Harold McGee Speaks

Harold McGee is the king of kitchen science, the man who solves food mysteries ranging from how much oil you can emulsify into a mayonnaise with one egg yolk (answer: gallons) to why frying spatter ends up on the inside surface of the cook’s eyeglasses (gravity).

Pressed garlic vs. chopped: Is there a difference?

The strong aroma and pungency of raw garlic is created when the garlic tissue is cut or crushed. The physical damage releases enzymes that act on certain sulfur-containing chemicals and transform them into a host of flavorful molecules, which then go on to react with each other and with other molecules in the vicinity, especially oxygen. The exact mix of molecules, and so the overall flavor, depends on how the garlic is handled. Crushing breaks many cells at once; chopping with a knife breaks fewer cells and develops less flavor. A food processor slices through the tissue thousands of times, exposes more cells to the air, and often produces the harshest results.

Are charred bits of barbecue really carcinogenic? They’re the best part.

The same high cooking temperatures that give meats and fish a tasty brown crust also turn out to generate chemicals called HCAs (heterocyclic amines) that damage DNA and cause cancer in lab animals. The higher the temperature and the more intensely flavored and colored the meat surface, the more HCAs. It’s probably a good idea to eat grilled meats and fish only occasionally and to avoid the thoroughly charred bits. HCA production can be greatly reduced by preflavoring the food in a thin, acidic marinade—made from wine, vinegar, or citrus juices—for an hour or so. The added moisture slows the charring, and the acidity inhibits some of the reactions.

Will bamboo cutting boards dull your knives?

Bamboo wood is about as hard as oak and somewhat harder than maple. Any surface will eventually dull a knife edge, but the difference in hardness between bamboo and maple is probably less significant than the frequency with which cooks steel or sharpen their blades.

Heating food in plastic in the microwave: Is it safe?

Plastic food wraps are built mainly from very long, inert molecules, but they owe much of their flexibility to “plasticizers,” small molecules that lubricate the long ones and that can migrate from wraps into foods they’re in direct contact with. Some plasticizers are suspected of interfering with hormone systems in animal bodies, so it’s prudent to avoid this contamination as much as possible. Plasticizers are especially likely to move into high-fat foods and hot foods. When heating foods in the microwave, try to keep the plastic wrap from direct contact with the food, or use a glass or ceramic container.

Most recipes tell you to salt the water when cooking pasta. Why?

Cooks give several reasons for boiling pasta in salted water. Some say salt raises the boiling point and cooks the pasta faster; some say it toughens the pasta and makes it less vulnerable to overcooking; and some say it just makes the pasta tastier. In fact, normal amounts of salt do not raise the cooking temperature significantly. And while salt does toughen wheat gluten and slow the softening of starch granules, these effects don’t make a noticeable difference. It really does come down to taste. Pasta cooked in unsalted water tastes bland, and that internal blandness can be noticeable even when the pasta is salted afterward or dressed in a sauce.

How about veggies?

Salting the water for cooking green vegetables matters more. The cells of these tender leaves and pods are full of tasty salts and sugars and acids, all dissolved in the cell fluids. If the vegetables are cooked in plain water, then the vegetables’ dissolved substances will move out into the cooking water to even out the osmotic imbalance. Adding salt to the pot balances the levels of dissolved substances in the cells and in the cooking water and reduces the extraction of flavor from the vegetables. Salted water also softens the plant cell walls faster, thus reducing cooking time and destruction of heat-sensitive vitamins.

So when is the right time to salt?

You can add the salt anytime up to a half-minute or so before you add the food; it takes a few seconds to dissolve in hot water. It’s hard to specify quantities by volume; a tablespoon of Morton’s and kosher and sea salt have very different weights, and it’s the weight that matters. For flavoring pasta, about 10 grams of salt per quart is enough; for vegetables, where you’re trying to balance the concentration of dissolved materials in the plant cells, 20 to 30 grams per quart is better.

Harold McGee is the author of the recently revised On Food and Cooking: The Science and Lore of the Kitchen (Scribner).