Cleaning up at fridge temps?

[worlddivides]

This is just something I've wondered about recently. My understanding has always been that after fermentation is over, you give yeast a few days at regular fermentation temperature to "clean up," which is mainly reabsorbing diacetyl, though I know there are some other minor things yeast does in its cleanup process. But recently I've seen tons of posts mentioning that yeast can "clean up" in the keg or in the bottle at fridge temps. On the one hand, I know this has to be true for lager yeasts, since although they typically ferment between 40 to 55F (5C to 13C), they lager at close to freezing (32F / 0C), and during this lager time they clean up diacetyl (albeit VERY slowly, hence the diacetyl rest commonly used). But I find it more believable that a lager yeast that can ferment at 5C can have some amount of activity at 0C. But how can an ale yeast that ferments at 16C to 30C clean up diacetyl and other compounds at, say, 3C or 4C? Or is this statement I've seen posted in tons of places on both this forum and other homebrewing forums false?

Personally I normally keg 10-14 days after brew day, sometimes longer than that for styles that need more time and sometimes shorter than that for styles like IPAs and pale ales that are best drunk young, but I know some people keg 5-7 days after fermentation, and this has me wondering.

 

[JohnSand]

I almost always ferment three weeks, or at least until the beer clears.

 

[Bobby_M]

I wouldn't count on it. By the time you're in the packaging, you already have a tiny portion of the yeast colony left.

 

[worlddivides]

I wouldn't count on it. By the time you're in the packaging, you already have a tiny portion of the yeast colony left.

Agreed. It just makes me wonder why so many people say it. Even if there was enough yeast left to handle it, how could ale yeast even be active at such low temperatures? If you keg an incomplete fermentation and keep it in the fridge, that should essentially stop the fermentation there. The buildup of CO2 would be dangerous if the keg was returned to room temperatures where fermentation could restart, but I know some people add fruit to the keg without pasteurizing and immediately transfer to fridge temps. So I just can't wrap my head around how it could be, say, 20 degrees or more below the lower end of fermentation temps but the yeast is somehow still capable to "clean up" (reabsorb diacetyl, etc.).

 

[corncob]

Most yeast stains taste bad. I think it's easy to confuse flavor improvement due to yeast activity and flavor improvement due to yeast settling out completely, especially for newer brewers. The latter happens fast at fridge temps with ale yeast. The former probably stops completely when you drop below about 60deg with most ale stains. I don't know for sure because I time packaging based on taste. Even when I run an English from an open fermenter into a cask pretty soon compared to when fermenting closed, the conditioning is a couple more weeks of slow activity well above fridge temps.

I'm not the most sophisticated brewer (by a wide margin compared to many on the forums here) and I keep finding reasons to recommend keg conditioning for those of us who don't have it all together. It really covers a multitude of sins. Add a spunding valve, it's almost impossible to not make good beer.

 

[mac_1103]

Yeast - ale, lager, other - don't die at refrigerator temps and they don't become completely dormant either. But metabolism does slow down pretty drastically. So if you're waiting for them to metabolize any unwanted compounds in your beer at 40F or below, you're going to have to wait a very long time.