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**Netflyer** · 04-04-2010, 11:50 AM

Ok, in my continuous travels of 'not knowing sh$^' I thought diacetyl was formed if the fermentation got too hot, depending on the yeast of course but there was a point 72F-78F where if the fermentation remained over that temp. for x amount of time (or did it just need to once hit those temps?) that diacetly was formed. (wow - long sentence sorry)

So, in 'Brewing Classic Styles' (Zainesheff, Palmer) directions are given to ferment (this is a stout - using Wyeast Irish Ale Yeast) at 65 degrees and 'slowly raise the temperature during the final third of fermentation by 6 degrees to reduce the diacetyl levels in the beer' ...

So I'm confused. I thought they weren't forming at 65, and then raising the temp to 71 if anything would form, and not destroy them? Are they just always there and an intermediate temp like 71 gets rid of them? Pretty weird, cause then if you go too high they reform??

One more thing... what would you consider the last third of fermentation? Hours 36+ ? My typical strong fermentation is 48-72 hours depending upon the wort.

Thanks for any help people!

**Bobby_M** · 04-04-2010, 12:53 PM

Diacytel is a natural byproduct of fermentation and the reason to raise the temp towards the end is to encourage the yeast to stay active enough to process this off flavor. For an ale, it's at about day 5-7 and for a lager it's day 10-12. Of course, YMMV.

**eager_brewer** · 04-04-2010, 01:26 PM

For me depending on the beer, I will raise the temperature almost 10 degrees during the final stage. This has helped me not have butter beer. I had a batch one that tasted like you were drinking a stick of butter. YUCK. I usually raise the temp for 24-36 hours. However most of mine are big beers so your time may vary. :-)

homebrewer_99 · 04-04-2010, 01:38 PM

I got the big D once in a Speed Brew. All I did was take the keg out of the keezer, added 1/4 pack of yeast then let it re-ferment at room temps and it was gone in a week.

It's my understanding that it's caused when you rack too soon and the yeasts haven't cleaned up after their party in the primary.

***Yooper*** · 04-04-2010, 01:40 PM

I agree. Also, some yeast are notorious diacetyl producers while some yeast strains are not. So, if you've got a yeast strain that is noted to produce lots of diacetyl, a diacteyl rest would be a great idea for that beer.

**eager_brewer** · 04-04-2010, 01:42 PM

You don't happen to ahve a list of these guys do you??

menschmaschine · 04-04-2010, 01:47 PM

Yeast produce diacetyl during fermentation. Then when the food supply (sugars) begin to run out, they start to metabolize things they've produced earlier in fermentation, like diacetyl. Raising the temp later in fermentation "encourages" yeast to do this. If the temp is raised too early, it will produce more diacetyl than it would have and the yeast may not clean it all up, leaving some in your beer.

homebrewer_99 · 04-04-2010, 01:58 PM

Quote:

Originally Posted by menschmaschine

...produce more diacetyl than it would have and the yeast may not clean it all up, leaving some in your beer.

...which can be partially, and sometimes totally, covered up by dry hopping...

**Netflyer** · 04-04-2010, 09:48 PM

Cool guys and gals, thanks for the responses... I've personally only had 'butter' beer when I let the temp get too high... I'm always around 63-68 but I think the yeasts I've chosen have pretty decent attenuation so therefore didn't need the rise at the end. The yeast I'm using in this case is Wyeat 1084 and that has 73% attenuation. Compare that to 1028 which has 75% attenuation or 1968 (my fav) which has 69% and it doesn't seem that low... Meanwhile, these directions were for a stout and the notes on Wyeast 1084 are 'Dry Diacetyl, fruity flavor char. of stouts'... so seems desireable to some degree in stouts anyhow.

Pick · 04-07-2010, 02:36 PM

I've got a batch in a fermenter that spent 2 weeks under normal fermentation temps. Last week was a little higher, should I worry?