The Oxford Companion to Beer definition of
Ferulic Acid is a phenolic acid found in cellulosic cell walls and in the cell walls of the starchy endosperms of cereals, including wheat and barley.
It is covalently attached to polysaccharides in these walls and is released by the action of an enzyme called feruloyl esterase. Ferulic acid is an antioxidant and has attracted much attention for its potential health benefits, including a possible role in countering cancer. It is a substrate for the enzyme ferulic acid decarboxylase, which converts ferulate into 4-vinyl guaiacol, with its distinctive clove-like aroma. See 4-vinyl guaiacol. This enzyme is present in the ale yeasts that are used in the production of weizenbiers, and the clove-like note is an index of authenticity. However, the enzyme is also elaborated by wild yeasts, e. g., Saccharomyces diastaticus, meaning that a clove or spicy note in beers other than weizenbiers tends to be an indicator of wild yeast contamination. Ferulic acid is also used extensively in industry, for example as the precursor of a vanilla substitute.
Ou, S, Kwok, K.-C. Ferulic acid: Pharmaceutical functions, preparation and applications in foods. Journal of the Science of Food and Agriculture, 84 (2004): 1261–1269.