What Einstein Told His Cook (26 page)

HOT WATER FREEZES FASTER!

My guests were due to arrive for a party in three hours and I needed to make some ice in a hurry. I’ve heard that hot water freezes faster than cold water. Should I have put hot water in my ice-cube trays?

T
he hot-water-freezes-faster paradox has been debated since at least the 17th century when Sir Francis Bacon wrote about it. Even today, Canadians claim that a bucket of hot water left outdoors in cold weather will freeze faster than a bucket of cold water. Scientists, however, have been unable to explain why Canadians leave buckets of water outdoors in cold weather.

But believe it or not, hot water really may freeze faster than cold water. Sometimes. Under certain conditions. It depends on a lot of things.

Intuitively, it seems impossible because the hot water simply has further to go in its downhill race toward 32°F. In order to chill down by each four degrees, a pint of water has to lose about one calorie of heat. So the more degrees the water has to fall, the more heat must be taken out of it, and that means a longer cooling time, all other things being equal.

But according to Wolke’s Law of Pervasive Perversity, all other things are never equal. As we’ll see, hot and cold water are different in more ways than their temperatures.

When cornered and pressed for an explanation of how hot water could possibly freeze first, chemists are likely to mumble something about cold water containing more dissolved air, and dissolved substances lower the freezing temperature of water. True, but trivial. The amount of dissolved air in cold tap water would lower its freezing temperature by less than a thousandth of a degree Fahrenheit, and no hot-cold race can be controlled that precisely. The dissolved-air explanation just doesn’t hold water.

A real difference between hot and cold water is that the hotter a substance is, the faster it radiates its heat away into the surroundings. That is, warmer water cools off at a faster rate—more degrees per minute—than cooler water does. The difference is especially great if the containers are shallow, exposing large surfaces of water. But that still doesn’t mean that the hot water will reach the finish line first, because no matter how fast it cools off at first, the most it can do is catch up with the cold water. After that, they’re neck and neck.

A more significant difference between hot and cold water is that hot water evaporates faster than cold water. So if we start by trying to freeze equal amounts of hot and cold water, there will be less water remaining in the hot-water container when it gets down to rug-cuttin’ time at 32ºF. Less water, naturally, will freeze in less time.

Can that really make a significant difference? Well, water is a very unusual liquid in many ways. One of those ways is that an unusually large amount of heat must be removed from water before its temperature will go down very much. (Techspeak: Water has a high heat capacity.) So even if the hot container has lost only slightly more water by evaporation than the cold container has, it may require a lot less cooling time to freeze.

Now don’t go running into the kitchen to try it with ice-cube trays, because there are simply too many other factors operating. According to Wolke’s Law, the two trays can never be identical. They are not in exactly the same place at exactly the same temperature, and they are not necessarily being cooled at the same rate. (Is one closer to the cooling coils in the freezer?) Moreover, how are you going to tell exactly when the water freezes? At the first skin of ice on top? That doesn’t mean that the whole tray full has yet reached 32ºF. And you can’t peek too often, because opening the freezer door can cause unpredictable air currents that will affect the evaporation rates.

Most frustrating of all, undisturbed water has the perverse habit of getting colder than 32ºF before it freezes. (Techspeak: It super-cools.) It may refuse to freeze until some largely unpredictable outside influence perturbs it, such as a vibration, a speck of dust, or a scratch on the inside surface of its container. In short, you’re running a race with a very fuzzy finish line. Science isn’t easy.

But I know that won’t stop you. So go ahead and measure out equal amounts of hot and cold water, put them in identical (ha!) freezer trays, and don’t bet too much on the outcome.

HUMPTY DUMPTY NEVER HAD IT SO BAD

Can raw, whole eggs be frozen? I have almost two dozen eggs that I won’t be able to use up before I go on a trip and I’d hate to have them go to waste.

I
hate to see food go to waste too, but in this case freezing the eggs might cause more trouble than they’re worth. For one thing, the shells will probably crack because, as you might expect, the whites expand when they freeze, just as water does when it turns to ice. There’s nothing you can do about that. There may also be some deterioration of flavor, depending on how long you keep them in the freezer.

More troublesome is the fact that the yolks will be thick and gummy when you thaw them out. That’s called gelation—the formation of a gel. It happens because as the eggs freeze, some of the proteins’ molecules bind themselves into a network that traps large amounts of water, and they can’t unbind themselves when thawed. The thickened egg yolks won’t be very good for making custards or sauces, where smoothness of texture is important. Using thick-yolked eggs in other recipes can be risky, and if a recipe bombs, you’ll be wasting a lot more than a few eggs.

Next time, leave them in the fridge if your trip isn’t going to last more than a couple of weeks, or hard-cook them all before you leave.

Manufacturers of prepared foods use tons of frozen eggs in making baked goods, mayonnaise, and other products. The gumminess is prevented by adding 10 parts of salt or sugar to every hundred parts of shelled, beaten eggs before they are frozen. I suppose you could do that too if you wanted to take the trouble, but the salt or sugar would sure limit your use of the eggs.

BURN, BABY, FREEZE!

What actually happened to food that is freezer-burned?

“F
reezer burn” has to be one of the more ridiculous oxymorons going. But take a good look at that emergency pork chop that’s been in your freezer much longer than you ever intended. Doesn’t its parched and shriveled surface look as if it had been seared?

The dictionary tells us that
seared
doesn’t necessarily refer to heat; it means withered or dried out, no matter what did the drying. Notice that the patches of “burn” on your forlorn pork chop are indeed dry and rough, as if all the water had been sucked out.

Can the cold alone make frozen foods dry out, especially when the water is in the form of ice? Yes indeed. While your hapless chop was languishing in the freezer, something was stealing water molecules from its icy surface.

Here’s how water molecules, even when firmly anchored in solid ice, can be spirited off to another location.

A water molecule will spontaneously migrate to any place that offers it a more hospitable climate. And to water molecules, that means a place that’s as cold as possible, because that’s where they will have the least amount of heat energy, and “all other things being equal” (see Wolke’s Law of Pervasive Perversity on page 209), Nature always favors the lowest energy. So if the food’s wrapping isn’t absolutely molecule-tight, water will migrate through it, from the ice crystals in the food to any other location that happens to be the tiniest bit colder, such as the walls of the freezer. (That’s why nonfrost-free freezers have to be defrosted.) The net result is that water molecules have left the food, and the food’s surface is left parched, wrinkled, and discolored. Burned-looking.

This doesn’t happen overnight, of course; it’s a slow process that takes place molecule by molecule. But it can be slowed to practically zero by using a food-wrapping material that blocks wandering water molecules. Some plastic wraps are better at this than others.

Moral No. 1: For the long-range keeping of frozen foods, use a wrapping material specifically designed for freezing because of its impermeability to migrant water molecules. Best of all are vacuum-sealed, thick plastic packages like Cryovac, which are quite impermeable to water vapor. Freezer paper is obviously good; it has a moisture-proof plastic coating. But ordinary plastic food wraps are made of various materials, some better than others. Polyvinylidine chloride (Saran Wrap) is the best, and polyvinyl chloride(PVC) is also good. Read the fine print on the plastic wrap package to learn what it is made of. Thin polyethylene food wraps and ordinary polyethylene food-storage bags aren’t very good, but polyethylene “freezer bags” are okay because they’re unusually thick.

Moral No. 2: Wrap the food tightly, leaving no air pockets. Any air space inside a package will allow water molecules to float through it to the inner wall of the wrapping where it is colder, and settle there as ice.

Moral No. 3: When buying already-frozen foods, feel for ice crystals or “snow” in the space inside the package. Where do you think that water (to make the ice) came from? Right: the food. So either it’s become dehydrated from being kept too long in a loose package or it’s been thawed, which releases juices from the food, and then re-frozen. In either case, it’s been abused and, while still safe to eat, will have an off flavor and poor texture.

BLOWING HOT AND COLD

Why does blowing on hot food cool it?

A
s we have all learned from experience when the etiquette police were looking the other way, the cooling of hot food by blowing on it works best with liquids, or at least with wet foods. You won’t substantially diminish the heat of a hot dog by blowing on it, but hot tea, coffee, and soup are notorious for inspiring such gauche table manners. In fact, it works so well that there must be something more going on than the mere fact that the blown air is cooler than the food.

What’s going on is evaporation. When you blow, you’re speeding up the evaporation of the liquid, just as blowing on nail polish dries it faster. Now everyone knows that evaporation is a cooling process, but almost no one seems to know why.

Here’s why.

The molecules in water are moving around at various speeds. The average speed is reflected in what we call the temperature. But that’s only an average. In reality, there is a wide range of speeds, some molecules just poking along while others may be zipping around like a Taipei taxi. Now guess which ones are most likely to fly off into the air if they happen to find themselves at the surface. Right. The zippy, high-energy ones. The hotter ones. So as evaporation proceeds, more hot molecules are leaving than cool ones, and the remaining water becomes cooler than it was.

But why blow? Blowing on the surface speeds up evaporation by whisking away the newly evaporated molecules and making room for more. Faster evaporation makes faster cooling.

Miss Manners just doesn’t appreciate some of the applications of science to gastronomy.

I
N
C
HEMISTRY
101 we all learned that matter comes in three physical forms (Techspeak: states of matter): solid, liquid, and gas. And so do our foods, although most of our foods aren’t purely one or the other.

Stable combinations of solid and gas are called foams and sponges, porous solid structures filled with bubbles of air or carbon dioxide and usually made by beating and whipping. Think of breads, cakes, meringues, marshmallows, soufflés, and mousses. If it can soak up large quantities of water without dissolving, as breads and cakes do, it’s a sponge, whereas if it breaks down and dissolves in water as a meringue does, it’s a foam.

Stable combinations of two liquids that don’t ordinarily mix, such as oil and water, are called emulsions. In an emulsion, one of the liquids is dispersed through the other one in such tiny globules that they stay suspended and don’t settle out. The prime example is mayonnaise, a flavored mixture of vegetable oil, egg or egg yolks (which are half water), and vinegar or lemon juice. It is made by adding the oil gradually and beating it vigorously into the watery egg and vinegar mixture. The oil breaks down into tiny droplets that will not separate from the egg and vinegar.

Beverages are foods in the liquid state. They are invariably water-based, but may contain various amounts of another liquid: ethyl alcohol, also known as grain alcohol because it is most easily and economically produced by fermentation of the starches in grains such as corn, wheat, and barley. Fermentation, from the Latin
fervere
, meaning to boil or bubble, is the chemical breakdown of an organic substance by enzymes released by bacteria and yeasts while feeding on it. Various types of fermentation produce various products, but the word is most often used for the conversion of starches and sugars into ethyl alcohol and bubbles of carbon dioxide gas.

Alcohol fermentation has been used for making beer from starches and wines from fruit sugars for at least ten thousand years. Our earliest ancestors quickly discovered that all they had to do was leave some crushed grapes or other fruits around in a warm place and the juices would ferment, developing an intriguing intoxicating quality.

In this chapter we will look at three main types of beverages: hot water extracts of plant materials; beverages containing carbon dioxide gas, whether naturally present from fermentation or deliberately added because we get a kick out of its fizziness; and beverages containing alcohol, whether directly from fermentation or deliberately enhanced by distillation to provide a bigger kick of a different sort.

On, then, to our coffees, teas, sodas, Champagnes, beers, wines, and spirits.
Skoal!

HAVE A CUPPA’

DON’T BLAME THE COFFEE

Can you tell me how to find the lowest-acid coffee? I’m looking for something that isn’t bitter and won’t tear my stomach apart.

A
cidity often gets a bum rap. Maybe it’s because of all the television commercials for drugs designed to control heartburn and acid reflux. But the acid in our stomachs (hydrochloric acid) is thousands of times stronger than any acid you’ll find in coffee. It’s only when the acid gets out of the stomach, splashing up into the esophagus, that it burns. In some people, coffee makes that happen, but it’s not the coffee’s acid that’s burning; it’s the stomach’s.

Several of the weak acids in coffee are the same as those found in apples and grapes, and are not at all stomach-upsetting. But if you’re still not convinced, most of these acids are volatile and are released upon roasting, so it may surprise you to know that the darkest roasts may have the lowest acid content.

The citric, malic, acetic, and other acids in coffee add liveliness to the flavor, not bitterness. Acids in general are not bitter; they’re sour. Caffeine is bitter, but it contributes only about 10 percent of the bitterness in coffee. And don’t turn your nose up at bitterness; it’s an important flavor component of coffee, just as it is in the other two essential food groups, beer and chocolate.

So forget about acid, and just find a coffee you like. If all coffees “tear your stomach apart,” I don’t have to tell you what to do. Just say “No.”

JANGLED BELLE

When my wife has a cup of espresso, she’s high for hours. Does espresso contain more caffeine than regular coffee?

I
t depends. (You knew I was going to say that, didn’t you?)

A direct comparison is complicated by the fact that there is no such thing as “regular coffee.” We have all had everything from vending-machine dishwater to truck-stop battery acid. Even at home, there are so many ways of brewing coffee that no generalizations can be made.

And let’s face it: In our current Starbucks-struck society, what goes by the name of espresso in every neighborhood joint that can scrape up the price of a machine and a minimum-wage teenager to run it would make a professional Italian
barista
(espresso maker) cry in his
grappa
. So there’s not much consistency there, either.

Any espresso is, of course, a lot smaller in volume than a standard cup of American coffee. But does the espresso’s high concentration more than make up for its small volume?

Each drop of liquid in a typical one-ounce shot of espresso certainly contains more caffeine—and more of everything else, for that matter—than a drop of liquid from a six-ounce cup of regular coffee. But in many instances, the entire cup of well-brewed American coffee will contain more total caffeine than the cup of espresso. (Notice that I said “well-brewed.” I’m not talking about that brown water they call coffee at your office, which may contain not only a tiny amount of caffeine but a tiny amount of coffee.)

What do the experts say? The consensus of Francesco and Riccardo Illy in their beautifully illustrated coffee-table book
From Coffee to Espresso
(Arnoldo Mondadori Editore, 1989) and of Sergio Michel in his book
The Art and Science of Espresso
(CBC srl Trieste, undated) is that a typical cup of good espresso can contain from 90 to 200 milligrams of caffeine, while a cup of good American coffee will contain from 150 to 300 milligrams. As you can see, there may be some overlap, but on the average, espressos contain less caffeine.

The amount of caffeine in any cup of coffee depends first of all on the type of coffee bean it was made from. Arabica beans contain an average of 1.2 percent caffeine, while Robusta beans contain an average of 2.2 percent and as high as 4.5 percent. But unless you’re a connoisseur, you may not know the types of beans in your brew, either at the local espresso bar or in your home blend. The odds are that both are primarily Arabica beans, because Arabica constitutes three-quarters of the world’s coffee production, although there is currently a shift toward more Robusta for economic reasons.

What’s important, of course, is how much of the caffeine dissolves out of the beans and into the water during brewing. That depends on several factors: how much ground coffee is being used, how finely it is ground, how much water is being used, and how long the water is in contact with the coffee. More coffee, finer grounds, more water, and longer contact time will all extract more caffeine. That’s where the differences between espresso and other brewing methods come in.

Espresso coffee is ground finer than the drip grind you may be using at home. But on the other hand, for approximately the same amount of grounds per cup, only about one ounce of water contacts the grounds during espresso-making, compared with about six ounces of water per regular cup. Moreover, the water is in contact with the grounds for only about thirty seconds in the espresso process, rather than a couple of minutes in most other brewing methods.

The result is that in your local coffee establishment you will probably imbibe less caffeine in your single shot of espresso or in your Tall Latte or Tall Cappuccino than in your Americano. On the other hand, all bets are off with the Grande and Venti Lattes and Cappuccinos, which are made with two shots of espresso.

Now about your wife: Why is she so high-strung after a cup of espresso? For one thing, it may be her metabolism, that human variable that no simple chemical analysis for 1,3,7-trimethylxanthine, aka caffeine, can explain. There are great variations in the rates of caffeine metabolism among individuals, and according to the Illy book, women tend to metabolize it faster. But that would apply, of course, to any coffee.

I’m not a physician or nutritionist, but I suppose it’s possible that in some people the caffeine is metabolized faster when it is concentrated in a small amount of liquid than when it is dispersed throughout a larger volume. On the other hand, a friend tells me that she gets more sleeplessness and more of a “jangly” feeling from her regular coffee than from an espresso.

In the absence of a series of controlled physiological studies on the effects of many kinds of espresso compared with many kinds of other coffee, all consumed both with and without food at various times of day, no one can generalize that espresso causes more caffeine excitability than American coffee. In fact, on the average, it’s probably the other way around.

Tell that to your wife when she comes down off the ceiling.

THE DECAF CHRONICLES

Are the chemicals used in decaffeinating coffee really safe? A chemist told me that they’re related to cleaning fluid.

R
elated, yes, but different. Like my Uncle Leon. In chemical families, as in human families, there are both similarities and idiosyncrasies.

Caffeine itself, for example, is a member of the alkaloid family of powerful plant chemicals that includes such bad actors as nicotine, cocaine, morphine, and strychnine. But then again, tigers and pussycats belong to the same family. The methylene chloride that’s used in some decaffeinating processes is related to, but quite different from, the toxic perchlorethylene used in dry cleaning. But it’s still no pussycat.

Chemists have identified from eight hundred to fifteen hundred different chemicals in coffee, depending on whom you ask. As you can imagine, removing the 1 or 2 percent of caffeine without ruining the flavor balance of all the others is no small trick. Caffeine dissolves easily in many organic solvents such as benzene and chloroform, but those are obviously out because they’re toxic. (No, chloroform wouldn’t cancel the caffeine’s effects by putting you to sleep.)

Since 1903, when a German chemist named Ludwig Roselius lost sleep over how to remove the caffeine from coffee and finally settled on methylene chloride, that has been the solvent of choice. It dissolves other components minimally and vaporizes easily, so that its remaining traces can be driven off by heat. Herr Roselius marketed his coffee under the name Sanka, a word he invented from the French
sans caffeine
. Sanka was introduced into the United States in 1923 and became a brand name of General Foods in 1932.

But in the 1980s methylene chloride came under fire as a carcinogen. It is still used for decaffeinating, but the FDA limits its amount in the finished product to ten parts per million. Industry sources point out that the actual amount is less than a hundredth of that.

Caffeine is removed from the green coffee beans before they are roasted. First they are steamed, which brings most of the caffeine up to the surface, and then the caffeine is dissolved out by the solvent. To be called decaffeinated, a coffee must have more than 97 percent of its caffeine removed.

An indirect method, sometimes called the water method, is often used: The caffeine—together with many desirable flavor and aroma components—is first extracted into hot water. (Caffeine dissolves in water, of course, or we wouldn’t be worrying about its presence in our cups.) The caffeine is then removed from the water by an organic solvent, and the now caffeine-free water, with all of its original flavor components, is returned to the beans and dried onto them. The solvent never actually touches the beans.

An interesting new wrinkle is the use of the organic solvent ethyl acetate instead of methylene chloride. Because this chemical is found in fruits and, indeed, in coffee itself, it can be said to be “natural.” The label of an ethyl acetate–treated coffee may therefore claim that it is “naturally decaffeinated.” But don’t be impressed. A similar claim could be made for using cyanide, because it occurs “naturally” in peach pits.