What You Need to Know
During primary fermentation, maltose and maltotriose are converted by Brettanomyces spp. and Lactobacillus/Pediococcus spp. into ethanol, CO₂, lactic acid, and acetic acid. Secondary aging further metabolizes these acids, lowering pH and generating phenolic compounds such as 4‑ethylphenol and 4‑ethylguaiacol that give the beer its characteristic barnyard aroma.
The Science
Primary Reaction
Spontaneous fermentation of malt sugars by wild yeasts and lactic‑acid bacteria producing ethanol, CO₂, lactic acid, and acetic acid