Diacetyl Question

gruntingfrog · Jun 5, 2006

MrGoodbeer.com has an aroma troubleshooting section ( http://www.mrgoodbeer.com/aroma.shtml ) that I was reading today, and I have something that needs clarification. On the "butter" smell, it says that it is produced by diacetyl, and that...

Higher fermentation temperatures decrease the level of diacetyl.

I thought that higher fermentation temperatures increased the level of diacetyl.

Anybody?

magno · Jun 5, 2006

According to Brew Chem 101 by Lee W. Janson, diacetyl can be increased by:
Worts with high amounts of sugars and starches
Worts low in the amino acid valine which promotes proper reduction of diacetyl
Decresed floccuation and settling of yeast by weak yeasr strains and/or premature wort cooling
Defective yeast prodiced by spontaneous mutatuins that have lost their ability to reduce diacetyl
abbreviated fermentation - yeast initially produce diacetyl, but at later stages of fermentation promote its reduction (short fermentation wont allow completion of the diacetyl reducing stage)
Excess oxygen in the wort, which causes diacetyl prosuction by alternative reaction pathways

By the same book, diacetyl can be decreased by:
Good wort recipes that provide yeast cells with all essential nutrients
Healthy strong yeast cells with good floccuation and sedimenting charicteristics
Warmer fermentation temperatures which increase yeast metabolism, including diacetyl reduction. Although easy for ales, lager temperature may also be raised to 68*F for the last 24 to 48 hours of primary fermentation.

The book also says that diacetyl can come from a bacterial contamination.

Hope this cleared things up (cause it took ages to type out

)

- magno

Kaiser · Jun 6, 2006

gruntingfrog said:
Higher fermentation temperatures decrease the level of diacetyl.

I thought that higher fermentation temperatures increased the level of diacetyl.

Higher fermentation temperatures in the early phases of the fermentation (after pitching the yeast) may lead to a higher diacetyl level. But since the yeast also converts the diacetyl into less nasty stuff, once it is running out of sugar, a raise in temperature towards the end of the fermentation speeds up the yeast's metabolisim and its uptake of diacetyl. It would also take up the diacetyl if the temperature is not raised. This process would just take longer.

Kai