Molecular Gastronomy: Exploring the Science of Flavor (13 page)

turned out to be negative, were initially published in the
Vigneron champenois
.

Michel Valade, Isabelle Tribaut-Sohier, and Frédéric Panoïotis had the ad-

vantage of being able to institute reliable controls that few of us have, par-

ticularly access to an ample supply of bottles of champagne from the same

vintage, differing from one another as little as possible. To simulate con-

sumption, the bottles were partly emptied, either by a third or by two-thirds.

Some were left open; others were equipped with the famous teaspoon, silver

or stainless steel depending on the case; still others were stopped with a cork;

and a final batch was sealed by a metal crown cap. All the bottles were placed

in an upright position at a temperature of 12°c (54°f). In order to test the

quantity of residual gas, pressure, loss of weight, and taste were measured at

regular intervals.

74 |

Pressure Variations

The pressure of the champagne at the outset was about 6 bars. As the bot-

tles were emptied, the pressure fell to 4 bars when the residual volume was 50

centiliters ( 16.9 oz.) and to 2 bars when the volume was 25 centiliters (8.5 oz.).

Subsequently, the drop in pressure was similar for all the bottles that had been

left open, with or without a teaspoon; it was less for the bottles with caps (10%,

instead of 50% in the case of bottles left open for forty-eight hours).

To forestall criticism of these preliminary measurements from skeptics at-

tached to the myth of the teaspoon, the researchers also measured the loss of

weight through degassing. Once again the weight loss was observed to be iden-

tical for the open bottles and for those whose neck was fitted with a teaspoon.

By contrast, the loss was zero for the bottles that had been stopped with a cork.

Although a little gas escapes from the liquid in this case, its accumulation on

top of the liquid limits any further release; when the bottle is uncorked the

next time for measurement, the noise of its being opened reveals the presence

of this accumulated gas, but the quantity of dissolved gas remains greater be-

cause the cork stopper limits the degassing of the wine.

In Vino Veritas

These measurements confirmed that degassing depends chiefly on the

pressure exerted downward on the liquid, the presence of suspended matter in

it, and imperfections in the inner surface of the bottle. This last effect is clearly

visible when one puts sand in a glass of champagne or when champagne is

poured into a frosted glass: bubbles immediately form in great numbers, trig-

gered by the irregularities introduced in the liquid.

Saving the best for last and for themselves, the Epernay researchers tasted

the contents of the various opened bottles. This blind tasting confirmed that

the teaspoon did nothing to preserve the sparkling character of the cham-

pagne. By contrast, the samples that had been preserved in hermetically sealed

bottles were more effervescent. In every case the wines had oxidized because

oxygen had been let in when the bottles were partly emptied. But never mind

that cork stoppers preserve champagne better than teaspoons; one should not

put off until tomorrow what one can do today. Once you’ve opened a bottle,

finish it off!

Of Champagne and Teaspoons
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19

Co‡ee, Tea, and Milk

Determining the most efcient way to cool down a drink that is too hot.

t h e m o s t c o m m o n e v e r y d a y e x p e r i e n c e s give rise to practical

questions. Is it true that running, rather than walking, under the rain will keep

you drier? Does it really feel cooler to wear white clothes on a sunny day? Does

water always drain out from a bathtub in a clockwise direction in the Northern

Hemisphere? Testing such questions experimentally is a simple matter, but we

are rarely willing to go to the trouble.

Small mysteries of this sort abound in cooking. Take the coffee we drink

every morning. It is always boiling hot, and we are never sure how to cool it

down. Some great minds have taken an interest in the question, including

the British physicist Stephen Hawking. According to Hawking, if you want

to avoid burning your mouth you should wait a few moments before adding

sugar, assuming you sweeten your coffee, because it will cool down more rap-

idly than if you add the sugar right away.

What is the theoretical basis for this prediction? Stefan’s law, which stipu-

lates that the heat radiated by a body per unit of time is proportional to the

fourth power of its absolute temperature, tells us that hot bodies radiate more

energy than cold bodies. In allowing the coffee to cool down by itself one prof-

its from its higher temperature, and therefore from its more intense radiation;

dissolving the sugar afterward completes the process. Putting the sugar in first,

on the other hand, has the effect of immediately cooling the coffee, so less ad-

vantage is derived from its radiation. This is plausible enough, but is it true?

76 |

Theory to the Test

Experiments (all the ones mentioned here were done under controlled

conditions that very closely reproduce actual experience) show that the effect

predicted by Hawking is too weak to be observed. Moreover, they reveal that

the cup plays an important role: As cooling begins, the cup is reheated, but

because it gives off heat only by conduction its temperature falls less rapidly

than that of the liquid, whose cooling it subsequently retards.

What if one were to add cold milk instead of sugar? Once again the experi-

ment could hardly be simpler: Make a very hot cup of coffee, then add milk at

room temperature and measure the rate of cooling. Next, compare this result

with what happens when a very hot cup of coffee is allowed to cool beforehand

and room temperature milk added at a later stage.

This time the theoretical prediction is correct. For 20 centiliters (6.75 oz.) of

boiling coffee that is cooled initially with 7.5 centiliters (2.5 oz.) of room tem-

perature milk, a comfortable drinking temperature of 55°c (131°f) is obtained

after about 10 minutes, but if one waits for the coffee to reach 75°c (167°f)

before adding the milk, one obtains the same result after only four minutes.

Knowing an elementary law of physics reduces the wait by more than half.

Teaspoon and Radiator

Where does this leave those who take neither sugar nor milk? Should they

put a teaspoon in their coffee, reasoning that the heat of the coffee will travel

through the metal of the spoon and thence radiate into the atmosphere?

This time let’s skip theoretical calculations, however interesting they may

be (for the first time in my life I was able to use Clairaut’s equation, which as a

student I had worked so hard to learn) and use a thermocouple to measure the

actual effect instead. We will see that the effect of the teaspoon is virtually nil:

When one takes two cups containing coffee at an initial temperature of 100°c

(212°f) and puts a teaspoon in one of them, the difference in temperature after

ten minutes is less than 1°c (or 1.8°f). A teaspoon is not an efficient radiator,

even when it is made of silver.

Coffee cools slowly, but what about tea? The difference in color between

coffee and tea affects the degree of radiation in principle, but in practice it does

not affect the rate of cooling because the effect is too small to be experimentally

Co¤ee, Tea, and Milk
| 77

observed: Assuming identical cups and identical quantities of liquid, the cool-

ing curves coincide exactly. On the other hand, a large bowl of tea may cool

more slowly than a small cup of tea, but that is another story.

Let’s conclude by examining the intuitive behavior of drinkers of hot bev-

erages everywhere. Is blowing on coffee an efficient way of cooling it? What

about stirring it with a spoon? Experiment shows that a boiling liquid that

cools spontaneously by 6°c (11°f) per minute cools by 11°c (20°f) per minute

when one stirs and one blows on it at the same time. Which is more effective:

stirring or blowing?

Stirring has two effects: It makes the temperature of the liquid throughout

the cup uniform and, by bringing the hottest part up to the surface, accelerates

cooling. Stirring therefore increases the area over which energy is exchanged

between the hot liquid and the cold air. A further consequence of this ven-

tilation is that it expels from the liquid the fastest-moving molecules, which

have now entered into the steam phase. This means that they are not recycled

through the rest of the liquid, with the result that its average molecular kinetic

energy is reduced. Because temperature measures exactly this, the average

velocity of molecular agitation, a lower velocity means that the liquid has

cooled. Let’s blow vigorously on the coffee in one cup while vigorously stirring

the contents of another cup, trying in the latter case to maximize the surface

area of contact between air and liquid, as the theoretical description of the

problem requires.

Question: What will we observe? Answer: Blowing is much more efficient

than stirring. The same coffee that loses 6°c (11°f) per minute when one blows

on it cools down only by 3.5°c (6°f) when it is stirred.

78 | secrets of the kitchen

The Physiolo³ of Flavor

Food as Medicine

Our primate cousins vary their diet depending on their state of health.

t o t h e g r e e k m i n d, barbarians were people who did not change their diet

when they were sick. At the Laboratoire d’Écologie Générale of the Museum in

Brunoy, Claude Marcel Hladik and his colleagues demonstrated that under cer-

tain circumstances monkeys eat earth, or plants containing alkaloids, in order

to preserve a balanced diet—even to treat intestinal disorders. In this they are

close relatives of the civilized world.

The reaction of primates to sweet solutions is a striking feature of mam-

malian evolutionary adaptation: The larger the animal, the more efficiently it

detects sugars. Large animals, better equipped to recognize sweet foods, are

able to acquire more energy for themselves. An exception to this rule, which

holds as much for fruit-eating animals as for herbivores, is the loris
Nycticebus

coucang,
a prosimian that is insensitive to sucrose (ordinary sugar). This may

be because it must tolerate the bitter taste of insects in addition to various prey

that other monkeys do not feed upon.

A Normal Primate

Regarded in terms of their ability to perceive sweet products, humans

are normal primates: Our body mass is large, and we are very sensitive to

sweet tastes. Nonetheless, this biological basis is modulated by environmen-

tal factors. For example, perceptual thresholds for glucose and sucrose differ

| 83

between the inhabitants of tropical forests and those of grasslands. Thus the

Pygmies, who occupy forests where sugar-rich fruits are common, have a less

developed sensitivity to sweet tastes than that of peoples who live in savannas,

where plants contain less sugar.