Changes

Some volatile esters that give the beer a fruity flavor, such as isoamyl acetate that gives the beer a banana flavor, can decrease to levels below their flavor thresholds over time in packaged beer. other Other volatile esters such as ethyl 3-methyl-butyrate (contributes a wine-like character), ethyl 2-methyl-butyrate (contributes a wine-like character), ethyl 2-methyl-propionate, ethyl nicotinate, diethyl succinate, ethyl lactate, ethyl phenylacetate, ethyl formate, ethyl furoate and ethyl cinnamate (fruity, sweet character) are formed during beer aging. Lactones, which are cyclic esters, such as the peach-like hexalactone and nonalactone tend to increase during beer storage and have a significant impact on the flavor of aged beer <ref name="Vanderhaegen_2006" />. While most ester formation and hydrolysis (breakdown) in beer during aging are mostly acid-catalysed, some of this activity is due to esterase enzymes. It has been shown that some esterases are released by yeast autolysis during beer aging. This release of esterase enzymes is strain dependent, with ale yeast having more potential for this activity than lager yeast. The enzyme is most active at 15-20°C and is destroyed by pasteurization.