Caprylic Acid, the common name for octanoic acid, a medium-chain saturated fatty acid. Caprylic acid has an unpleasant, fatty, oily, rancid aroma; like caproic acid, it is excreted by yeast during adverse conditions.
The corresponding ethyl ester, ethyl caprylate (also known as ethyl octanoate), contributes to beer aroma and flavor and can be described as fruity, floral, banana-like, pineapple-like, or even brandy-like in its pure state. It tends to go hand in hand with development of a yeasty flavor that may or may not be desirable, depending on the concentrations and the style of beer.