By definition, a stuck fermentation is a fermentation that has stopped before all the available sugar in the beer has been converted to alcohol and CO2. If the bubbles in your airlock slow down before your beer has reached its final gravity, you may have a stuck fermentation. Were you to give up on the beer at this point, it would taste semi-sweet and pretty bad. Not to worry, there are ways to fix this. Before we get into how to fix it, let’s make sure that you have a stuck fermentation.
Here are a couple of ways to check:
Fortunately, stuck fermentations are pretty rare. But when they do happen, it’s important to make corrections right away and get the fermentation going again for optimum results.
Try the following tips to get that airlock bubbling again:
Simply move the fermenter to an area that is room temperature, or 68-70 °F. In most cases, too low a temperature is the cause of a stuck fermentation, and bringing the temp up is enough to get it going again.
Open up the fermenter, and rouse the yeast by stirring it with a sanitized spoon. Sometimes putting the yeast back in suspension will get it going again.
Add some yeast energizer to the beer. Add 1/2 teaspoon per gallon of beer, and stir well. NOTE: While it may seem like a good idea, Midwest does NOT recommend adding yeast nutrient at this point. This may result in leftover vitamins that can stimulate spoilage microbes.
If none of these tips get the fermentation going again, you can pitch a yeast starter. This is called krausening. If you have space, you should make a 2-quart (2-L) starter for a 5-gallon (19-L) batch. If you do not have the space in your fermenter, a 1-quart (1-L) starter will usually work too, but a larger number of active yeast cells is better. Normally for a starter you would decant the liquor before pitching the sediment to the wort. You can do that here but since you want to add the yeast at full krausen it is preferable to add all the liquid in the new starter.
- Take 4 oz. (113 g) of dried malt extract (DME), and add water to a total of 1 quart (1 L), and stir until the DME is dissolved.
- Add a pinch of yeast nutrient and boil the solution for 20 minutes, then top up with water as necessary and cool to about 70 °F (21 °C). You can also skip the boiling portion and just use our Fast Pitch canned wort.
- Aerate thoroughly (oxygenation is better) and pitch with a fresh yeast sample; if you have a stir plate keep the pitched wort continuously agitated.
- Maintain at room temperature until it is fermenting vigorously (the so-called high krausen stage), then add this starter to the beer.
- For best results the beer should have been left in the fermenter during this time so that much of the dissolved CO2 will have escaped.