Chemical analysis determines when they are entitled to a protected designation of origin.
IN RECENT YEARS THE PRODUCTION of Spanish hams has risen to almost 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 distinctive 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 environment, 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 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 temperature fluctuations. To successfully adapt traditional methods to modern production 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 degradation 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 precursors of these aromas? In 1990 the Cáceres team set out to analyze the modification 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 aromatic molecules.
Two types of reaction could account for this transformation. Maillard reactions between amino acids and sugars, which are responsible for the flavors of grilled meat, bread crusts, and roasted coffee, are also produced during prolonged storage of food products, causing them to darken in color. Strecker degradations—reactions of amino acids with acids, such as the fatty acids released 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 proportionally 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 trace their origin. The most abundant ones were found to be are alkanes, molecules that are composed exclusively of carbon and hydrogen atoms. In Spanish 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 the highest seal of quality, for the meat of Spanish pigs is marbled with fat that contains many such acids.