 125°F / 52°C. Remove from oven and let rest 5 to 10 minutes (during which carryover will bring the temp up to 130°F / 54°C). Crack open the layer of salt and serve.
Notes
- Don’t have a probe thermometer? The Canadian Department of Marine Fisheries recommends measuring the thickest part of the fish and cooking for 10 minutes per inch. (Add ~10 minutes for the 1” / 2.5 cm of salt around the fish.)
- Try this with other foods, such as pork loin (add spices — black pepper, cinnamon, cayenne pepper — to the salt mixture) or even entire standing rib roasts.
- Sugar can also work as a “packing material,” provided that the oven temperature remains sufficiently low. Salt melts at 1474°F / 801°C, well above oven temperature; sugar melts at 367°F / 186°C. Given this, you should be able to do the equivalent of salt roasting with sugar at temperatures below 367°F / 186°C (try around 325°F / 163°C). However, it takes less water to dissolve the same amount of sugar, so moist items such as fruits will end up giving off too much water for this to work. When I tried “sugar roasting” an apple at 340°F / 170°C, the moisture in the apple was enough to allow the sugar to dissolve into a syrup. It was still delicious, though.
100 grams of salt (left) and 100 grams of sugar (right), each with 30 grams of water.