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) <ref name="Roos_2018" />. Many other aromatic and flavor compounds can be produced in varying amounts by ''Brettanomyces'' (see [[Brettanomyces#Secondary_Metabolites|''Brettanomyces'' secondary metabolites]]).