Diaectyl Rest-High Gravity Ale

[lsteffens]

I've read a lot about the necessity of a diacetyl rest for lagers before crash cooling. Is it necessary to do a diacetyl rest on a high gravity ale? I brewed an Imperial Pale Ale that has been fermenting steadily for nine days at 68 degrees. The fermentation has slowed considerably in the last two days. Do I need to raise the temperature for a few days or just leave it alone? Thanks.

[TheDarkSide]

This isn't Willem, is it?

Shat the Producer has been a big proponent of raising the temps late in the fermentation...something he picked up from a brewer. ( Sorry details are a little fuzzy, as am I ). I think it's tell give the yeast a kick to help clean up some of the junk they left behind.

[NMWildAles]

Yeah, I always raise my temps a few degrees toward the end of fermentation also. I, too, picked this tip up from a commercial brewer.

[ajdelange]

Diacetyl is produced after fermentation by non-enzymatic oxidation of acetolactic acid. The only practical way to get rid of it is to expose the beer to active yeast which will reduce it (enzymatically) to less flavorfull acetoin and unlimately butane diol. Adding active yeast (kreusening) of course does this as doesraising the temperature to kick the remaining yeast into high gear one last time and traditional (slow) lagering does it as well as long as it is done over live yeast. Traditionally lagered beers do not require a diacetyl rest and ales, in which more diacetyl is tolerable, usually don't either. It is when you are trying to rush lagering, as commercial enterprises must do to save on capital equipment and labor costs, that diacetyl rests and/or kreusening are necessary. This all assumes that the acetolactate is produced by yeast and not spoilage organisms in which case it's pretty much a lost cause.

[ApresSkiBrewer]

+1 on ajdelange's take.

You should be fine without bumping the temperature, as long as you don't rack/cool the beer too soon/unnecessarily. Taste it. If you aren't picking up Diacetyl, don't sweat it.

That being said, I almost always bump my fermentations a few degrees towards the end to finish them out.