Butterscotch and rancid butter flavors in beer are caused by:

Butterscotch and rancid butter flavors in beer are caused by:

• A. Lactic acid
• B. DMS
• C. Ethyl acetate
• D. Diacetyl

Answer: (D)

Butterscotch and rancid butter flavors come from diacetyl, a buttery, off-dry note that yeast can produce during fermentation. Diacetyl forms as a byproduct of metabolism and is normally reduced by healthy, active yeast later in fermentation to less assertive compounds, but if the yeast isn’t able to finish, the diacetyl remains and you taste those buttery, sometimes rotten-butter-like flavors. This is distinct from lactic acid, which causes sourness; DMS, which gives a cooked corn aroma; and ethyl acetate, which adds a solvent-like fruity note. So the buttery, butterscotch character points to diacetyl.

Butterscotch and rancid butter flavors come from diacetyl, a buttery, off-dry note that yeast can produce during fermentation. Diacetyl forms as a byproduct of metabolism and is normally reduced by healthy, active yeast later in fermentation to less assertive compounds, but if the yeast isn’t able to finish, the diacetyl remains and you taste those buttery, sometimes rotten-butter-like flavors. This is distinct from lactic acid, which causes sourness; DMS, which gives a cooked corn aroma; and ethyl acetate, which adds a solvent-like fruity note. So the buttery, butterscotch character points to diacetyl.