Ester Aromas & Flavors in Wine
Ester Aromas & Flavors in Wine
Wines can exhibit a number of wonderful aromas and flavors that result from tiny quantities of chemical compounds created in the grape growing or winemaking processes. Modern science has greatly improved our understanding of the chemical or biological processes that create these aroma and flavor compounds, and essentially all of them found in wine have been identified and categorized through advanced analytical capability. This Carl’s Corner was influenced by two informative articles (1,2) and focuses on the role that a special group of compounds, known as esters, play in both winemaking and our enjoyment of wine.
Esters are compounds that create aromas and flavors common to fruits, like bananas, strawberries, pineapple, raspberries, cherries, and even citrusy and floral notes. Only a few esters are generated in grapes as they ripen, while most are created via chemical and biological reactions during fermentation. Modern analytical techniques have been able to identify over 160 different esters in wine, but most of these exist at concentration levels below the human sensory threshold.
Esters are some of the most volatile and fleeting aroma compounds found in wine, characteristics that are both interesting and perplexing. Once formed during fermentation, they tend to be unstable, either disappearing via evaporation or further chemical reactions. So, it is common that fruity characteristics esters bring to a wine are short-lived, and often dissipate within months or just a year or so after bottling. This, as you might expect, is part of the aging process that changes the aroma perceptions of older wines.
On the surface, chemical reactions that form esters are not too difficult to appreciate. However, a full understanding of the chemistry can get very complex. The simple explanation is that esters are formed when alcohols, including ethanol, the primary alcohol created by fermentation of grape sugars, react with organic acid molecules that are either native in the grapes or created during fermentation. Simple, right? Don’t worry about the chemistry, just keep reading.
The subject of yeast selection is an important one among winemakers as certain aromatic yeasts tend to form lots of esters while other neutral yeasts do not. If the winemaker chooses to focus on a bright and fruity wine style, of course aromatic yeasts are preferred. However, if a different style is preferred, say one that focuses on other longer-lived aroma and flavor compounds, like terpenes, thiols, pyrazines, and norisoprenoids that actually originate in grapes, then a neutral yeast will be preferred.
The temperature of fermentation is another important factor in creating and maintaining esters and their fruity characteristics. Cooler fermentation will keep evaporation to a minimum, and many winemakers believe more esters are formed at lower temperature. However, recent research suggests that there are a range of esters formed at different temperatures, and that even with greater evaporation rates, more of them may survive in the wine during marginally warmer fermentations. (3)
Combining the impacts of both yeast selection and fermentation temperature, myriad combinations of esters can result. Classic low temperature fermentation (50’s) produces tropical fruit esters, higher temperature fermentation (70’s) gives more floral esters, and in-between temps (60’s) give a combination. It should be noted that esters can interact with each other to change the aromas one perceives to something entirely different than the aromas of the individual esters. (3)
Some common esters, especially in white or rosé wines, are listed below. Recognize that ethanol is the dominant alcohol in wine, and acetic acid (vinegar), the oxidation product of ethanol, is the most common acid in wine.
Ester Alcohol Acid Aroma
ethyl acetate ethanol acetic see note below
Note: The most prominent ester in wine; at low concentrations can be perceived as
desirable and fruity; at higher concentrations can impart a solvent or nail polish remover
aroma, and, ultimately the pickled, vinegary aroma associated with volatile acid spoilage.
Isobutyl acetate isobutyl acetic ripe apple
isoamyl acetate isoamyl acetic banana, strawberry
ethyl hexanoate ethanol hexanoic green apple, anise
ethyl octanoate ethanol octanoic ripe fruit, beer
ethyl decanoate ethanol decanoic floral, ripe fruit
ethyl lactate ethanol lactic milky, buttery
produced during malolactic transformation of malic acid into lactic acid
The impact that esters have on the early enjoyment of rosé wines is not something we typically think about, but when one encounters a “tired” rosé that is too far beyond the vintage, the lack of aroma and flavor can be a signal that esters originally in the wine have “moved on.” This is why most folks recommend drinking rosé wines within a year or so of the vintage date.
The business of understanding all the important wine aroma compounds, including esters from fermentation, and terpenes, thiols, pyrazines, and norisoprenoids from the grapes themselves, is really Ph.D. research-type stuff. However, for most wine-drinkers, appreciation of these wonderful compounds should only require a glass of wine and a bit of time to enjoy drinking it.
1) https://daily.sevenfifty.com/the-science-of-esters-in-wine/ by Alex Russan, based in Santa Barbara County, CA, owner-winemaker of Metrick wines and Alexander Jules and a company through which he imports Sherry and other Spanish wines. He writes about and teaches enology, viticulture, and wine tasting.
2) https://www.wineland.co.za/esters-wines-own-perfume/Esters – wine’s own perfume by Edo Heyns, a South African winemaker, researcher, and writer, Mar 1, 2014
3) Research by Michael Jones, fermentation specialist for the well-known yeast purveyor Scott Labs in Petaluma, CA.