Molecular Gastronomy: Exploring the Science of Flavor (40 page)

81

Where the aroma overtakes the alcohol.

t r a d i t ion a l l y m a d e b y a d d i n g a l c o h o l to fresh, unfermented

grape juice, the
cartagène
of Languedoc has never enjoyed the reputation of the

Pineau des Charentes or other
mistelles,
as such apéritifs are known in France.

Nonetheless, its producers sought to obtain a protected designation of origin,

which meant that it had to be more precisely characterized and its method of

production codified. At the request of the manufacturers, Jean-Claude Bou-

let and his colleagues at the Institut National de la Recherche Agronomique

(inra) Pech Rouge-Narbonne station studied the importance of the grapes

used and the conditions of maturation.

In
mistelles,
the fermentation of grape juice is blocked by the addition of

brandy (equal to one quarter of the volume, hence the name
cartagène
). The

strong concentration of alcohol (at least 16%) prevents the microorganisms

that normally bring about the alcoholic fermentation of grape juice into wine

from developing.

Yet the taste of alcohol in young
mistelles
is too strong, almost like pure

brandy. To obtain a more pleasing result, producers favor a slow and limited

oxidation of the polyphenols (molecules containing benzene groups in which

several carbon atoms are bonded with hydroxyl groups, themselves composed

of an oxygen atom linked to a hydrogen atom), tannins, and other molecules

extracted from the grape during the short period of maceration (or steeping)

that follows pressing. This oxidation process resembles the one responsible

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for the softening of tannins in wines and results from reactions with the small

quantity of oxygen that is inevitably present in fermentation vats.

To study the oxidation of
cartagènes,
the inra oenologists made sample

batches of the apéritif in a cellar laboratory using three grapes: Syrah, Gre-

nache, and Cinsaut. There were ten carefully controlled phases of production:

removing the stalks from the grapes; macerating the skins in the grape juice

for four hours at room temperature; pressing; fining; leaving the wine to settle

for two to three days at a temperature of 5°c (41°f); racking, or drawing off clear

wine from the sediment; adding high-quality white brandy to the wine; storing

the mixture for a month; a further round of clarification; and, finally, aging

the wine in a stainless steel vat or an oak barrel that used to contain cognac.

The inra team avoided sulfiting (the addition of sulfur dioxide, often used in

wines to kill microorganisms or to take advantage of its antioxidant properties)

and included a maceration step to extract the most aromatic molecules and

polyphenols from the skins. Finally, the researchers compared other
cartagènes

produced by Languedoc wine growers from (white) Bourboulenc and (red) Ali-

cante grapes with the laboratory batches.

Useful Aˆng

The
cartagènes
produced in the lab were subjected to physical and chemical

analysis and sampled by a tasting jury after different maturation periods. The

oxidation of certain initial molecules was obvious: The color of the liquid—

white if made from white grapes, red if from red grapes—gradually became

uniform. Chemical analysis showed that the polyphenols and tannins were a

bit more abundant in casks than in vats. Despite the use of old barrels that had

previously contained brandy, exchanges still occurred between the
cartagène

and the wood, yielding various polyphenols.

During the testing phase, the tasters did not notice these various polyphe-

nol concentrations. By contrast, they were very sensitive to the differences be-

tween young and aged batches. In
cartagènes
held for only six months, the one

made from Syrah was appreciated for its fine red color and its fruity, nonoxida-

tive character; the ones made from Grenache and Cinsaut were less colored

and less aromatic, displaying no perceptible differences associated with the

mode of maturation. In all three cases the alcohol was very much in evidence,

indeed harsh. Yet after fifteen months no difference could be detected between

270 | investigations a nd mod el s

batches made from Cinsaut that had been aged in casks and those aged in vats;

the difference was small in the case of Grenache but larger in the case of Syrah.

All three types were sufficiently oxidized.

Were the judges’ findings reliable? The Narbonne biochemists confirmed

first the general coherence of their responses, but they observed that the tasters

fell into three groups: members of the inra station, none of them experts on

cartagènes;
producers’ representatives; and people who gave atypical responses.

Discarding the “bad” tasters of the last group, they arranged for another tasting

at which the
cartagènes
served were younger. Once again the results of the ini-

tial tasting were confirmed, but this time no difference was perceived between

cartagènes
of the same age, whether they were aged in vats or in casks.

On this round of tasting the Syrah seemed to yield a fruity and agreeable

drink more rapidly than the other groups; the
cartagènes
made from Cinsaut

and Grenache acquired a distinctive style only through limited oxidation of

polyphenols and other oxidizable molecules, but for this reason they sur-

passed the Syrah
cartagènes
in aromatic power. In all three cases aging for at

least a year was found to be indispensable. A longer aging period would in-

crease production costs, but whether it would further improve quality remains

to be demonstrated.

Cartagènes | 271

82

Tea

The chemistry of clear plaques on the surface of tea.

f o o d s a n d b e v e r a g e s contain so many amphiphilic molecules—one part

of which are water soluble and another part insoluble—that foams are common

in the kitchen: stiffly beaten egg whites, champagne, beer, cream, and so on.

In cooking one sometimes tries to minimize contact with antifoaming agents,

taking care not to spill any drops of egg yolk into whites that are about to be

whisked, for example, because the fatty molecules in the yolk bond with the

hydrophobic part of the proteins in the white, removing them from contact with

the air and thus stabilizing the water–air interface. Similarly, people who like the

fizz of champagne are careful not to wear certain kinds of lipstick that contain

antifoaming molecules. Under other circumstances, however, foam is some-

thing to be avoided. When making apricot jam, for example, one can cause the

froth created by cooking to subside by daubing the surface with melted butter.

Films Disturb Connoisseurs

A pair of chemists at Imperial College, London, both great lovers of tea, set

out to investigate the thin clear plaques that appeared on the surface of their

teacups. Michael Spiro and Deogratius Jaganyl initially supposed the plaques

to be the residue of a foaming phenomenon that had been arrested by the hard-

ness of the water, but they were surprised to find something entirely different,

which they described in an article in
Nature
.

272 |

The films that one observes in teapots and teacups are irregularly shaped

plaques that to the naked eye look like surface stains. Spiro and Jaganyl were

able to study them quantitatively once they had devised a method for collect-

ing them from the surface of large containers that they had infused with tea.

Examination of these films with a scanning microscope revealed the pres-

ence of small, clear particles on their surface that turned out to be calcium

carbonate. Microchemical analysis confirmed that all of the calcium, as well

as traces of magnesium, manganese, and other metals coming partly from

the municipal water supply and partly from the tea, could be eliminated by

treatment with chlorhydric acid. The remaining particles were organic in na-

ture and insoluble in all the solvents tested but soluble in concentrated bases.

Mass spectrometry indicated that this residue was composed of molecules of

different mass, in the neighborhood of 1000 daltons.

Spiro and Jaganyl also studied the rate of formation of these films by

infusing black Typhoo tea in water heated to exactly 80°c (176°f) for defi-

nite periods of time. After the infusion phase they removed the tea bags,

skimmed any froth from the surface, and then measured the formation of

films over time. They observed that films formed for several hours, their

quantity increasing proportionally with the number of minutes elapsed

during the first hour; after four hours, the mass of the thick film that had

formed was proportional to the surface of the container. The rate at which

the film formed depended on the atmosphere above the tea: The mass of

film that appears in atmospheres of pure oxygen is greater than that which

develops in ordinary air or under a nitrogen atmosphere. It was clear that

the film was produced by the oxidation of the tea’s soluble compounds,

certain polyphenols among them (the bitterness of tea results from such

molecules).

The British chemists did not observe any film at the surface of tea infused

in distilled water or in distilled water to which calcium chloride had been

added. A film appeared only if the water contained both calcium (or magne-

sium) and bicarbonate ions. Nor did any film form when the calcium ions

were sequestered by a chelating compound such as ethylenediaminetetraac-

etate or when the tea was acidified. No film appears in tea containing lemon,

for example, because its acidity is greater than that of unadulterated tea, its

calcium ions being sequestered by citrate ions. Similarly, very strong teas

have little film, for the abundance of polyphenols increases their acidity. By

Tea
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contrast, the addition of milk greatly increases the amount of film, as does

raising the temperature of the infusion.

The complex organic compounds found in such films, which result from

the oxidation of soluble molecules in the presence of calcium ions and bicar-

bonate ions, seem to form by a process analogous to the enzymatic oxidation

used by tea producers to transform green tea into black tea. Further research

will be needed to confirm this hypothesis.

274 | investigations a nd mod el s

A Cuisine for Tomorrow

Cooking in a Vacuum

New devices can improve traditional culinary techniques.

c o ok s f i l t e r s t o c k s t o d a y just as they did in the Middle Ages: They

put the bones and vegetable matter in a conical strainer known as a chinois (or

China cap) and press it with a pestle or a ladle to squeeze out as much liquid as

possible. Naturally the effectiveness of this procedure is limited by the size of

the mesh of the chinois. A fine cloth liner helps, but it has to be cleaned after

every filtering. Can’t we devise a more modern and efficient method? Looking

to chemical laboratories for inspiration would be a useful first step on the road

to culinary innovation.

Filtration in the Lab

The chief problem encountered in making a good stock is primarily a ques-

tion of filtration: What is the best way to make a cloudy liquid clear? Tradition-

ally clarification has been achieved by stirring a few egg whites into the cold

stock and then heating the mixture over a low flame so that, when they coagu-

late, the whites trap the solid particles suspended in the liquid. Straining the

mixture through a chinois lined with linen completes the process.

This procedure is unsatisfactory because it robs the liquid of a part of its fla-

vor. Some chefs therefore add vegetables and fresh meat, cut into small pieces,

along with the egg whites, to restore the flavor lost through clarification—a

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