How to Beat the Stuck Fermentation Monster


"Until at last, I threw down my enemy and smote his ruin upon the mountainside."

-Gandalf the White

You've brewed the perfect wort.  You bullseyed your strike temp, you had a most excellent cold break, your OG was right on the money and you used nothing but the finest combination of ingredients that you know will score you first place in the National Homebrew Competition.  You've only got one problem: Your fermentation has prematurely ground to a halt. Terror sets in. You did everything right- how could this be happening? You don't want to be stuck with a cloyingly sweet, half-fermented, malty, cavity-causing sugar drink, so what do you do?  Fear not. That gold medal may find its way around your neck yet.  

First and foremost, it's important to verify that you do indeed have a stuck fermentation before you go into panic mode. Yeast can be tricky little fungi and might appear to have punched out early, at least to the disrobed eye, but they may still very well be fermenting away, albeit at a slower, less visible pace.  Remember, just because your fermentation isn't barreling along like a '67 Shelby Mustang GT500 on the drag strip (yes, I had to google "best muscle car" for that reference- you're welcome, Steve McQueen), doesn't mean you've got a stuck ferment.  Not to mention, you may not see any bubbling action from your airlock if the lid on your fermentation bucket isn't completely sealed, or if there are any cracks in your fermentation bucket or in your plastic airlock, or if the airlock isn't forming an air-tight seal where it's connected to your fermentation vessel (carboy or plastic bucket).

Even though observing the bubble frequency from the airlock on your fermenter is a good cursory way to check the pulse of your fermentation,  it's no substitute for doing a gravity check. Now's the time to break out ye olde hydrometer, take a reading and if your gravity is within a few points of your target, take a breath- you're the brave little survivor of a false alarm.  The yeasties probably just went to town and devoured the wort turbo-style while your back was turned.  On the other hand, if it's been at least a week from when you originally pitched the yeast and your gravity is off by quite a bit, say 5 or more points, you'll want to jot down the gravity reading, give it a few days, and take another check to see if the gravity has dropped any.  If it has, then chillax, the yeast are still on the job, so stop being such a slave driver and give Django a break--- they'll gets it done when they feels like it, bossman.

It should also be mentioned that it behooves you to ensure that you are reading your hydrometer correctly and that it's working properly.  When reading your hydrometer, make sure to account for the temperature of your reading with respect to whatever temperature the hydrometer is calibrated to (usually 60°F/15.56°C), which you should be able to see in small print on the scale inside the glass of the hydrometer. Generally speaking, if you're taking a reading at room temperature, the temperature adjustment is small, typically about one point, so it's probably not worth the effort of calculating the adjustment.  Though a malfunctioning hydrometer is rare, if you're questioning it's accuracy, you can test it by taking a sample of some distilled water cooled to the temperature to which your hydrometer is calibrated.  If you get any other reading than 1.000, it's probably time to pick up a new hydrometer.

So you've done a gravity check, you're hydrometer is in working order, you've waited a few days, come back and there's still no drop in gravity? Then you, my friend, may be the latest victim of a full-blown stuck fermentation.  First of all, don't feel inadequate- this happens to the best of us (wink).  Heck, even the exceptional Garret Oliver of the renowned Brooklyn Brewery recounts a story of an ethical conundrum he faced when encountering a stuck fermentation close-call in the book Beer and Philosophy: The Unexamined Beer Isn't Worth Drinking.  He went through the same sense of angsty helplessness you might be feeling and was left with the hard choice of what-to-do.  Before I tell you what he did (and didn't do), let's make a quick diagnosis of the potential cause of your dilemma.  

Stuck fermentations are usually the result of under-pitching yeast, pitching unhealthy yeast, or improper fermentation temperatures.  No matter what the cause, your yeast have decided they don't like their labor conditions and have officially gone on strike. However, the most common culprit in the case of the stuck fermentation is under-pitching.  Under-pitching, or not adding enough yeast to properly ferment your beer, is usually a problem that stems from either too much wort (quantity), too little yeast, or too strong a wort (high gravity), too little yeast.  The preventative measure employed by most brewers is either to buy a sufficient amount of yeast to properly ferment the batch-size or starting gravity, or to grow an appropriate yeast starter.  In other words, try not to look too shocked when fermentation stops ahead of schedule if you're using only a single vial of yeast (which is usually designed to ferment a 5 gallon batch) to ferment your 10 gallon batch of super-high gravity Barleywine.  

The next possible suspect is unhealthy yeast. Though more uncommon today with the ready availability of fresh, properly stored yeast, unhealthy yeast can cause your ferment to sputter out unexpectedly.  If you're purchasing yeast from your local homebrew shop, make sure to check the 'best used by' date on the package, especially for liquid yeast, and it should go without saying that liquid yeast should be kept cool and stored in a refrigerator prior to use.  If you're using yeast that you've washed (saved) from a previous brew or harvested from a bottle, make sure to grow an appropriate starter to ensure the yeasts viability.  In the past, I've used liquid yeast that I've harvested and stored in my frige for over a year and have had good results, but believe me I had an extra vial of liquid yeast handy as a back-up. [Want to know more about how to become a yeast farmer? Then check out our article on How to Harvest and Grow Yeast from a Beer Bottle.] 

Last but not least, keep an eye on your fermentation and pitching temperatures. All yeast have their own fermentation sweet-spot temperature range, but let your ferment temp drift too low (depending on the particular yeast strain), and you may inadvertently cause your yeast to go into hibernation mode. On the other side, if you pitch your yeast to hot wort (110°F/43.33°C or higher), you may have accidentally killed off a good portion of the yeast cells, if not the entire culture.  Assuming the yeast does pull through it's trip to the sauna, pitching too warm can potentially create certain off-flavors in your beer like fusel alcohols, for example--- think rubbing alcohol.  On my first batch of beer, I novicely pitched dry yeast to a wort that was at least 100°F (37.78°C). I was lucky that the beer survived virtually unscathed, but I certainly don't take my chances today.   

I know- shoulda, coulda, woulda.  All those preventative measures are great, but you've got a stuck ferment now and your beer needs your help, so let's talk about how to rescue your beer from the potentially cloyingly sweet malt juice you've got now. 

First off, you may know that aggressively shaking your wort in order to aerate it just prior to or upon pitching your yeast is a good practice because it adds oxygen to the beer and helps your yeast get started and grow.  While this is true, it is the last time you want to intentionally add oxygen to your beer during the fermentation process.  In other words, giving the fermentor a vigorous shake after fermentation has already begun may not only lead to oxidizing your beer which can lead to shelf-life problems and cardboard flavors in your beer, it would also be considered yeast abuse- that's a class 6 felony and punishable by flogging while listening to Flogging Molly.   

Let's take a look below at a few ways you can unstuck your fermentation, going in order from most passive/laissez faire to the more hands-on options: 

1. The Wait and See Approach: This is the first option not only because it requires the least amount of effort, but also because it's the most natural, least invasive, and, given enough time, will almost always work.  Fermentation is sometimes a stubborn wonder of nature, especially with high gravity beers or finicky yeast strains like Saison or Ringwood, and sometimes fermentation can take weeks longer than expected.  Even under the perfect conditions, just remember, yeast is working on it's own schedule, so have a homebrew and some faith, and let the yeast do its thing. 

2. Rockabye Baby: Try giving the fermentor a really slow, "gentle rock". No splashing and no bubble-making as you want to avoid oxidation. Hold one hand to steady the fermentor at the bottom of the bucket or carboy, and use the other hand to gently sway the beer back and forth a few times (not more than 5 or 6). The idea is to lovingly rouse the sweet little baby yeast from the bottom of the fermentor, giving them a gentle sway to coax them to get the job done. 

3. Some Like it Warm: In combination with the "Rockabye Baby" approach, consider raising your ferment temperature up a bit. Yeast tend to become more active at warmer (not hot) temperatures.  Of course every beer has a certain flavor profile to shoot for, and that profile in very large part depends on your fermentation temperature and schedule, but if you've got a stuck ferment, then it's worth possibly taking it above that ideal range if it means getting your beer back on track.  For example, if you're fermenting at 62°F (16.67°C), raise it to 68°F (20°C).  To avoid off-flavors, be careful not to push the temp too much above that particular yeast's ideal fermentation temp because you might not appreciate the fusels or fruity esters lurking on the warm side of the Force.

4. Call in the Reserves: You can pitch some additional healthy yeast to help finish the job.  I'd stick with the same, or similar, type of yeast you started with, or use a more attenuative, clean yeast (a yeast that contributes no real additional aroma or flavor profile); consider, say, a California Ale yeast or an American Hefeweizen yeast before going with a super high-gravity Champagne-style yeast which can make your beer drier than Happy Hour at a Mosque.  It wouldn't hurt to make a starter with the new yeast either. By the wayeven though larger strains can metabolize longer starch chains like melibiose thereby further lowering the final gravity of a beer by a very small percentage, the attenuation limits of lager and ale strains do not differ in any significant way.

5. Energize: Some brewers have had success kicking their fermentation back into gear by adding a small amount of yeast energizer to their stuck ferment.  Most homebrew stores will sell the product which is usually a blend of diammonium phosphate, magnesium sulfate, yeast hulls and vitamin B complex.  Luckily, I've never had to use yeast energizer, but it's an option to keep in your back pocket. 

6. Chemical Warfare: Some brewers use artificial enzymes to reactivate or increase the speed of fermentation in their beer. When time is money, I can understand the temptation, however whenever possible, try keeping your beer pure and natural and stay away from the Agent Orange.

7. Blend-O-Matic/Beano-Matic: It's rare, but sometimes when all grain brewing, it's possible that your mash temps got too high (162+°F/ 72.22+°C), which can result in the increased production of unfermentable sugars. In other words, even though you might hit your final mash gravity spot on, a significant portion of the sugar making up that gravity may be unfermentable. So when fermenting with said wort, your final gravity may come in higher than planned, in which case you would need to test (via a forced fermentation) whether the apparent stuck fermentation is due to the yeast stalling out, or simply the amount of unfermentable sugars in the beer. A forced fermentation test can be done by pulling a sample of your beer and placing it in a container you can fit an airlock on; before securing the airlock, add a Beano tablet to it (yes, that Beano), and after a few days, check for visual signs of fermentation, or do a gravity check to see if the beer has dropped in gravity. 

The idea is that Beano contains the enzyme amyloglucosidase, which converts most unfermentable sugars into fermentable ones so that the yeast can consume them. If the Beano enables fermentation to continue, then your problem was due to an abundance of unfermentable sugars.  At this point, you can add a few tablets of Beano to your beer to kick-start fermentation, but be warned: Beano can and most likely will ferment your beer down to a final gravity below 1.000, in other words, bone dry. This also means you need to allow fermentation to completely stop, otherwise you may be risking bottle bombs if you're bottling. Also, keep in mind that the extra converted sugar in your Beano-beer will result in a higher final ABV, albeit a lower calorie beer. Alternatively, if your forced fermentation test reveals an excess of unfermentable sugars and you don't want to add Beano to your batch thereby creating a bone-dry Beano-beer, consider brewing another batch with a lower final gravity in order to blend it with the beer with the higher final gravity.     

Well, there you have it.  So the next time you're paid a visit by the ever-lurking shadow of the stuck fermentation monster, you’re now armed with a few more tricks to help you stare down one of the feared boogie men of brewing.  Oh, by the way, when the nasty head of the stuck fermentation beast (in the form of a fussy little saison, naturally) reared its ugly head in front of Garret Oliver, brewmaster extraordinaire, and after he'd exhausted all the tricks in his book, he was tempted with the choice of adding an artificial, lab manufactured, yeast-steroid cure-all enzyme to the beer to get it going again. That choice was becoming more and more appealing as time went on and the pressure to produce mounted, but Garret stayed strong and sure enough after some time and additional yeast, the brew finished out and went on to win multiple awards.  The moral of the story?  Well, aside from keeping it real-ale, I guess it's the same moral from so many a brewing tale- RDWHAHB (Relax. Don't worry.  Have a homebrew). 




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