Stuck Fermentation

What causes a stuck fermentation

Have you ever had a beer or wine fermenting well, then slow down or stop altogether before finishing? Chances are you may have a sluggish or stuck fermentation; that is, a fermentation that has stopped before all the sugar is transformed into alcohol. It needs to be coaxed back into action so you can get on with your brew. Just remember, though, this is the exception and not the rule.

Since this may happen to many of us at some point in time, I thought it might be helpful to understand some of the reasons why this could happen, plus some help on preventing and correcting this situation. Before getting into these causes and cures, make sure you actually do have a stuck fermentation. To determine this you need a hydrometer. A hydrometer is a very important part of the home brewing process. It lets you follow your brew from start to finish. It tells you what is going on at certain stages and tells you when to bottle. When taking the hydrometer reading, make sure to use a considerably larger diameter testing tube than your hydrometer or the carbon dioxide bubbles could actually raise the hydrometer in the testing jar and give you a false reading. Also, check out other possibilities of what might be happening. Just because there isn’t much activity in your airlock doesn’t necessarily mean a stuck fermentation. For example, if you are using an airlock on your primary fermenter, the gasket may be leaking and a bit of carbon dioxide gas is escaping. If you are brewing in hot weather or a hot area, especially beer, your brew may actually be finished in a couple of days. After you have eliminated these false alarms, it looks like your yeast has lost its appetite, leaving you with a sluggish or stuck fermentation

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Why might this happen?

It could be the rise in alcohol content, which causes the yeast cells to die and stop the fermentation. Often, there is excess carbon dioxide and a lack of oxygen.
The yeast may be ill; that is, if you left sterilizing solution in your fermenter, the yeast could be ruined. On the other hand, if you didn’t sterilize or sterilize well, wild yeasts and bacteria can take over. In this case, there is no cure.
Sometimes yeast can go dormant if they fall below a certain temperature. Also, if the temperature is too high, it can weaken the yeast.
Your brew may be lacking in something the yeast needs to do its work. For example, oxygen- insufficient oxygen in your brew when you pitch the yeast could result in a sluggish fermentation. But remember, when fermentation is underway, avoid adding any more oxygen, as it is harmful to your brew at this point.
Some yeast strains may be lacking in nutrients required to do the job. This sometimes happens especially in fruit wines, as too much sugar may inhibit the yeast.

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How to avoid a stuck fermentation

Keep your equipment sterilized. Everything that comes into contact with your brew should be sterilized well.
Watch the fermentation temperature. Use a thermometer to check the temperature often. Try to maintain the required temperature range and be careful of drafts.
Aerate your wort or must by stirring or shaking approximately ten minutes before pitching the yeast, to introduce as much “free oxygen” as possible.
Also consider using a yeast nutrient or yeast energizer to help the yeast work more effectively. It is like adding a multi vitamin. Yeast nutrient is a mixture of substances intended to help the yeast do its job properly during fermentation. It is generally unnecessary for home brewing, but some people, especially when brewing beer, like to add it along with the yeast to give it a little extra boost. Yeast energizer is also a nutrient, but contains ingredients not found in the yeast nutrient. It is useful in making wines of higher alcohol content (over 14%) and to try restarting a stuck fermentation once in the secondary.

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How to fix a stuck fermentation

Once you have eliminated other things and you know you do indeed have s stuck fermentation, there are solutions. Start with the easier ones.
Warm your brew up a few degrees either by raising the room temperature or use a heat belt around the fermenter (or other variations you may have developed to warm it up). At the same time, occasionally stir gently for the first three or four days that fermentation is being reactivated. (Make sure you sterilize your spoon.)
Rouse the yeast by shaking the carboy. Sometimes frequent rousing of the yeast will be all that is needed.
Try adding some yeast energizer to see if it will restart the fermentation.
If the specific gravity is still quite high when it sticks, maybe pitching another yeast will do the trick; however, if there is already a high presence of alcohol, it is doubtful this will work. You will need to prepare a yeast starter outside the brew and introduce it back into the carboy as follows: Take one-half liter of your brew and one-half liter of water and put in a gallon jug under an air lock. Pitch a yeast and a pinch of yeast energizer. Leave 24 hours at room temperature. Double the volume each day from the carboy until the gallon jug is full. It will probably take a week to get going. After the week and it is fermenting well in the gallon jug, introduce it back into the carboy. This should do the trick and your brew will be back on track.

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