Marlene Parrish - What Einstein Told His Cook 2

When chemically pure garlic oil is required for nonfood purposes (it is an effective antibacterial, antifungal, and insecticide), it is obtained, as are most plant essential oils, by steam distillation, in which the crushed plant material is boiled in water. The resulting mixture of steam and vaporized oil is condensed, whereupon the water and the oil settle out as separate layers.

All right, then. So is garlic-infused olive or other vegetable oil dangerous? It depends on how you make it. If you add garlic cloves willy-nilly, unpeeled or peeled, whole or minced, to oil and let it stand for weeks at room temperature, yes, you’re flirting with botulism.

The lethal Clostridium botulinum bacterium lives in the soil and in stream and lake sediments, among other places. It cannot flourish in extreme dryness or in air, but will thrive in a moist, airless (anaerobic) environment. And exactly those conditions can exist on the surface of a moist garlic clove smothered in oil.

Many references tell us that C. botulinum bacteria can be killed by being heated for 10 minutes at a temperature above 175°F (79°C) or that they can at least be inhibited by acidic media below pH 4.6. That’s true of the active bacteria themselves, but their dormant spores, if present, can survive long periods of highly unfavorable environments such as air, dryness, and high temperatures. In fact, the 175-degree treatment may only “heat-shock” the spores into germinating more readily. The spores are not reliably killed until subjected to a temperature of 250°F (121°C) for several minutes, as is done in commercial canning. At home, that temperature can be reached in either an oven or a pressure cooker. But simple boiling or simmering will not do the job.

Executing the bacteria and their spores may be too little and too late, however, because it’s not the bacteria themselves that are the potential killers; it’s a neurotoxin they manufacture while multiplying. Botulinum toxin is one of the most powerful poisons known.

Virtually all references repeat the statement that the toxin is not destroyed by the heat of cooking. But that’s a precautionary oversimplification. The toxin is actually unstable to heat, but it depends on what we mean by “cooking.” Research by several groups of scientists in the 1970s showed that different amounts of toxin, different foods, different pH’s, and different acids can affect the toxin-deactivation process differently. So it is indeed prudent to assume that you can’t get rid of it by “cooking.”

The symptoms of botulin poisoning were named botulism when a number of people died in Germany in the late eighteenth century after eating contaminated sausage; the Latin word for sausage is botulus . Botulism is a rare occurrence, with only ten to thirty outbreaks per year in the United States, so there is hardly a galloping botulism plague going on. But a head of garlic just might have some C. botulinum spores lurking under its skin, where they would lie protected from air until they found themselves in an airless medium, such as when submerged in a sea of oil. There, the spores could become active and launch a reproductive orgy, even at refrigerator temperatures. It’s the better part of valor, therefore, not to tempt fate by making your own garlic-infused oil. Commercial garlic-infused oil products are usually acidified with vinegar to thwart bacterial growth. But acidifying a solid in an oil can be tricky, so it isn’t recommended for home preparation of garlic-flavored oil.

Still want to make some? Adventurous types should make only a small amount from chopped garlic in olive oil, keep it refrigerated, and discard what isn’t used after a week or two.

CURB THAT SPERB!

Sometimes a recipe will direct that a spice or herb be added at the beginning of cooking, and sometimes only near the end of a long simmer. Does it really matter? If so, why?

Yes, it matters.

The amount of flavor contributed by a spice or herb depends on the amount of essential oil it contains, not on the total amount or weight of the whole substance. Spices and herbs—instead of repeating “spice or herb” eleven more times in this section, may I call them generically “sperbs”? Thank you—sperbs that are powdered or ground give up their oils readily in the heat of cooking because their huge surface areas allow their essential oils to evaporate quickly. Thus, finely divided sperbs should be added near the end, rather than the beginning of cooking, lest all their essential oils evaporate and the kitchen smell better than the food tastes. Whole sperbs on the other hand, such as peppercorns and bay leaves, give up their essences slowly and are added at the beginning.

Because most essential oils are volatile, sperbs lose their effectiveness in storage as the oils slowly evaporate. So fresh sperbs are always more potent than stale ones. Even low levels of heat can slowly drive off the oils, so sperbs also should be stored in a cool location. Ground sperbs lose their strength by evaporation much faster than whole ones.

Nutmeg and black pepper, especially, should always be bought whole and ground on the spot when needed. Hot chili peppers, on the other hand, keep their heat even when dried and ground, because capsaicin, the “hot stuff” in them, is not very volatile. That’s why you can’t tell how hot a pepper is by smelling it.

You’d be surprised at how much of most sperbs’ verve is lost over the period of a year or less, especially if ground. Sniff your sperbs; if you can recall that they smelled much more potent when new, replace them with fresh samples. It’s a good idea to date the labels when you buy them. And check the vividness of their colors periodically. Green, leafy herbs such as tarragon and rosemary fade with age, as do red spices such as Cayenne pepper, paprika, and chili powder.

Some sperb fanatics (sperbivores?) go so far as to keep their sperbs in the freezer. I don’t see why that shouldn’t work.

THE FOODIE’S FICTIONARY:Fennel—a device for pouring liquids into small containers

HOW MUCH IS THAT HERB IN THE TEASPOON?

Many recipes call for fresh herbs, such as oregano, thyme, parsley, and so on. But sometimes all I have on hand is the dried herb. Is there a rule of thumb for how much dried herb to use as a substitute for the fresh?

Unfortunately, there can be no dependable rule of thumb because herbs differ so much from one to another. But the following considerations may give you a few clues. Remember that it’s not the amounts of fresh or dried vegetable matter that count in flavoring, but the amounts of essential oils they contain, because that’s where the flavor is.

The leaves of herbaceous plants are 80 percent to 90 percent water by weight. At 80 percent water, 100 grams of leaf should contain 20 grams of dry matter, so the dried herb is five times more potent. In using this dried herb, then, you would use one-fifth the weight of the fresh herb. At 90 percent water, the fresh-to-dry factor is ten, so for that dried herb you would use one-tenth the weight of the fresh. All of this assumes, however, that the only thing lost in the drying process is water, and no volatile oils—and that’s a rather shaky assumption.

The problem is that in the kitchen we generally measure herbs not by weight but by volume (teaspoons or tablespoons). Volume depends on the physical forms of the fresh and dried herbs—whole leaves, withered leaves, minced pieces, powder, and so on—and the volume ratios are therefore pretty unpredictable.

Thus, short of taking your herbs to a laboratory, having them analyzed for their percentages of essential oils, and then weighing them out, there can be no rule of thumb for how much volume of dried herb to use instead of the fresh form.