What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (4 page)
Read What Einstein Kept Under His Hat: Secrets of Science in the Kitchen Online
Authors: Robert L. Wolke
Difference number 1 means that the creamed coffee with its larger volume will take more time to cool off. That is, more heat must be removed to lower its temperature by any given number of degrees. (A bathtub of water takes more time to cool than a bucket of bathwater of the same temperature.) Difference number 2 has the same result: the slightly cooler creamed coffee will cool off more slowly than the slightly hotter black coffee, because the smaller the temperature difference between a hot object and its surroundings, the slower will be its rate of cooling. So immediate creaming wins again.
My advice is to add the cream as soon as possible. The coffee will be hotter by as much as a degree or two at drinking time, and I’m sure your life will be much the better for it.
I’m pleased to report that this problem was the subject of a careful scientific experiment led by the college student Jonathan Afilalo and published in the spring 1999 issue of the
Dawson Research Journal of Experimental Science
. This is a most impressive journal that publishes papers on original, professional-quality research by undergraduate students at Dawson College in Montreal, Quebec.
Sidebar Science:
Cooling it
THE HIGHER
the temperature of an object, the faster it will lose its heat by radiation. That’s the Stefan-Boltzmann Law. Also, the bigger the temperature difference between two objects in contact with each other (such as coffee and air, for example), the faster the hot one will lose its heat to the cooler one by conduction. That’s Newton’s Law of Cooling. There are precise mathematical formulas for both of these laws, but I see no reason to burden this page with them. I’ll return to Newton’s Law in Chapter 9.
The cooling of a cup of coffee when the cream is added two minutes after pouring (curve 1), and when the cream is added ten minutes after pouring (curve 2). Adding the cream earlier yields hotter coffee at drinking time.
The students’ experiment came to the same conclusion as I did, as shown by their measured cooling curves plotted in the graph above. In curve 1 the cream was added two minutes after the coffee had been poured, whereas in curve 2 it wasn’t added until ten minutes after pouring. Note that thereafter the temperature in curve 1 remained about a degree and a half higher than in curve 2. Early addition of cream does keep the coffee hotter.
When a calorie is not a calorie
There is a difference between what a chemist calls a calorie and what a nutritionist calls a calorie. The chemist’s calorie is the amount of heat energy required to raise the temperature of
one gram
of water by one degree Celsius, whereas the nutritionist’s calorie, the calorie you see in diet books and on food labels, is the amount of heat energy required to raise the temperature of
one thousand grams
(a kilogram) of water by one degree Celsius. Obviously, then, a nutritionist’s calorie is a thousand times bigger than a chemist’s, and the chemist would call it a kilocalorie, or kcal.
In this book I find myself in the awkward position of being a chemist writing about food for an audience that spans both camps. For consistency in this book, and if my chemistry colleagues will forgive me, I will use the word
calorie
in the nutritionist’s sense unless otherwise noted. In many cases, I use the word
calories
simply to mean an unspecified amount of heat energy, in which case the chemist/nutritionist dichotomy doesn’t matter.
For those chemists who are not appeased, here is a supply of kilos to insert in front of the word
calorie
whenever you encounter it in the book: kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo kilo.
(Note to users of the International System of units: One nutritional kilocalorie, kcal, is equal to 4.19 kiloJoules or kJ.)
| | OUR ALCOHOLIC RELATIVES | |
I know there is ethyl alcohol, methyl alcohol, and rubbing alcohol. Which of those are edible—or drinkable—and which are not? Are all alcohols born the same before they undergo various changes or additions?
....
N
o. Even though they are members of the same chemical family, there are vast and crucial differences among the alcohols, and it can be a matter of life and death to be aware of them.
Alcohols are a large family of organic (carbon-containing) chemicals that are related in two ways: their molecules contain one or more
hydroxyl groups
(OH), and they react with organic acids to form chemicals known as esters.
Scientists classify everything from animals to chemicals according to their shared characteristics—characteristics that may be of no practical interest, or even downright misleading, to nonmembers of the science guild. Fret not, therefore, that eggplant (
Solanum melongena
) and potatoes (
Solanum tuberosum
) are in the same botanical family as the poisonous deadly nightshade (
Solanum dulcamara
), or that lobsters and wood lice both belong to the family of Crustacea. But don’t we all have strange relatives? Take my uncle Leon. Please. (Apologies to Henny Youngman.)
Similarly, alcohols include the highly poisonous methyl alcohol, CH
3
OH, a.k.a. methanol or wood alcohol; the somewhat less toxic isopropyl alcohol, C
3
H
7
OH, a.k.a. isopropanol or rubbing alcohol; and the even less toxic—but still potent—ethyl alcohol, C
2
H
5
OH, a.k.a. ethanol or grain alcohol, the alcohol in beer, wine, and spirits. That’s not to mention alcohols that we never think of as alcohols, such as cholesterol, C
27
H
45
OH, and glycerol or glycerin, C
3
H
5
(OH)
3.
(As you have noticed, chemists name all alcohols with the suffix -
ol
.)
So, don’t let the name “alcohol” fool you into thinking that a chemical is relatively harmless. Dead is a lot worse than drunk.
THE FOODIE’S FICTIONARY:
Taste bud—a sip of beer
| | ALL HOPPED UP | |
The label on my beer bottle says that it’s made from “the finest hops.” What’s a hop?
....
H
ops are the dried flowers of the hop plant, known to botanists as
Humulus lupulus
. It’s a tall, climbing vine of the hemp family, and its flowers impart that mellow bitterness to beers and ales, balancing the sweetness of the malt. They also contribute a grassy flavor note and a pleasant aroma, depending on when in the brewing process they are added to the wort—the fermenting grain mixture.
In Belgium, the early spring shoots of the hop plant are a delicacy when cooked and served like asparagus.
Flower buds of the hop plant (
Humulus lupulus
).
Hops are an essential ingredient in beer.
There are some interesting sidelights to the story of the hop. For one thing, there are boy hops and girl hops. It’s the mature female flowers, because of their unique resins, that have been used for about a thousand years to flavor brews and tonics. The female plants, incidentally, do very well with no males around; their flowers simply develop no seeds and will not reproduce. Most brewers prefer their hops without seeds, so the males aren’t usually cultivated. (No aspersions intended on the males of other species.)
Practically every quality from sedative to diuretic to aphrodisiac has at one time or another been ascribed to the female hop, and it has historically been added to elixirs and concoctions intended for virtually every purpose. The bitter flavor of hops probably has a lot to do with the traditional belief that good medicine must taste bad.
Do the long-reputed sedative properties of hops have anything to do with the sleepiness that overtakes one after drinking beer? No one really knows. A gallon of beer is made with one or two ounces of hops, but it may contain four or five times as much alcohol, a well-known sedative. We’ll never know the soporific role of the hops until someone carries out the appropriate experiments with alcoholic and non-alcoholic beers containing the same amount of hops. (Looking for a school science project?)
Hops are an essential ingredient in beer, and not only for their aroma and bitterness. They clarify the beer by precipitating the proteins in the wort, and they have antibiotic properties that help preserve the beer. Among the more than 150 chemical compounds that have been identified in their essential oil are chemicals (
terpenes
) called isohumulones, which are light-sensitive. When struck by either visible or ultraviolet light, they break down into very active free radicals (see p. 175) that react with sulfur in the beer’s proteins to produce smelly compounds called skunky thiols, which the human senses of taste and smell are able to detect at levels of a few parts per trillion. They are chemically similar to the thiol compound in the glands of skunks that earns them their unsociable reputation.
Beer that has been exposed to light for as little as 20 minutes reputedly can develop a “skunky” taste. That’s why beer is packaged either in cans or in light-proof brown bottles. To be safe, then, I recommend that you not leave your beer in the glass while “nursing” it. Drink it as fast as you can.
THE FOODIE’S FICTIONARY:
Hops—neither skips nor jumps
| | Beer Batter Bread | |
S
o you think beer is just for drinking? Think again. This beer bread makes excellent toast and wonderful toasted cheese sandwiches. The flavor varies, depending on the beer you use. I tested this recipe with Pittsburgh’s hearty local brew, Penn Pilsner Dark. The bread tastes best the day it is made.
3 cups self-rising flour
3 tablespoons sugar
1 can or bottle (12 ounces) of beer, preferably not light
1.
Place an oven rack in the lower third of the oven. Preheat the oven to 350°F. Spray a 9-by-5-by-3-inch loaf pan with nonstick cooking spray.
2.
In a large bowl, mix the flour and sugar thoroughly. Gradually add the beer while stirring with a wooden spoon until no patches of dry flour are visible. (Do not overbeat or the bread will toughen.) The batter will be sticky. Transfer it to the loaf pan and spread it into the corners.
3.
Bake for 50 to 60 minutes, or until a skewer or cake tester plunged deep into the middle of the bread comes out clean. The top of the loaf will have a cobbled appearance.
4.
Turn the bread out of the pan onto a wire rack and let it cool for at least an hour. Use a sharp, serrated knife to slice. The crust will be crunchy and the interior soft and moist.
MAKES 1 LOAF
THE FOODIE’S FICTIONARY:
Sourdough—gambling losses
| | SUL-FIGHTS? | |
Why do so many wine labels say “Contains sulfites”? My husband has been told he’s allergic to them, but when we asked at the liquor store we were told that all wine naturally contains sulfites. Then why the warning? They don’t label coffee “Contains caffeine.”
....
S
ulf
ites—
not to be confused with sulf
ates
—are a family of chemical salts derived from sulfur dioxide (SO
2
). They are formed during the fermentation of wine from sulfur compounds naturally present in the grapes, so a certain small amount is indeed natural and unavoidable.
In addition, sulfites (or sulfur dioxide gas from burning sulfur) have been added to wines for thousands of years to protect them against oxidation and discoloration. Moreover, sulfites can kill harmful bacteria and wild yeast cells in the grape pressings so that the “tame” fermenting organisms can get a biologically clean start. Without the preservative effect of added sulfites, wines would not be drinkable after one or two years, which may be little problem for a wine that is best drunk young, such as a Beaujolais, but would be a tragedy for a slow-aging Bordeaux.