Some compounds contribute positively, initially. But, if there is too much, they quickly become faults. Ethyl acetate (C5H8O2) is an example of such a compound. In low quantities, it can contribute to the aroma of a cider but in large quantities, it becomes a fault. It will turn the positive sweet and fruity aroma into a chemical or solvent smell or sometimes a vinegary one. Many will attribute the aroma with nail polish or acetone. This usually happens at levels above 200mg/l(1).
Ethyl acetate is created during fermentation by yeast and like many compounds each yeast strain will produce different amounts. This can be defined by a ratio of ethanol to ethyl acetate. This is because the yeast with either follow a pathway that produces ethanol or another the produces ethyl acetate. The other way ethyl acetate is produced is from lactic or acetic acid bacteria. The bacteria processes ethanol and acetic acid into ethyl acetate.
Oxygen plays a big role in the creation of ethyl acetate. Excessive oxygen during fermentation can create larger amounts of acetic acid. This puts the cider at higher risk during aging. Oxygen during aging either from excessive headspace or from racking and processing can also create more ethyl acetate. Besides oxygen, aging on lees can increase the risk of ethyl acetate production. This is because the yeast autolysis process releases nutrients and reactionary compounds that support the creation of aroma compounds, which ethyl acetate is one.
The most effective way address ethyl acetate is prevention. Selecting yeast strains that are low producers as well as avoiding oxygen are your two best methods. You can also use sulfites to kill bacteria that might produce the ethyl acetate during aging and avoiding aging on the less. Just remember that adding sulfites can also have negative impacts and aging on lees, especially fine lees, can have positive impacts. Most decisions are a trade off but two good rules for home cider makers are to 1) practice good sanitation of your equipment and 2) avoid oxygen once fermentation starts. There are always exceptions but these will help minimize cider faults.
(1) Carlos de la Roza and associates, Ethanol and ethyl acetate production during the cider fermentation from laboratory to industrial scale, Process Biochemistry 38, 1451-1456, 2003
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