Important products of hop aging are the C4 and C5 isomers of short chain fatty acids; namely 2-methyl propionic acid (isobutyric acid). 2-methyl butyric acid and 3-methyl butyric acid (isovaleric acid). These acids are sensory active and moreover. after the esterification during beer production they can provide further sensory active compounds contributing to a stale aftertaste. https://www.lorenametaute.com/