Expert: Spencer W Thomas - 9/14/2007

Question
I just started my first batch of home brewed beer.  It has been fermenting for a week (started 9-07-07) when do I know when the beer is done, the type is a pale American ale. Thank you for your response

Answer
If it's been fermenting for a week, it is probably finished, unless you had it in a cold place.  Is it in a fermenter with an air lock / bubbler?  If so, it's done when bubbles are less than one per minute.  

If you're really not sure, maybe it's in the basement where it's a bit cool, you can siphon out some into a beer bottle, stick an airlock on the beer bottle, and put it in a warm place (above the fridge is usually good).  If fermentation starts back up and goes actively for a while, then it's probably not finished.  This is called a "forced fermentation test."

Do you have a hydrometer?  It can be a handy tool for determining how much your beer has fermented so far.  An American pale ale should have had a starting measurement on the hydrometer ("gravity)") of about 1.050, and should finish around 1.015 or lower, but the real key is to watch the gravity as it ferments.  It'll be done when the gravity doesn't drop any further for 24 hours.

If you do go in to take a sample for a forced fermentation test or to measure with a hydrometer, be sure to sanitize anything that will touch the beer in the fermenter.  Don't put the sample back in the fermenter.  It's not worth the risk of infection to save a few ounces of beer.

Another test, although less useful to a beginning brewer (because of lack of experience -- but you have to start sometime!), is to taste the beer.  (Again, anything that goes into the fermenter to get the sample to taste must be sanitized.)  Finished beer will taste a little sweeter than expected, because there is no carbonation, and because it's flat will not be as flavorful as your finished, carbonated beer.  If it tastes really sweet, it's not done.  If it's only a little bit sweet, it probably is done.

Finally, if it's not quite finished, and you bottle it anyway, it will continue to ferment in the bottles.  What this means is that as the beer ages, it will get more and more carbonated.  In the extreme case, bottles could "explode" (it's usually not that dramatic, but you do end up with beer leaking out).  But if you're drinking the beer steadily, you'll have warning.  Before it gets carbonated enough to break the bottles, it'll start "gushing" -- when you open the bottle, it will foam up and out by itself.  This is your warning that you should drink it up quickly and/or put the rest of the bottles into the fridge to stop any further fermentation.  

I was recently cleaning out my "brew closet" and found four bottles of beer that was brewed in 1992.  The beer within was pretty sweet, and did foam up a bit when I opened it.  It was clearly underfermented, but it lasted 15 years without causing a problem.