Diacetyl is a naturally occurring aroma compound that can give wine a buttery, creamy or butterscotch-like character. It is most closely associated with malolactic fermentation, during which lactic acid bacteria metabolise citric acid and other compounds and may produce diacetyl. Its concentration depends on bacterial activity, oxygen exposure, lees contact, sulphur dioxide and cellar management.
During malolactic fermentation, bacteria such as Oenococcus oeni convert malic acid into lactic acid. Diacetyl can be produced as part of related metabolic pathways. Some diacetyl may be reduced or consumed by bacteria or yeast, so the final amount depends on when the wine is separated from the lees and how the process is managed.
At low levels, diacetyl can contribute subtle buttery or creamy complexity. At higher levels, it may dominate the wine with aromas of butter, butterscotch or cultured dairy. Whether this is desirable depends on the wine style and the balance with fruit, acidity and oak.
Example: a Chardonnay that has undergone malolactic fermentation and lees ageing may show buttery aromas, while a crisp, high-acid Chablis made without MLF generally shows much less obvious diacetyl character.
Buttery aromas are often associated with diacetyl, while vanilla, toast and spice may come from oak. Brioche and bread-like notes may develop through lees ageing and autolysis. These characteristics can overlap in a finished wine but have different origins.
Chef’s note: diacetyl is not automatically a fault. A moderate buttery note can suit rich seafood, poultry and cream sauces, while an excessive buttery character may overwhelm a delicate dish.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
