In the world of food and wine pairings, nothing is more classic than matching a nice piece of grilled meat with a big red wine like Bordeaux. The two work well together, partly due to the counterpoint between the meaty flavors and the fruity character of the wine and the way the fat in the meat softens the tannins, but also because they share a number of aromatic components that come from the same source: the Maillard reaction.
The Maillard reaction is a chemical reaction between sugars and amino acids or other substances that results in browning of various sorts, notably caramelization and pyrolysis. Caramelization and pyrolysis are responsible for the crusts of breads and cakes, the charred surface of a steak, or the dark brown color and roasted notes of cocoa or coffee, to give only a few examples. (You can find more details about the Maillard reaction here and here.)
Some of the main aromatic components that make the Maillard reaction so enticing are called heterocycles, named that way because they are always based on a group of atoms (a cycle) where carbon combines with a different atom (oxygen, nitrogen, phosphorus, or sulfur). Heterocycles are small and volatile components, which means they can be highly aromatic.
The Maillard Two-Step
Some years ago, Bordeaux researcher Stéphanie Marchand, a maître de conferences at the Institut des Sciences de la Vigne et du Vin, noted that many wines show these very same aromatic components, leading to aromas of coffee, toasted bread, roasted hazelnuts, etc.
The presence of these components raised a big question. The Maillard reaction usually takes place at temperatures over 150 degrees Celsius (300 degrees Fahrenheit) and in dry conditions. So how could it take place in a liquid that normally doesn’t reach above 30 or 35 degrees Celsius (90-95 degrees Fahrenheit)?
The key, Marchand realized, is that the reaction takes place in two steps. The first one converts sugars into related compounds called carbonyls, which then react with other components like peptides or amino acids to form the heterocyclic compounds. In wine, the carbonyls are by-products of fermentation, in particular malolactic fermentation, meaning that the necessary precursors are present in the wine for the second step of the reaction to take place. Over time, the Maillard reaction becomes part of the complex set of chemical processes that help develop the highly desirable aging bouquet of fine old wines.
Indeed, as a paper by Ana Maria Monforte of the Universidade Católica Portuguesa in Oporto pointed out, when it comes to heterocycles, “there is a connection between Maillard reaction and oxidation [with regards to] molecule formation during Port ageing.” In her study, the formation of one particular heterocyclic compound, sotolon (which provides maderized aromas and notes of curry), was connected to factors like temperature and exposure to oxygen, with more oxidative contexts like barrel aging leading to higher amounts of sotolon forming over a given period of time, compared to the low oxygen context of a bottle.
More generally, the exact relation between the formation of Maillard-related heterocycles and oxygen in wine remains unclear, with many types of reactions taking place. But Stéphanie Marchand has also seen in experiments with different fermentation vessels that oxygen seems to have an influence on which precursors and components emerge. Finding out more about those mechanisms could be considerably interesting to winemakers. This could help them figure out how to manage their wines in the early stages of production, in order to encourage the production of a complex and desirable bouquet – for pairing with steaks or any other food, or just for aromatic enjoyment.