Recently Barbara wrote in with this question on a possible stuck fermentation:
How can I tell if my wine is stuck and not fermenting in the secondary fermenter? Should the airlock be bubbling?
-Barbara
Matt’s Answer:
Hi Barbara,
Thank you for reaching out with your question! Being able to identify a stuck fermentation is an important skill to have and can keep you from taking drastic measures when you might not need to.
The latter days of a fermentation are going to be much slow.er than primary fermentation. It is certainly possible to get a stuck fermentation at this late stage of the process given that sugar supplies are running out and alcohol levels are getting higher. This makes life hard for the yeast.
As such you may only see a bubbles in your airlock every few minutes as things wind down. Using your airlock to gauge fermentation activity is a good idea but you need to check on it periodically to make sure it is still seated properly and that the water levels are correct. If either of these is off the carbon dioxide being produced may be essentially going around the airlock.
This brings us to determining whether or not you have a stuck fermentation on your hands or not.
How to Tell if You Have a Stuck Fermentation
The easiest way to tell if a wine is stuck is to first taste the wine. If the wine tastes even a little bit sweet you know that there’s sugar left in your wine. As this is what the yeast convert into alcohol, fermentation should not end until all the sugar is gone. If your wine is not sweet then fermentation is likely over.
You can also look at your current specific gravity reading. A reading of 0.998 or less indicates the wine is likely dry as well. So by tasting and testing you can get a good idea of where you are in the fermentation process.
If your wine is sweet then grab your hydrometer, take a specific gravity reading, and record your results. Then wait one week and take another specific gravity reading.
If:
- the second reading is lower than the first reading fermentation is still going (sugar is being consumed).
- the two readings are the same (and the wine tasted sweet) then you probably have a stuck fermentation (sugar is not being consumed).
- the second reading is higher than the first reading then something went wrong (sugar is being created? that’s not possible). Double check your current reading and wait another week to take the next reading. Disregard the first one.
It can be quite difficult to recover from a stuck fermentation, especially if it gets stuck with very little sugar left in the wine. This is a topic we’ll cover soon here at the Academy.
Cheers Barbara!
-Matt Williams
Additional Information
Photography by: Tim Patterson
Greetings! New winemaker here. Have 4 gallons in second fermentation. Testing specific gravity with trial beaker and hydrometer. Question: Can I put the test sample back in the carboy?
Hey Rancho, most sources say not to, however, I do all the time. I’m very careful about sanitation and keeping the sample from getting mixed with anything that hasn’t been sanitized.
On small one gallon batches you just can’t afford to toss a test jar worth of wine every time you test. Because of that I got into the habit of being very careful when I test and returning the sample to the carboy. So far, no problems.