How To Stop A Wine Fermentation

I have several 2 1/2 gallon jugs of wine going at this time started in December. The problem is – I am satisfied with the taste and the alcohol content however they won’t stop working. It seems like in the past, when I have allowed the wine to stop fermenting on its own, the taste changes? I have read that potassium sorbate does not completely kill off the yeast? What can I do to stop the ferment at this time and how much alcohol (brandy?) would I have to add to stop the ferment. Thanks.

Name: Skip K.
State: MN
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Hello Skip,

The first thing I’d like to point out is that stopping a wine fermentation is not normal. What is normal is letting the wine fermentation continue until all the sugars in the wine must have been consumed by the wine yeast. If you prefer your homemade wines sweet, you would add sugar to taste at bottling time, and then add potassium sorbate to eliminate a chance of re-fermentation in the wine bottle.

What also is not normal is having a wine fermentation continue on for months. A typical wine fermentation will last anywhere from 5 days to two weeks. The fact that yours has lasted for months tells me that there is something fundamentally wrong.

I would suggest taking a look at the Top 10 Reasons For Fermentation Failure that is listed on our website. It runs through the most common reasons for a wine fermentation to either fail to start or to drag out, such as the case with yours. See if any of the top 10 reasons ring true to your situation. Now on to your question…

What can I do to stop a wine fermentation?
Well, what you can’t do is use either sulfites such as Campden tablets or use stabilizers such as potassium sorbate. Neither of these will stop a wine fermentation with any dependable success. Here’s why:

• Sulfites (Campden tablets, sodium metabisulfite, potassium metabisulfite):
  Wine yeast are bred in such a way as to be acclimated to sulfites. They can withstand the levels that are typically present after a dose has been added to a wine. It is true that if a wine fermentation is on the verge of stopping anyway – for whatever reason – that a dose of sulfite can hasten its ending, but not with any predictable consistency. If a dose of sulfite is added to a fully active wine fermentation, you may see it slow down, maybe even to a crawl, but it would then eventually recover and go on to completion, but usually at a annoyingly slower pace than before. What happens is the sulfite will kill a portion of the yeast cells, stunting the fermentation activity, but then the wine yeast would slowly begin to recolonize and continue on with the task at hand.

• Potassium Sorbate:
  Adding potassium sorbate to a wine fermentation will not hinder it in any way. What it will do is stop a wine yeast colony from regenerating itself. The potassium sorbate puts a coating on the yeast cells that make it incapable of reproducing itself. In other words, it makes the wine yeast sterile. This makes potassium sorbate an effective ingredient to add to a wine that is already clear but may have some trace amounts of wine yeast still in it. If you sweeten that wine before bottling, the potassium sorbate will eliminate any chance of these few yeast cells from growing into large enough numbers to create a fermentation within the wine bottles.

As you suggested, you could add alcohol to the wine to stop the wine fermentation. This is known as fortifying the wine. But you would need to get the alcohol level up to about 20% for this purpose. Brandy is typically used for this. It should be noted that this will dramatically change the wine’s flavor. The wine will seem less fruity as the alcohol level rises.

If you absolutely, positively, without question, must stop a wine fermentation in midstream, here’s how a winery would do it:

1. Chill Down The Fermenting Wine:
   The cooler the better, but 50°F. is sufficient. This will stop the wine fermentation, and the wine yeast will slowly begin to settle to the bottom. You may also want to add bentonite while chilling the wine to help the wine yeast clear out faster and more thoroughly.

2. Rack The Wine Off The Sediment:
   Give the wine plenty of time to clear up before racking it. Technically, it is possible to rack the wine in as soon as 5 days, but it is much better to wait a couple of weeks. You could get extra solids precipitating out of the wine during this extra time such as acid crystals. That would be a good thing.

3. Filter The Wine:
   When I say filter the wine, I do not mean to drip it through some cheese cloth or a coffee filter or something along this line. You need to be able to put it through an actual wine filter that will filter fine enough to remove any leftover yeast cells. This means filtering down to .5 microns in size. A coffee filter only filters down to about 20 to 25 microns. A .5 micron filter pad will remove over 99.9% of the wine yeast in a wine and is considered sterile. Depending on how much tannin is in the wine, you may need to put the wine through a more coarse filter pad first. I always filter through a 1 micron filter pad before attempting to run the wine through a .5 micron filter pad. This eliminates the chance of the filter pad being clogging up with wine solids.

So there you have it: how to stop a wine fermentation. My personal opinion is that the effort is not worth it from an individual winemaker’s perspective. It is much less work to let the wine fermentation complete on its own, then deal with adjusting the sweetness to your liking.

Happy Winemaking,
Ed Kraus
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Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.