Esters

Esters are compounds resulting from the reaction between acids and alcohol in wine. This esterification takes place during the alcoholic fermentation of grapes and during aging. It is the neutral, odoriferous esters that give wine its pleasant, light odor, described as a young, fruity aroma.

Wine, esterification, esters

An ester is a carboxylic acid derivative, obtained either from a monobasic acid or from a polybasic acid according to the following reaction:

    acid + wine alcohol = ester + water.
This esterification process can take place :
  • during alcoholic fermentation (transformation of grape sugars into alcohol), known as enzymatic esterification,
  • during wine ageing, known as chemical esterification..
To date, oenologists have identified over a hundred esters, present in varying concentrations in wine. They are classified into two main categories according to their properties, and therefore their impact on organoleptic character and quality.
  • Neutral esters, which are volatile and odoriferous, contribute to the wine's aromatic profile.. They are produced from monoacids or polyacids, mainly by enzymatic esterification.
  • Acid esters, which are fixed and non-odorous, contribute in small part to a wine's acidity, but not to its aromas. Ils sont produits uniquement par estérification chimique et à partir de polyacides.
After fermentation and aging, the levels of neutral and acid esters are similar. But when we look at the links between esters and aromas, whether in red, white or rosé wines, it's the former that interests us!

Focus on neutral esters in wine and their effect on oenology

The aromatic profile of a wine appears in a precise order :

  • primary aromas, known as varietal aromas, linked to the grape's color (red or white) and, more specifically, to the grape variety,
  • secondary aromas, derived from alcoholic and malolactic fermentation,
  • tertiary aromas, which appear as the wine ages and are known as the "aromatic bouquet".
Neutral esters therefore contribute to a vintage's secondary and tertiary aromas, with a wide variety of young, fruity notes that are both delicate and complex. This aromatic contribution varies according to the type of neutral ester.

Neutral ester type Esterification substrates Flavours
Ethyl esters of fatty acids (EEAS) Short-chain fatty acid + ethanol Light red fruit, freshness of young wines
Higher alcohol acetates (HAA) Acetic acid + higher alcohol* Higher notes of fresh fruit (pear, banana, English candy, etc.)Floral notes (rose, etc.)

Neutral ester type Ethyl esters of fatty acids (EEAS)
Esterification substrates Short-chain fatty acid + ethanol
Flavours Light red fruit, freshness of young wines

Neutral ester type Higher alcohol acetates (HAA)
Esterification substrates Acetic acid + higher alcohol*
Flavours Higher notes of fresh fruit (pear, banana, English candy, etc.)Floral notes (rose, etc.)

*wine alcohols with a higher number of carbon molecules than ethanol

The evolution of a neutral ester in wine

The aromatic ester content of a wine inevitably decreases over the years. On the one hand, the neutral esters produced during aging are present in smaller quantities than those produced during fermentation. What's more, their production remains slow. On the other hand, esterification, which is reversible, eventually gives way to the opposite phenomenon: hydrolysis (reaction of esters with water). Nevertheless, certain parameters enable the winemaker to optimize ester production in his wines:

  • slow, regular alcoholic and malolactic fermentation,
  • maintaining a low temperature during vinification,
  • the use of yeast strains and lactic acid bacteria (such as Œnococcus œni) whose enzymatic activity favors esterification,
  • must clarification, to remove molecules responsible for lower ester concentration.