Science
Esters and fermentation fruit
The compounds behind banana, pear-drop and tropical notes in young wine — made by yeast, and short-lived.
The short answer
Esters are formed by yeast during fermentation and account for much of the fruity character of young wine. They are chemically unstable, and their concentration falls over the first few years in bottle, which is why young wines smell fruitier than old ones.
Overview
Esters are a large family, and several dozen are present in wine at perceptible levels.
They are the clearest case of aroma that came from the winery rather than the vineyard, which makes them a useful corrective to the assumption that everything in a glass reflects a place.
How it works
The mechanism, at the scope it has actually been established.
Yeast synthesise esters from alcohols and acyl-CoA compounds during fermentation, as a by-product of lipid metabolism.
Ester production is strongly influenced by fermentation conditions. Cooler temperatures are associated with higher retention, as is limited oxygen and adequate but not excessive nitrogen, which is why aromatic whites are commonly fermented cool.
Yeast strain matters considerably; commercial strains are selected in part on ester profile.
Esters hydrolyse slowly back towards their constituent acids and alcohols in the acidic conditions of wine, so their concentration declines over the first years in bottle. Some esters associated with aged wine form slowly by the reverse route.
Individual esters are associated with broad descriptors — isoamyl acetate with banana and pear drop, ethyl hexanoate with green apple and aniseed — though no single ester accounts for a descriptor on its own.
Why it matters in the glass
It is the mechanism behind "drink young". A wine bought for its fruit will not have the same fruit in five years.
It also explains the pear-drop character of carbonic-maceration Beaujolais, and why Prosecco and cool-fermented Sauvignon Blanc are made the way they are.
Compounds named on this page
Where a compound comes from is chemistry; what it smells like is perception. These are kept apart deliberately.
- Esters
- Fermentation-derived compounds responsible for much of the fruitiness in young wine. Associated with banana, pear drop, green apple, strawberry, tropical fruit. Caution: No single ester accounts for a descriptor. Attributing "banana" to isoamyl acetate is a shorthand, not an identification.
Sources
Sources consulted
- The Australian Wine Research Institute — AWRI
- UC Davis Department of Viticulture and Enology — University of California, Davis
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