Changes

Spontaneously fermented beers are usually characterized by the compounds produced by the complex and highly variable fermentation profile explained above. This generally includes the production of [[Lactic Acid|lactic acid]] by lactic acid bacteria and [[Acetic Acid|acetic acid]] by acetic acid bacteria and ''Brettanomyces'', which lend a sour and fruity flavor to the beer. ''Brettanomyces'' is responsible for many of the volatile aroma compounds, including [[Tetrahydropyridine|tetrahydropyridine]] (also produced by lactic acid bacteria), phenols such as 4-ethylguaiacol (smokey, spicy, clove) and 4-ethylphenol (barnyard, horsey, spicy, smokey, medicinal, Band-Aid), and esters such as ethyl acetate (pineapple in low concentrations, nail polish in high concentrations), ethyl lactate (fruity, creamy, rum-like), ethyl caproate (fruity/aniseed), ethyl caprylate (fruity with creamy mushroom and cognac notes), and phenylethyl acetate (sweet honey and rose-like). ''Brettanomyces'' can also produce volatile fatty acids such as [[Isovaleric Acid|isovaleric acid]] <ref name="Roos_2018" />. Some strains of ''Brettanomyces'' are also known to release the enzyme beta-glucosidase to break down glycosides, which can result in the release of flavor compounds. This enzyme is also responsible for allow ''Brettanomyces'' to consume cellobiose (wood from barrels). However, Daenen et al. (2007) found that none of the ''B. bruxellensis '' strains isolated from lambic could utilize cellobiose, but strains of ''B. anomalus '' and ''B. custersianus '' isolated from lambic could utilize cellobiose, indicating that not all ''Brettanomyces '' strains (especially ''B. brucellensisbruxellensis'') can break down glycosides or use cellobiose in wood as a food source (see [[Brettanomyces#Glycosides_and_Beta-Glucosidase_Activity|beta-glucosidase activity]] for more information). See the [[Brettanomyces#Secondary_Metabolites|''Brettanomyces'' secondary metabolites]] page for a complete list of flavor compounds that ''Brettanomyces'' can produce.