The sour effect in many wild ales is usually a combination of lactic, malic, and acetic acids produced by the bacteria lactobacillus and pediococcus. Historically it has been common to measure a beer’s acidity by its ph; the lower the ph, the more acidic the beer. The problem is, ph doesn’t indicate acidity strength or sour flavor reliably. Ph simply reports the ratio of hydrogen (H+) ions to hydroxide ions (OH-) within a solution. Much in the way IBUs fail to accurately describe bitterness with relation to the balance of body and sweetness, ph fails to describe how sour a beer will taste. Fortunately for us all, the mad scientists at Firestone Barrelworks have been developing a system that describes the acidic nature of wild ales in terms of titratable acidity or “T.A.” Because this method of measuring acidity actually describes how much acid is in a beer, it is a much more accurate description of how sour a beer can be predicted to taste.
Brendan Megowan, “Wild Style”, Beer Paper LA (July 2016), 19.