A few years ago, I wrote an article on old wines vs. new wines. In it, I talked about how the aromas, flavors and colors change as wine ages. Today, the focus will be on oxidation, reduction, polymerization, and esterification. What are these terms? Well, according to Wiens Cellars, these are the primary reactions that occur during wine aging.
How Does Oxidation Contribute to Wine Aging
Wine Enthsiast tells us that “Oxidation happens when a wine’s exposure to air triggers a series of chemical reactions that convert ethanol (what we commonly refer to as alcohol) into acetaldehyde.
“Open-tank fermentation, pumping over, racking and bâttonage (lees stirring) are all processes that introduce oxygen into a wine. There’s also oxidative aging, which includes any wine that’s spent time in a porous vessel like a wood barrel or clay amphora. Bottle aging under cork, which is also porous, is another controlled way to transform wine with oxygen over time.”
What Is Reduction’s Role in Wine Aging
Reduction is the opposite of oxidation. It’s when wine is made with limited exposure to air. In reduction, sulfur dioxide is often added as a preservative to help maintain an equilibrium by preventing excessive oxidation. It also contributes to the formation of sulfur-containing compounds that impact wine aroma. Reduction refers to the gain of electrons, while oxidation is the loss of electrons. According to Wine Anorak, these processes often “occur in tandem, in what are called redox reactions. And oxygen doesn’t have to be involved for oxidation to occur: oxidation is the process of loss of electrons, and other chemical entities can do a similar job to oxygen, which has lent its name to the process.”
WineEnthusiast explains that “Reductive winemaking usually takes place in hermetic steel tanks, and it’s used for many white wines, as well as some reds. A popular form of this technique is carbonic maceration, in which the tank is flooded with inert carbon dioxide gas. The process blocks contact with oxygen while whole grape clusters ferment. This method may be best known to wine lovers in the production of Beaujolais Nouveau, and is known to produce particularly fruity aromas.”
Polymerization’s Role
Vintage Cellars highlights the role that polymerization (sometimes called tannin polymerization) plays in aging wine: “As a wine ages, its tannins slowly undergo polymerization, a reaction that binds them together in long chains. Once bound together, tannins fall to the bottom of the bottle as sediment, lose their ability to bind with other compounds, and the aged wine loses its astringent qualities and starts to taste mellower.”
This process contributes to the development of a wine’s texture and structure.
Esterification’s Role
Esters are responsible for many fruity and floral aromas in wine. Esters are created when the alcohol in wine reacts with the acids. This process is called esterification. Vintage Cellars tells us that “hydrogen, which is more abundant in wines with greater acidity, encourages this reaction to take place. Paradoxically, the presence of hydrogen can also make the reaction reverse, turning esters into alcohol and acid… This complex reaction is one of the ways in which wine could be called a living, breathing organism: the give-and-take between esters and their primary compounds means that the flavors in wine are constantly changing.”
