Diacetyl

From Beer

Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone (two C=O groups, side-by-side) with the molecular formula C₄H₆O₂. Diacetyl occurs naturally in alcoholic beverages and is added to some foods to impart a buttery flavor.

[edit] In alcoholic beverages

At low levels in alcoholic beverages, it contributes a slipperiness to the feel of the beer or wine in the mouth. As levels increase, it imparts a buttery or butterscotch flavor (butterscotch itself may be devoid of diacetyl).

It is produced during fermentation as a byproduct of valine synthesis. During this synthesis yeast produces α-acetolactate, which escapes the cell and is spontaneously decarboxylated into diacetyl. The yeast then absorbs the diacetyl, and reduces the ketone groups to form acetoin and 2,3-butanediol, relatively flavorless compounds.

Beer sometimes undergoes a diacetyl rest, which entails elevating temperature slightly for two or three days after fermentation is complete, to allow the yeast to absorb the diacetyl it produced earlier in the fermentation cycle.

This page uses content from Wikipedia. The original article was at Diacetyl. The list of authors can be seen in the page history. As with Beer, the text of Wikipedia is available under the GNU Free Documentation License.