Changes

Aging hops leads to oxidation of acids and oils. Generally, brewers seek to avoid this to preserve the aromatic and bittering properties of their hops by freezing them and storing them in vacuum sealed packaging (oxygen exposure is by far the larger factor for hop degradation, followed by ambient room temperatures, which is significant because hops are often not stored in vacuum sealed packaging). However, some beer styles, including lambic and historical styles, make extensive use of aged hops. Aged hops still retain some antimicrobial properties and can be used for microbial inhibition. In addition to their antimicrobial activity, aged hops contribute important flavor and aroma compounds and precursors to beer. These flavor descriptors often include herbal, tea-like, Earth-like, and a more dull bitterness. [[Isovaleric Acid]] might also contribute to the complexity to of a beer that has been brewed with aged hops (although the presence of isovaleric acid in aged hops is considered temporary, and will eventually age out of hops that are aged). Historically, some brewers had issues keeping mildew from growing on aged hops that are aged in higher humidity areas (sulfur was used to combat mildew, which often gave beer a sulfur, rotten egg aroma) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1228610483833830/ Conversation with Ron Smith and Aaron Barker on historical storage of hops. 02/07/2016.]</ref>.