The Beginner Brewer: Fixing Things: A Stuck Fermentation

Tuesday, 29 October 2013

Fixing Things: A Stuck Fermentation

Sometime, despite our best efforts to be kind to beer, it's not kind to us. If you brew beer, you will (I promise) come up against some of the more vexing issues that plague brewers the world over. In the next few weeks, I'll be covering some tactics you can employ to help your homebrew along when things go awry.

A Stuck Fermentation

It makes cold shivers of terror flow through the spines of most brewers: a fermentation that. Just. Stops. 

You’ve measured your fermenting beer as instructed , and for some reason, the SG refuses to dip below 1.020 (Of course we’re assuming that you’re not brewing a monster beer with a OG of more than 1.080, in which case it may not ever go below 1.020). 

Also, remember to give things time—beer can take up to a week to complete primary fermentation, and for big beers, this can be even longer.

But assuming that it’s a week down the line and you’re not brewing the world’s strongest beer, then yep, you’re in 1.020 limbo hell. Sorry. But is all lost? Not necessarily. It’s time to apply some emergency procedures. Here are some moves to make:

Step 1. Check your measurements.


It may seem obvious, but perhaps there is nothing wrong with your fermentation. You may have just measured wrong.  Of course, if you haven’t measured at all, and you think that you've got a stuck fermentation because there is no more bubbling coming from the airlock—shame on you. You HAVE TO measure your gravity! Eyeballing the airlock is not a recognised scientific measure of fermentation activity. Ever.
You may have gotten the math wrong..

If you used a hydrometer, measure the temperature of the wort and compare it with the temperature the hydrometer is calibrated to (that will usually appear along the side of the hydrometer itself). If there’s a difference between wort temperature and hydrometer temperature, you may need to adjust the reading (I don’t need to remind you to take sanitary precautions, right?). Click here for a handy calculator that can help with that.

If you’re using a refractometer, measure again—sometimes you don’t have enough liquid on the face plate. Then adjust the reading for fermenting wort. You can do this in Beersmith, or click here for a handy calculator. If you’re measurement is still correct after this, it’s time to move on to..

Step 2. Check the fermentation temperature.


Since you’ve checked the wort temperature in Step 1, you should now know what the fermentation temperature is. For ales, it should be around 16-23 C. For lagers, it should be around 14-17 C. 

Chilly temperatures: Yeast doesn't like that.
One common cause for a stuck fermentation is too chilly an ambient temperature. The yeast will then go back into a state of suspended animation and drop out to the bottom of the fermenter.

If this is your problem, there’s a relatively easy solution—heat up the fermenter by putting it in a warmer room in your house, or wrap an electric blanky around the fermenter—but be careful—you don’t want to overheat the brew: that can cause additional problems down the line.



Step 3. Shake your money-maker.


Yeast. It likes to go to sleep (sometimes).
 No—not your booty (although, then again…). If your temperature is fine, it might just be that you’ve started with old or tired yeast. 

What is needed is to “rouse” the yeast from its slumber at the bottom of that fermenter. Gently (and I mean gently) shake the fermenter a bit to put some yeast back into suspension. You can repeat a few times per hour for 2-3 hours if you like. Just don’t shake so violently that you introduce oxygen into your beer—that will be a BAD THING, and will make the finished beer taste like cardboard.

Once you've shaken the fermenter, let it rest and measure again after a couple of days to see if there’s a difference

Step 4. More yeast. 


If you’ve gone through all the preceding maneuvers and things are still not looking up, then it’s time to break out the final, last ditch, we’re-not-kidding-anymore solution: re-pitching yeast. 

Make sure that you’re pitching fresh, viable yeast. For dry yeast, just pitch another packet. For liquid yeast, pour the vial directly into the fermenter. Wait a few days. Pray to the big beer pixie in the sky. And then measure again.

If you've faithfully followed all the steps in this toolkit and there’s still no change, it may be time to throw in the bar towel. I know it sucks. But you’ll just have to dump the batch, go over your brew notes, and try to figure out what went wrong. 

Here are some likely suspects:

  • Old yeast: expired yeast ain’t going to get you far
  • Under-pitching yeast: for dry yeasts, this is seldom a problem, but for liquid yeasts, it could be. Check out this link to calculate your correct pitching rate.
  • Yeast shock: pitching yeast into wort that is more than 10C colder than the yeast itself is a bad idea and can cause yeast shock, and in turn, yeast slumber.
  • Pitching at too high a temp. Yeast is resilient, but it won’t survive you pitching it into wort that is hotter than 40-50C.
  • Sanitation. Often, when brewers follow poor sanitary practices, yeast can be outperformed by bacteria. This can cause a stuck fermentation, and incredibly bad tasting beer.

Next time, I'll be tackling the thorny issue of hazy homebrew. Click here for the next installment of fixing things.

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{Picture Credits: Equations by Robert Scarth; Ponds on the Ocean by NASA Goddard Space Flight Centre; Sleep by Agus Munoraharjo; }

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