What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (40 page)

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?

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U
nfortunately, 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.

Nevertheless, if you have to substitute dried herb for fresh and can’t spare the lab fees or the thirty-day wait for the essential oil analysis report to come back, try using somewhere between one-fourth and one-half as much of the dried herb as of the fresh kind. Of course, if you’re substituting in the other direction, use between twice as much and four times as much of the fresh herb as of the dried one. In most cases, you won’t be straying disastrously far from the Yellow Brick Road.

Okay, so I lied. That’s a rule of thumb.

I’m surprised that most bottled spices and herbs in the supermarket are not labeled with a “best if used by” date. What is their average shelf life? Also, we leave them in our nonwinterized summer cottage that stays at or below freezing much of the year. Will they survive freezing temperatures?

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W
hile there is no reliable average shelf life, checking them annually should serve your purpose. Bottled herbs and spices are thoroughly dried, and most spoilage bacteria can’t live without water, so if the containers are tightly closed the herbs and spices should last indefinitely without actually spoiling. Also, things that are completely dry can’t freeze; it’s the water in foods that freezes. So the frigidity of your cabin is irrelevant as far as damage from freezing is concerned. In fact, low temperatures will extend their useful lives by slowing down the evaporaton of aromatic compounds.

Dried spices do lose their potency over time, however. In fresh, undried herbs, the essential oils are contained in a variety of locations within the leaves, such as in intercellular cavities, specialized oil cells, oil or resin ducts, glands, or hairs. But because the cell structure is broken down in the drying process, the essential oils are closer to the surface, from where they can more readily escape.

Do the sniff test the next time you leave for the season: Crumble a bit of each one between your fingers, and if it doesn’t smell as strong as it did the preceding summer, make a note to bring a replacement on your return.

Bugs have invaded my cayenne pepper and are seemingly swimming blissfully around in the hot stuff. I couldn’t believe my eyes! Did they invade my mace, paprika, or other milder spices? No! Just the cayenne. How do they suffer the hotness?

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I
t’s just another case of biologically different strokes. Differences among animal species can be enormous. There’s no reason to expect pests to behave like humans just because humans sometimes behave like pests.

The “heat” of cayenne and other hot peppers comes from chemicals called capsaicinoids (see p. 334). In humans and other mammals they irritate the mucous membranes of the mouth (and other mucous membranes at a later time, but we won’t go there).

The “heat” sensation comes primarily from the stimulation of our trigeminal nerves, which also react to pain and heat. Although I’m not an entomological neurologist (is anybody?), I’d be willing to bet my jalepeño that insects don’t have trigeminal nerves. On the other hand, their antennae react to stimuli that we humans can’t even imagine, so let’s not feel too superior in the sensory department.

There are quite a few species of insect that infest spices and other dried foods. By all means, immediately discard any spices that appear to be infested before the little devils spread throughout the kitchen—or the whole house. I once found some so-called cigarette beetles (
Lasioderna serricorne
) breeding in a package of imported crackers. It was a nightmare getting rid of them because they have wings, fly all over the house, and will eat almost anything, including, yes, tobacco. They’re yellowish-brown, about three millimeters long, and look almost exactly like—believe it or not—Volkswagen beetles.

Many of our spices these days are irradiated before being shipped to kill insects and their eggs. But as a precaution I put all imported spices that I’ve bought into the freezer for three or four days. Freezing will kill cigarette beetle eggs but may have no effect on other species, so don’t count on it.

The label on my bottle of barbecue sauce says it contains “liquid smoke.” Isn’t that an oxymoron?

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P
ardon me while I drink a glass of liquid ice, with cubes of solid water floating in it to keep it cold.

Ahh! That was refreshing. Now to your question.

While its name may be a bit nutty, liquid smoke is a legitimate and useful product. It adds a smoky flavor to foods without our having to go out and chop wood and build a fire and do all the rest of it.

Smoking is one of several ancient methods of curing or preserving foods, primarily meats and fish, by killing pathogenic microorganisms. Other long-used methods are drying (think jerky), salting (think
bacalao
or salt cod), and pickling (think . . . well, pickles). Drying works because bacteria can’t grow without moisture, salting works because the salt draws water out of the bacteria’s cells and dehydrates them, and pickling works because bacteria can’t thrive in acidic environments such as vinegar. Smoking works because the smoke contains many bactericidal chemicals. Our ancestors discovered these methods empirically, of course, long before there was any knowledge of pathogenic microorganisms.

Wood smoke can be lethal not only to bacteria but, as all firefighters know, to humans as well—if there is enough of it. When we’re exposed to only a little bit of it, however, we love its aroma (think fireplace on a winter’s night) and its flavor (think smoked trout). But smoke is a mixture of hot gases and microscopic suspended particles, which are more difficult than a genie to capture and put into a bottle. So the food industry invented liquid smoke and not only uses it in prepared foods but bottles it and sells it for home use. You may be able to find liquid smoke in 4-ounce bottles under the brand name Colgin, in pecan, mesquite, hickory, and applewood flavors.

In a traditional smokehouse, meat is hung from the ceiling, and smoke from an outside fire of moist sawdust is blown in through ducts. In modern commercial smoking plants, the density of smoke, the temperature, and the humidity are all carefully controlled to produce specific effects.

Today, commercial smoking is done in either of two ways: cold smoking, in which the food isn’t allowed to exceed 90 to 100°F (32 to 38°C), and hot smoking, in which the food can reach 200°F (93°C) or higher, and be partially cooked. Some processed meats are hot-smoked and are therefore considered to be cooked (bologna), while others are cold-smoked and sold raw (bacon). Smoked hams may or may not require further cooking; the labels will tell you.

Sausages are a real challenge to classify. The ground meat may be fresh or cured (with nitrites, for example); the filled casings may then be cooked or not, smoked or not, dried or not, and/or fermented or not. In a belt-and-suspenders precaution against bacterial contamination, frankfurters are usually cured, cooked, and smoked, while Italian salami is usually cured, fermented, and then dried. Fresh (uncooked) pork sausage, on the other hand, is neither cured nor smoked.

Vegetables can also be smoked, with mouth-watering results. In the village of La Vera in the Extremadura region of western Spain, I watched bright red
Capsicum annuum
(chili) peppers being simultaneously dried and smoked in long, low, two-level bungalows. The peppers were piled on wooden-slat platforms several feet above smoldering oak logs on the concrete floor below. The dried and smoked peppers were then ground to a velvety brick-red, paprika-like powder called
pimentón
, which has a smoky, sultry flavor. They make it in two varieties,
picante
(“sharp” or hot) and
dulce
(“sweet” or mild), depending on the “heat” of the pepper crop.

(A historical note: Although the New World’s capsicum peppers found favor here and there in Europe after Columbus brought them back, it was the Hungarians who picked up the ball and ran with it. Still renowned today for their use of paprika, they reputedly adopted it when King Carlos V of Spain sent some
pimentón
to his sister, Queen Mary of Hungary, who thought it was great stuff and spread the word. Hungarian paprika doesn’t have the rich, musky flavor of
pimentón
, however, because its peppers are dried without smoke.)

Inevitably, much of a commercial smokehouse’s smoke eventually finds its way up the stack to pollute the atmosphere. And in today’s environmentally conscious society, where there’s smoke there’s ire. Liquid smoke to the rescue!

To make it, one first generates real smoke by burning moist hardwood chips or sawdust. The moisture partially deprives the fire of oxygen to ensure maximum smokiness. The smoke is then blown at chilled condensers, where many of its chemical components (hundreds of different chemicals have been identified in wood smoke) condense to a brown liquid, which is then purified to remove undesirable—and toxic—components. What remains is usually mixed into acetic acid (vinegar) and can be added in that form to your barbecue sauce.

The FDA doesn’t permit a food to be labeled “smoked” unless it has been exposed directly to real smoke from burning wood. Read the label on the package of your favorite hot dogs; some are only “smoke flavored” by having been sprayed with or dipped in liquid smoke.

Now, you have undoubtedly been unable to forget what I said earlier about smoke’s having toxic components, and you’re wondering whether liquid-smoke-flavored foods are safe. Well, what should I say?