As beer ferments, there are changes that you can see as time goes on. If you have a clear fermentation container, the liquid changes color, and solids start dropping to the bottom. If you can only observe the top of the liquid, you should at least see the krausen start to dissipate as the yeast does its work. But what if the yeast isn’t doing its work?
If your beer isn’t fermenting properly (or taking longer than usual), you might have a stuck fermentation. This happens when the yeast is unable to convert sugar to alcohol properly. To get your yeast colony back up and running at full speed, you’ll need to confirm the yeast is stuck, check the temperature, give it oxygen, and add nutrients.
Read on to learn how you can tell if your fermentation is stuck and how to reset your homebrew.
Topics We Cover
Is It Stuck?
Before you starting trying to restart your fermentation, you need to confirm if it is actually stuck.
To check your fermentation rate, you’ll need to take a hydrometer reading and compare it to the original gravity reading (OG) and the expected final gravity (FG).
Not sure how to use a hydrometer? I’ve got detailed directions in this article.
If the second measurement isn’t at your FG but lower than your OG, give the batch some more time (12-24 hours) and take another reading. If this last reading is the same as your previous one, you’ve confirmed that your fermentation is stuck.
However, if your numbers are still dropping (just slowly), double-check the yeast characteristics. Some yeast strains like the Saison Duponts are notorious for stalling.
Temperature
Probably the most important factor in maintaining yeast health is temperature. It starts with making sure that the wort is at the ideal temperature during the pitching process. Too early (hot) or too late (cold), and the yeast can be killed off or go dormant.
During the fermentation phase, the temperature needs to be kept within the ideal range. Most homebrewers are familiar with the kettle thermometer that clips on the side of the container. This is a handy tool but try and get readings at different locations instead of clipping it to the same spot.
An alternative is a digital infrared thermometer, which will give you a reading without touching the liquid. This reduces the risk of contamination; however, some brewers have reported problems when recipes call for grain mash. The foaming can cause issues with getting a reading.
When coming up with a solution to regulate the temperature of your fermentation container, always remember that yeast activity generates heat! Depending on the strain, it can cause an additional 5 to 10 degrees of warmth on top of the ambient temperature. Always be aware of the difference between the two and understand that the liquid temperature is the vital reading.
Solutions range from cheap (cool or cold room) to expensive (fermentation chamber). Some brewers have even reported success with surrounding the container in water and adding ice or cold blocks as needed.
If you’ve determined that the ambient temperature range was previously too cool for your yeast, you may want to swirl the container lightly. It’s possible that the yeast became dormant, and going back into suspension with the correct temperature will get them going again.
Oxygen
If you’ve somehow missed the step of aerating your wort before putting it in the fermenter, then the yeast can stop reproducing as it eats up all the oxygen in the liquid.
The solution is to introduce oxygen into the liquid by swirling it or taking a sterilized stirrer and agitating the mixture.
Be warned that some argue that you should never reintroduce oxygen once you start fermenting. The only solution that Precision Fermentation recommends is to add wort with a known good and vibrant yeast culture (krausening).
Nutrients
Your recipe may call for adjuncts like corn or rice that are not easily processed by yeast, even though they have been gelatinized by cooking in water to form a mash. Supplements may be necessary for the yeast to ferment properly.
Generally, supplements come in ammonium phosphate-based nitrogen supplements and are easily bought at most brewing suppliers. There are also specially tailored supplements like White Labs Servomyces, which corrects a specific mineral deficiency in the liquid.
Before deciding to go with a specific treatment involving nutrients, make sure they are compatible with the yeast strain used in your batch!
Prevention
An ounce of prevention is worth a pound of cure…or, in this case, healthy yeast. By now, you should have figured out that keeping your yeast happy and healthy is the key to avoiding stuck fermentation.
You can prevent future problems with your yeast by using a starter, ensuring you pitch at the optimal temperature, pitch enough yeast, and take regular gravity readings.
Use Yeast Starter
You can think of a yeast starter as a micro-batch of beer whose sole purpose is to make more yeast!
Pitching a large amount of healthy and vibrant yeast is a sure way to make sure that there are enough organisms to convert all the sugar into alcohol.
But let’s say you’ve harvested yeast from a previous batch, and you want to make sure it’s still viable. Use that yeast to create a starter, and you can be sure that they are still healthy and active before pitching.
Just make sure you keep the pitch rate for your type of yeast in mind.
Pitch At The Optimal Yeast Temp
Yeast is usually stored at cold temperatures, but they need warm temperatures to activate and start feeding. The transition between the two must be managed carefully, even though the term “pitch” suggests you can just throw it in there.
When creating your wort, you have to know what temperature is required for your strain of yeast.
You want to make sure that the liquid has gotten to the optimal range for the yeast before you add it in.
Pitch Enough Yeast
Understanding the pitch rate for the type of yeast you are using is another way to ensure your fermentation doesn’t get stuck. Not introducing enough yeast into the wort (called underpitching) can also lead to undesired results even if the fermentation eventually completes.
Worse, the yeast can completely stall out, leaving you with something that’s not quite a wort but not yet beer.
So if underpitching is a thing, can you overpitch?
Generally no…but maybe.
There are guidelines for standard pitch rates that will fit a general flavor profile like ale or lager. If you decide to go with a higher rate, you will come out with a cleaner flavor as the yeast doesn’t reproduce.
But some brewers prefer to go below the standard rates to coax out more flavor from the yeast. Most do so knowing the risks involved with not having enough yeast.
Take More Gravity Readings
Many brewers start out measuring their original gravity (OG) and then wait until whatever time period their recipe says to start checking final gravity (FG).
If you take the time to take measurements, say roughly every 12 hours until FG, you can feel for how long a batch should take in the fermentation container.
If the next batch isn’t dropping at the same rate (given the same recipe), you’ll have plenty of time to start figuring out what might have gone wrong.
