Converting the ethyl acetate defect back to ethanol
We are a producer of fruit liqueurs and fruit spirits, and ethyl acetate is a principal ester and flavor component. This ester is produced by the slow esterification reaction of acetic acid and ethanol produced during fermentations at low pHs. It is always present when we ferment strawberries and apples. At low concentrations, ethyl acetate imparts fruity notes, and at higher concentrations, an undesirable glue-like smell. Fortunately in humans, we metabolize ethyl acetate back to ethanol and acetic acid by hydrolysis from esterases.
Ethyl acetate can be an insidious little ester to remove in its pure form, because its boiling point is very close to ethanol. In the craft distiller’s world we are not working with pure substances, thankfully! Ethyl acetate forms positive azeotropes with ethanol as well as ethanol and water, which reduce its boiling point and make the separation a bit easier.
We really don’t want the ethyl acetate, so rather than distilling it off, why not convert it into something useful? Indeed, that is ethanol!
If we end up with a heads or hearts fraction with too much ethyl acetate present, there is a simple way to reprocess this back to ethanol. We add a cheap and plentiful strong base, sodium hydroxide (NaOH), to the fraction and let it sit for a few weeks. The saponification reaction with the carboxylic acid ester and the strong base gives us sodium acetate and ethanol, back to our target molecule!
But, we have our ethanol now sitting in a solution of sodium hydroxide and sodium acetate! The solution is usually develops a pale yellow color over time. This is still acceptable, because the ethanol and the hydroxide now form an ethoxide in solution. As long as water is present, the equilibrium is favored to the alcohol, not the ethoxide. If we completely dried this solution, we could obtain the sodium ethoxide, but we don’t need to go this far.
The alcoholic lye solution is simply distilled using a short path distillation apparatus to remove the ethanol and water to the volume we want. The sodium acetate solution is discarded. WARNING – THIS MUST BE DONE IN GLASS! This solution is a strong base and will ruin your copper or metal still pots.
