Why is the crust of bread tastier than the crumb? Why do you have to brush a beautiful leg of suckling lamb with oil before putting it in the oven? Why is beer that golden color? Why does roasted coffee taste so good? All these and similar questions that we can ask ourselves when walking around the kitchen can be answered succinctly with three words: Maillard reaction .
On November 27, 1911, the French chemist Louis Camille Maillard presented the results of his research at the Academy of Sciences under the title “The action of sugars on amino acids”, a communication that was read by his colleague Professor Armand Gautier and published in article form the following year. And in the same way that happened with the essential work on thermal engines by Carnot -foundation of the steam engine- or that of non-Euclidean geometry by Friedman -which laid the foundations for understanding the structure of the universe-, Maillard’s work went unnoticed . Even Maillard himself did not realize its scope, although he had the intuition that he had stumbled upon something important: «The consequences of these facts seem to me important not only in human physiology and pathology, but also in plant physiology, agronomy, geology. The mere enumeration of these consequences would be too long.
For 10 years he had worked on the synthesis of peptides, which are nothing more than the union of two or more amino acids -proteins are usually very long chains of amino acids, from 100 to several thousand-. But his secret wish was to discover the structure of proteins . And then it happened: he heated sugars and amino acids in the same container. Maillard’s reaction had just been born.
As complicated as it is, its principle is very simple. When the molecules that contain the chemical amino group, made up of a nitrogen atom bonded to two hydrogen atoms -as occurs in amino acids-, are heated in the presence of sugar, a water molecule is eliminated and both components unite forming what is called a ‘Schiff base’. This compound derives, more or less quickly, in another called ‘Amadori compound’, in honor of the Italian chemist who described it for the first time in the 1960s, Mario Amadori, from the University of Modena – right where it comes from the famous balsamic vinegar. This new compound will react with others forming ring-shaped or cyclic molecules, which chemists call aromatic because, as the name suggests, they confer “odorous” properties to the substances that contain them.
Actually, Maillard’s famous reaction is not unique. In fact , it is a complicated set of reactions that are not yet very well known and where the reaction products are numerous. In 1990 a major chemical journal devoted an article of over 20 pages to this reaction, describing the many products formed. In the kitchen, and due to the action of heat, compounds belonging to the same family as table sugar (which biochemists call carbohydrates) and amino acids react with each other, giving rise to the formation of various aromas and colours. It is produced simultaneously on hundreds of components; the combinations are innumerable, as are the products that are formed, and certain molecules, whose concentration is minimal in food, play a basic role in providing those exquisite smells and flavors of good cooking. And not only that. The Maillard reaction seems to play an unfortunately important role in different processes and diseases , such as diabetes, leprosy, aging, Alzheimer’s, opacity of the lens of the eye…
So what happens in the crust of the bread?
In the first ten minutes of cooking in the oven, the yeast accelerates its fermentation due to the increase in temperature and emits carbon dioxide. In addition, the ethanol produced during fermentation by the yeast and part of the water contained in the dough evaporate. All this makes the dough rise and expand. This process ends when the temperature of the dough reaches 56 degrees Celsius: then the yeasts die.
The crust appears when the sugars combine with the amino acids present in the dough, giving it that characteristic color and flavor of toasted cereal. When the oven reaches 130 degrees, sugars such as dextrose and maltose begin to caramelize. Meanwhile, the crust continues to heat up and will eventually reach the same temperature as the oven. But the bread is not done yet: only when it reaches an internal temperature of over 80 degrees will our dough be completely cooked.
However, you know. The next time you bite into a crispy crust bar or sauté anything in a bit of fat looking for that signature brown color, remember that both are products of the Maillard reaction, which takes place at high temperatures and hardly changes. produced by boiling food.
