Attenuation Threshold

[wyatttho]

Hey, so I'm sure this question has been asked many times before, but is there a good value of attenuation to determine when to rack from primary to secondary? I've got a stout that's been in primary for seven days now, OG of 1.069, and when I took a hydrometer reading today it weighed in at 1.027, which (I believe) comes out to about 61% apparent attenuation. There's little to no activity in the airlock anymore, and the gravity still seems a tad high, but this would probably also slightly go down in secondary too. If attenuation is a quantitative measurement that tells how much of your sugars have been fermented, is there a threshold percentage that kind of signals the OK to rack? For example, in one thread I read something about waiting until over 70% of your sugar has been attenuated, but then again attenuation can be affected by numerous other factors (oxygenation, pitching rate, temperature...), so I'm just not totally sure whether it's okay for me to rack or not.

Any advice would be much appreciated, and thanks!!

 

[Captain Damage]

IF you go to secondary, you should wait until fermentation is done and you've reached your terminal gravity. Many of us here, however - myself included - now advocate never racking your beer to secondary. The only reason I rack to secondary now is when I'm adding fruit. I even dry hop in the primary. You will get better beer if you just leave it undisturbed for a few weeks. That means not opening it up for a bunch of gravity readings.

What is usually referred to as a "secondary fermenter" is really what commercial brewers call a "bright tank," as little or no actual fermentation is going on there. Commercial brewers move their beers to bright tanks to free up their fermentation vessels while the beer lagers and some of the particulates drop out so their filters don't clog up prematurely. A fermenter that is not fermenting beer is costing the brewer money. On the homebrew scale, transferring beer to secondary is an opportunity for oxidation and contamination to wreck your beer. Leaving it in primary for a few weeks (most of us do 3 or 4 weeks, then bottle) will allow most of the particulates to drop out and give the yeast time to clean up some off-flavors.

The exceptions are if you're racking onto fruit, in which case the secondary actually is a secondary fermentation vessel, and beers that require extended aging such as barley wines.