Diacetyl is a natural by-product of fermentation. It is most commonly recognized as a butterscotch or buttered popcorn flavor in the beer. Perceptible diacetyl is considered a fault in most beer styles, especially in lagers. If you pitch your yeast to a warm wort, then drop the temperature to within the recommended range for fermentation, you may have some undesirable diacetyl characteristics in your lager. To eliminate any diacetyl that may be present after primary fermentation, raise the temperature of your beer to 55-60°F for 24-48 hours before lagering. This re-energizes the yeast and allows them to eat up the diacetyl before slowing down once again during lagering.

Lager Brewing