What is that “buttery” character?
Diacetyl is the chemical responsible for the buttery character found in white wines that undergo MLF. Diacetyl is formed as a by-product of the catabolism of pyruvate, which is often derived after MLF from citric acid sources. Citrate and oxygen concentration will increase diacetyl levels while living yeast cells and SO2 levels in the wine will reduce concentrations. The ML strain used will also have an effect based on its catabolism of citric acid. Thus, there are multiple factors to think about when addressing the “butter issue”. The initial state of the wine, winemaking method (for example sur lies) and choice of bacteria strain all must be considered.
