Molecular Gastronomy: Exploring the Science of Flavor (23 page)

which is to say long chains of amino acids capable of being folded into a ball,

but they are also molecules carrying electrically charged groups that interact

within proteins and with charged groups of other molecules.

The current theoretical description of polymers, developed by Pierre-Gilles

de Gennes and Mohamed Daoud at the Commissariat de l’Énergie Atomique

in Saclay, predicts that the maximum lowering of interfacial tension ought to

be obtained in the case of the molecules that make up the densest adsorbed

layers. The presence of electrical charges complicates this prediction, for the

greater the charge of a protein the greater its solubility and the less dense the

adsorbed layer. By contrast, counterions, which surround the charged protein

150 | investigations a nd mod el s

groups, are supposed to weaken intramolecular and intermolecular attractions

and repulsions.

To test these predictions, the physical chemists from Nantes and Toulouse

limited their attention to caseins, which, because they do not form a ball, can-

not be unfolded (or denatured) during the formation of foams—one less mech-

anism to take into account. Comparison of various proteins revealed that for

globular and nonglobular proteins alike, interfacial tension increases with the

concentration of foaming proteins. Two populations of proteins were found to

successively appear at the water–air interface, where they constitute distinct

molecular layers. The first layer, a weak protein concentration, establishes it-

self on the surface, with the addition of supplementary proteins triggering the

formation of a second layer.

The principal difference between globular and nonglobular proteins in-

volves the structure of the molecules in the layer that is in contact with the air:

Nonglobular proteins exhibit a single conformation, whereas globular proteins

seem to divide into two subpopulations that differ in respect of the number of

amino acids adsorbed at the interface.

What lesson can chefs draw from all of this? Perhaps that they should

change their ways. There is no reason, apart from tradition, to make foams

from the full protein content of the egg. Why not use specific proteins with

superior properties? If they were to combine gelatin and water and beat the

mixture for a very long time, for example, they would find that they can obtain

quarts of a specific kind of foam from only a few sheets of gelatin. Of course,

they would have to make sure that the water they use is flavorful.

Foams
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42

Hard Sausage

Improving the quality of commercial brands requires identifying the mol-

ecules responsible for their aromatic qualities.

h a r d s a u s a g e s s u c h a s f r e n c h
saucisson
are traditionally made by

adding sugar, salt, saltpeter, herbs, and spices to a mixture of meats that is then

put into a casing and left to dry for several months. This method, which does

not rely on any fermentation agents (acidifying and aromatizing microorgan-

isms), can produce both the best and the worst results. Insufficient acidifica-

tion by bacteria naturally present in the meat carries the risk that pathogenic

microorganisms will develop. Moreover, spontaneous flora do not invariably

impart a pleasing taste to hard sausage.

In seeking to avoid this Charybdis through the use of controlled fermenta-

tion, the food processing industry sometimes falls into the clutches of Scylla:

Commercial products often are too soft (the drying process often lasts less

than a month), and many of them lack the aromatic quality associated with

artisanal sausages. This situation is changing, for commercial manufactur-

ers have an incentive to remedy these defects. In France they have charged

researchers from the Institut National de la Recherche Agronomique (inra)

station at Clermont-Ferrand with the task of determining exactly what makes

a good
saucisson
.

Jean-Louis Berdagué, Marie-Christine Montel, and Régine Talon set out to

extract, and then identify, the aromatic components of hard sausages using

high-resolution gaseous phase chromatography (whereby a carrier gas con-

veys the volatile molecules extracted from a sample into a capillary tube that

152 |

differentially retains, and therefore separates, the constituent elements of the

aroma) in combination with mass spectrometry (which identifies the compo-

nents separated by means of chromatography). Thanks to these techniques it

is now possible to characterize both the properties of the meat used in making

a sausage and the curing process itself.

The Clermont-Ferrand team observed first that the aroma of hard sausage

derives from about 100 organic compounds produced by the action of enzymes

present in the meat and the fermentation agents. Subsequent analysis of sau-

sages prepared from various bacterial combinations showed that the flora re-

sponsible for maturation play a crucial role in creating aromas.

In one experiment, six mixtures of acidifying bacteria (
Lactobacillus
and

Pediococcus
) and aromatizing bacteria (
Staphylococcus
) were used to produce

thirty different sausages (five samples per bacterial mixture). The volatile com-

pounds in these samples were then analyzed and their aromas evaluated by a

dozen trained tasters who had agreed beforehand about the terms to be used

to describe aromatic characteristics.

In a further step, a statistical analysis disclosed the relationships between

aroma and the presence of the various compounds. More precisely, the oxida-

tion of lipids was found to play a preponderant role in determining aromatic

quality: A rancid smell is associated with the presence of aldehydes, alkanes,

and alcohols, whereas the smell of good hard sausage is associated with the

presence of methyl ketones and methyl aldehydes. Finally, the degradation of

sugars favors the development of vinegar odors, created by acetic acid, or of

butter aromas, created by 2,3-butanediol.

These studies revealed a situation analogous to the what one finds in the

case of yogurt, where the quality of the final product depends on the use of

bacterial strains from wholesome milk. Making aromatically rich sausages

likewise depends on the quality of the strains used in the maturation process.

Packaging and Aromatization

Further studies carried out by the same team in Clermont-Ferrand in col-

laboration with Christine Viallon showed that both the length of the curing

process and the type of packaging affect the aromatic quality of sausage. Pro-

longed drying often leads to a loss of aroma because water evaporation carries

away with it the volatile compounds. Sausages harden as a result of drying,

Hard Sausage
| 153

however, and the progressive concentration of salt brings out their flavor. The

inra team wondered whether wrapping the sausage in plastic film would pre-

vent the loss of aroma through drying. They found that the use of film both

limits drying and strongly modifies the degradation of sugars, with the result

that products wrapped in this way are less sour and have a more buttery taste.

Finally, the mechanisms of aromatization were also studied. The Clermont-

Ferrand researchers were able to detect traces of pepper (terpenes), garlic (sul-

fur molecules), and brandy (esters formed by the reaction of ethyl alcohol with

the fatty acids produced by salting).

Commercial brands of sausage therefore may be expected in the future to

reproduce the flavor of artisanal products. Better still, recent research suggests

that synthetic aromas can be created that will improve the quality of unsatis-

factory bacterial strains. A compound such as 1-octene-3-ol, introduced in the

initial stage of fabrication by Didier Roux, a research scientist working with

Capsulis S.A., has produced sausages having a delicate aroma of
sous-bois
(wild

mushroom with hints of decomposing mossy undergrowth).

154 | investigations a nd mod el s

43

Spanish Hams

Chemical analysis determines when they are entitled to a protected desig-

nation of origin.

i n r e c e n t y e a r s t h e p r o d u c t i on of Spanish hams has risen to al-

most 30 million units per year. Some of these, obtained from Iberian pigs by

traditional methods in the southwest of Spain (more than a million hams a

year), have a taste that is so remarkable that the European Union has granted

protection to producers in their place of origin. How is this taste achieved?

Jesús Ventanas and his colleagues in the veterinary faculty of the Universidad

de Extremadura at Cáceres have examined the various stages involved in the

long process of preparing these hams and identified the reasons for their dis-

tinctive quality.

The traditional method of fabrication has a number of special features that

begin with the raising of the pigs. They are of native stock and allowed to roam

freely, feeding for the most part on acorns and herbs until their weight reaches

160 kilograms (about 350 pounds). After slaughter in the late fall, when the

cool weather prevents meat from spoiling easily, the hams are kept for two days

at a temperature of 0°c (32°f). They are then rubbed with salt containing 1%

saltpeter and placed in a bed of this salt for a week in a comparably cool envi-

ronment, 0–4°c (32–39°f). The salt is then wiped off and the hams are left to

rest within the same temperature range for two to three months before being

dried. The drying lasts for a month and a half in the spring, at temperatures

that rise finally to 18°c (64°f). During the summer the hams are stored for

| 155

another month and a half at room temperature before the final phase of the

curing process, which is carried out in cellars for a period of 14–22 months.

Historically, this very long process developed in response to the peculiar

character of the climate of the Extremadura region in Spain, but today cold

storage rooms equipped with thermostats make it possible to prevent tempera-

ture fluctuations. To successfully adapt traditional methods to modern pro-

duction techniques, producers must be able to determine not only the proper

temperature levels but also the appropriate length of time—the shorter the

better—for the various stages involved in curing the hams. Recent research

has helped them do this.

By the 1970s chemists had shown that products formed by the degrada-

tion of proteins (molecules formed by the linkage of amino acids) and lipids

contribute to the aroma of certain foods, notably cheeses. Are these products

responsible for the aroma of Spanish hams as well, or are they only the precur-

sors of these aromas? In 1990 the Cáceres team set out to analyze the modi-

fication of proteins and lipids at each stage of the traditional curing process.

They observed that the amino acids released by the decomposition of proteins

during salting subsequently became degraded, forming the precursors of aro-

matic molecules.

Two types of reaction could account for this transformation. Maillard reac-

tions between amino acids and sugars, which are responsible for the flavors

of grilled meat, bread crusts, and roasted coffee, are also produced during pro-

longed storage of food products, causing them to darken in color. Strecker

degradations—reactions of amino acids with acids, such as the fatty acids re-

leased during the degradation of lipids—produce aldehydes, which are often

aromatic.

The Secret Is in the Curing

In Spanish hams the accumulation of Maillard products increases pro-

portionally with the length of maturation, proof that good hams cannot be

obtained without long curing. Moreover, aldehydes, which are formed after

salting, also play a role in Maillard reactions, yielding products that retard the

rate at which fats become rancid.

More recently Spanish chemists have approached the problem from the

other direction by first identifying the volatile molecules and then trying to

156 | investigations a nd mod el s

trace their origin. The most abundant ones were found to be are alkanes, mol-

ecules that are composed exclusively of carbon and hydrogen atoms. In Span-

ish hams they are of two types: linear alkanes, which probably come from the

decomposition of lipids, and ramified alkanes, a consequence of the distinctive

acorn-based diet on which Iberian pigs feed. Chemistry therefore supports the

practice of awarding the protected designation of origin only to hams prepared

from animals allowed to graze freely in oak groves.

Another aromatically important class of molecules is made up of the linear

aldehydes, which are formed by Strecker reactions and by reactions associated

with unsaturated fatty acids that turn rancid. Here again chemistry justifies