What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (32 page)

These three pigmented chemicals are in dynamic equilibrium with one another, meaning that they are all interconvertible. Their relative amounts at any given time depend on the availability of oxygen, enzymes, and antioxidants. But none of these three colored compounds has any effect on flavor or wholesomeness. It’s purely a matter of cosmetics.

Pork and veal don’t contain much myoglobin in any form, but beef contains much more, and the markets struggle to keep it for as long as possible in the consumer-friendly, bright-red oxymyoglobin form. But how?

First of all, there must be oxygen available to convert the fresh meat’s purple deoxymyoglobin into either red oxymyoglobin or brown metmyoglobin. Which of these two will predominate depends mainly on the amount of oxygen available to the meat. When there is virtually no oxygen at all, as in vacuum packaging, the meat retains its purple deoxymyoglobin color. You’d think that would solve the brown-meat problem, but unfortunately, consumers don’t like purple; they want red. Vacuum packaging therefore has only limited uses in retail sales of fresh (not cured) meats.

When only small amounts of oxygen are available to the meat, brown metmyoglobin is the chemically favored form. That’s why the surface of beef exposed to the open air may exhibit bright red oxymyoglobin, while the oxygen-deprived meat underneath will slowly turn brown. At most retail markets, meat is packaged in rigid plastic trays overwrapped with an oxygen-permeable plastic film, usually polyvinyl chloride. The surface gets plenty of oxygen and is nice and red, but the oxygen can diffuse only so far down. The deeper you go, the browner the meat is.

And by the way, have you noticed those juice-soaked absorbent pads beneath the meat in some of those trays? They’re not just mattresses to keep the meat comfy. They’re there to absorb wetness, known in butcherese as
weep
or
purge
. Obviously, it consists of juices that have “wept” out of the meat while standing, carrying along some of its water-soluble proteins and nutrients and thereby compromising its flavor and nutritional value. You don’t want that. So choose packages whose mattresses are dry, not red with juices. A dry mattress means that the juices are still in the meat, where you want them.

There is some truth to your supermarket’s claim that the brown interior meat will turn red again when exposed to air at room temperature (refrigeration slows the transformation down). The metmyoglobin may indeed react with oxygen and revert to oxymyoglobin, but that’s a slow and incomplete process, even if you spread the meat out in a thin layer for maximum oxygen contact—and that’s obviously not a good idea on sanitation grounds. Remember, though, that you’re going to make the meat even browner when you cook it, so why bother? The heat of cooking not only browns the meat by Maillard reactions (see pp. 296–97) but encourages the conversion of oxymyoglobin to metmyoglobin.

A second major factor in the red-to-brown conversion of beef is that both the deoxymyoglobin and oxymyoglobin proteins contain a lone iron atom buried deep within each of their large, globular molecules. The iron atom is normally in what chemists call the reduced, or
ferrous
, form. But if the iron atom is changed into its oxidized, or
ferric
, form, the protein molecules lose their purple or red colors and turn brown. Antioxidant enzymes in the meat normally keep this change from happening, but if the meat is stored too long, even at refrigerator temperatures, the enzymes’ activity diminishes and browning is facilitated.

This “old-age” browning, often accompanied by an off flavor, is what people think of when they see meat that isn’t red. But as we’ve seen, browning can come also from a harmless deficiency of oxygen in fresh meat. The meat isn’t really bad until bacteria get hold of it, in which case it will probably also have an off odor. So let your nose be your umbrella. (No offense, Cyrano.)

When bacteria do take up residence on the meat’s surface either before, during, or after it has been ground, other browning—and decaying—reactions take place. Spoilage bacteria not only can turn red oxymyoglobin into brown metmyoglobin, but they can then turn the metmyoglobin into green choleglobin and sulfmyoglobin. And you already know that when you see green, your feet should beat a fleet retreat from the meat. Morever, in producing sulfmyoglobin from metmyoglobin the bacteria release hydrogen sulfide, a notoriously smelly gas.

If you’re a suspicious type, poke a hole in the meat package as soon as you leave the market. Take a sniff through the hole while you can still storm back into the market in high dudgeon. (Is there a low dudgeon?)

A quality market will watch its ground-beef supply lines carefully, grinding and putting out just enough to keep up with sales. That way, it will always be oxymyoglobin-red at the time of sale. If the meat is allowed to begin losing its bright red color, shoppers tend to reject it even if it is not old-age brownness but merely lack-of-oxygen brownness. The retailer still has to mark it down in order to move it. That can be a boon to savvy or budget-conscious consumers.

The meat industry, of course, wants to minimize these color-related losses of revenue. One oft-used preemptive tactic has been to feed the cattle vitamin E, an antioxidant, before sending them off to meet their maker. Antioxidants prevent the iron atoms in the myoglobin molecules from becoming oxidized to the ferric form.

But the industry has yet to work out what is to them a vexing economic problem: The feedlot operators have to bear the cost of the vitamin E–laced feed, while it’s the retailers who benefit from increased sales. In my opinion that’s just too bad, and I refuse to lose any sleep over it. The way things have been going, it will probably be solved when a single, huge agribusiness conglomerate owns everything from the cattle ranch to the meat cases in your supermarket. From cradle to beyond the grave, so to speak.

Or, in an alternative universe, small, local meat farmers will increase in number, so that all our meat will
be
fresh and
look
fresh, without having been shipped thousands of miles and having its colors manipulated at the marketplace.

We can dream, can’t we?

I like to try new products and bought a plastic-wrapped package labeled “Souse” in my neighborhood market. The package didn’t include even the simplest cooking instructions, nor could I find any recipes in any of my dozen-plus cookbooks. So I sliced it, coated it with cornmeal, and tried to brown it in a frying pan, as I do scrapple. The result was grease soup. What went wrong?

....

J
ust because souse and scrapple have funny names and come in refrigerated rectangular blocks doesn’t mean they’re related, except for their porcine parentage.

Scrapple, often called Philadelphia Scrapple, is a Pennsylvania Dutch concoction of cooked pork scraps and trimmings (no gruntz) called
puddin’
, mixed with cornmeal mush, a.k.a. polenta, and spices. Refrigerated, it forms a fatty cake that can be sliced and fried for breakfast. The English, as Pennsylvania Dutch people call the rest of us, make a similar product that they call, ironically, by the German name
ponhaus
.

Souse, on the other hand, is—are you ready?—pickled, spiced, and seasoned scraps from boiled pigs’ heads, feet, and ears. No cornmeal binding; it’s held together by the gelatin that forms when the pieces are cooked. When you put yours into the frying pan, it was like trying to fry Jell-O.

Also known as head cheese, souse is meant to be eaten cold (if at all). It is related to the Italian
sopressata
, which is made by boiling a de-brained pig’s head until the meat and tongue fall apart, whereupon they are cut into small pieces, seasoned and spiced, put into a cloth bag, and pressed (
sopressata
in Italian) into sausage form.

In this country, scrapple and souse are not commonly sold in upscale, “gourmet” meat markets, where the clientele may be more partial to such politically correct and trendy delicacies as free-range salami, roast suckling duck, and grass-fed trout. All to be garnished, of course, with stuffed chives. (Think about it.)

Can you tell me what that weird, rainbow-y sheen is that I see on roast beef, corned beef, and pastrami? Is my fear of it irrational, or if I can manage to get past the appearance, is it safe to eat? I haven’t eaten a deli beef sandwich in years.

....

S
hame on you. There’s nothing better than a New York–style, kosher, thin-sliced, fat-laden corned beef sandwich on rye. But the diet pendulum has a habit of swinging back and forth, so depending on whether it’s fat or carbohydrates that happens to be in the doghouse when you read this, there will be those who advise you to order your sandwich either without the meat or without the bread.

Now, about your multicolored meat: That iridescent or rainbow appearance that sliced meats sometimes take on is not a coating of nefarious mold or rot. It is merely an optical effect. You may find it on both cured meats such as ham or corned beef and uncured meats such as roast beef and pork. It’s caused by the slicing process.

Meat, or animal muscle, is made up of
myofilaments
, tiny strands of protein. They are bound together in parallel bundles to form myofibrils, which in turn are bundled together to form the fibers that make up whole muscle. When a very sharp knife or slicing machine cuts the myofilaments crosswise at a certain angle, their severed tips, which are comparable in size to the wavelengths of light, can play optical tricks. One theory has it that the translucent tips bend (
refract
) the light waves into two different directions. This optical effect is called
birefringence
or
double refraction
. The two refracted waves then interfere with each other on their way to your eye and break up into their component rainbow colors.

Or, the iridescence on a meat surface may be caused by
diffraction
, the breaking up of light by the pattern of closely spaced myofibril ends, as in a so-called diffraction grating. In either case, the colors you see are dominated by green because the human eye is most sensitive to that color.

It’s all perfectly harmless.

Why do cured meats such as ham, corned beef, and hot dogs have that bright pink color?

....

“C
uring” meat means treating it to keep it from spoiling, thereby preserving it for future use. (Interesting that the “cure” prevents, rather than treats, the problem.) Ancient methods of curing meat include smoking, drying, and salting. When refrigeration and mechanical packaging came along, these flavor-intensive methods became unnecessary and experimentation with chemical curing began.

Meats cured with pure salt (sodium chloride, NaCl) tend to turn an unappetizing brownish-gray color. But about a hundred years ago it was found that if saltpeter (potassium nitrate, KNO
3
) was added to the salt, the meat turned a nice, rosy pink. Today, we know that the potassium nitrate was being reduced to potassium nitrite (KNO
2
) by microorganisms on the meat and that it’s the nitrite that does the job. So potassium or sodium nitrite is now added to the curing salt directly, and saltpeter is rarely used. Nitrites give the meat a tangy flavor and an appetizing color, owing to the reaction of nitrite with myoglobin to form
nitric oxide myoglobin
. They also fight rancidity and the development of off odors and off flavors during storage.

But the most important function of nitrites is to inhibit the growth of pathogenic bacteria such as
Staphylococcus aureus
and
Clostridium botulinum
, the bacteria that cause botulism.

There’s only one hitch in this rosy (literally) picture: Not only does nitrite kill botulin bacteria, but in doses of about 20 milligrams per kilogram of body weight it can kill humans as well. Fortunately, much of the nitrite added during curing is decomposed by cooking.

The USDA limits the amount of residual nitrite in any finished meat product, cooked or raw, to a maximum of 70 parts per million. At that level, a 150-pound person would have to eat 43 pounds of the product at one sitting to get a lethal dose of nitrite. That’s a lot of bologna.

The bad news is that nitrites in cured meats can react with amines from the amino acids in heated meat protein to form chemical compounds called
nitrosamines
, many of which have been shown to cause cancers in experimental animals and are likely to be carcinogenic in humans as well. Bacon is a special case, because the high temperatures at which it is cooked are particularly conducive to nitrosamine formation. For that reason the USDA permits less nitrite to be used in curing bacon than in curing other meats.

Small amounts of nitrosamines occur naturally in some of our foods, such as fish. Moreover, bacteria in our mouths can change nitrate, which is present in many vegetables, to nitrite, which can then act upon the amines in the vegetables’ proteins to form nitrosamines. Nitrosamines can also be formed by the action of the highly acidic juices in our stomachs upon a wide variety of amine-containing foods. Small amounts of nitrosamines can also be found in beer and tobacco.

All this may sound frightening, but don’t give up on cured meats as a way of avoiding nitrites and nitrosamines. In our society we can’t always eat fresh meat; some meat products must be cured before being distributed widely. Their small and carefully regulated nitrite content is a winning tradeoff against the risk of botulin poisoning.