Why Did My Wine Stop Fermenting Top Causes And Solutions

There’s nothing more frustrating than eagerly checking your fermenting wine, only to find it stubbornly silent. A sluggish or Stuck Fermentation can turn your winemaking dreams into a vinegar nightmare. As a seasoned winemaker, I’ve seen (and rescued) countless fermentations gone awry. Let’s troubleshoot the usual suspects and get your wine back on track.

Weak Or Struggling Yeast

The Problem: Why Is The Wine Yeast Weak?

Not all yeast is created equal. Old, improperly stored, or low-quality yeast may lack the vigor to power through fermentation.

The Fix:

Always use fresh, wine-specific Yeast and never use Yeast intended for another purpose like bread making. You should always choose a Wine Yeast variety with the traits that compliment the style of wine you’re making. Companies like Lalvin have a huge range of Yeast varieties designed to create almost any style of wine.

Always activate your wine Yeast before adding it to your Must, by making a Yeast Starter. A Yeast Starter is created by adding your Yeast to a sanitized Glass Jar with water, sugar and Wine Nutrient Salts. The primary purpose is to check your Yeast is active before you add it to your precious Must. There are other advantages as well.

Learn all about creating your own Yeast Starter from our article How To Make A Yeast Starter.

Too Much Sulfur Dioxide (SO₂)

The Problem: Is Too Much Sulfur Dioxide A Problem?

While Sulfur Dioxide (SO₂) protects against spoilage, overdoing it can smother your wine Yeast before fermentation even begins.

Campden Tablets are a common source and are made from either Potassium Metabisulfite or Sodium Metabisulfite, both forms of Sulfites. Their main job is to sterilize your fruit juice (Must) by blocking unwanted bacteria and Wild Yeast. They’re also handy for removing Chlorine and Chloramine from tap water. Especially useful if you’re using municipal water in your wine making process. So you can now understand how having some Sulfites present is a good thing, however having too much will stop your chosen Yeast from transforming your Must into wine.

The Fix:

Test free Sulfur Dioxide (SO₂) levels. Aim for less than 50 ppm (parts per million) pre-fermentation. If levels are too high, let the must sit uncovered for 24 hours to off-gas. Another option is to vigorously stir your fruit juice (Must) with a sanitized long handle spoon. This will help dissipate the Sulfites into the air.

The reliable way know if excess Sulfur Dioxide (SO₂) is the problem, is to test with a kit. It’s not something you can do without purchasing a test kit. I recommend the Sulfite in Wine Titrets Kit as these are reliable, easy to use and make a good addition to your wine making supplies.

Temperature Is Too Low

The Problem: What Temperature Is Too Low For Yeast?

Yeast is like a bear in winter, it slows to a crawl when cold. Below 12°Celsius (54° Fahrenheit), fermentation may stall entirely. For those of us that Ferment in winter, this is a common problem. It highlights how important a temperature gauge is to a winemaker. I recommend the type that stick onto the side of your Fermentation vessel. These are cheap to buy, effective and essential.

The Fix:

Move the Fermenter to a warmer place and keep it at approximately 15° to 20° Celsius (60° to 70° Fahrenheit). Wrap the Fermenter in a towel to help keep the temperature stable. Temperature fluctuations are not good for your wine either. To ensure the correct temperature and minimize change, I recommend using a Fermentation Belt or Fermentation Heating Pad to ensure your Fermenter is within the correct temperature range. I prefer the Fermentation Heating Pad as it wraps the whole Fermenter.

Temperature Is Too High

The Problem: What Temperature Does Wine Yeast Die?

As a general rule, Yeast gets stressed and dies off above 40° Celsius (105° Fahrenheit). This will leave your wine sweet and unfinished. Too high a temperature is a major contributor to Stuck Fermentations during summer time.

The Fix:

Move the Fermenter to a cool place away from heat and sun light. Cool the Fermenter with a wet towel or place it in a shallow water bath. Again, aim to keep ambient temperatures steady.

Acidity Is Too High

The Problem: What Acidity Is Too High For Yeast?

When acidity is too high, that is a pH below 3.0, Yeast can be shocked into hibernation. Fermenting fruits with a high natural acid content like Citrus are more susceptible to this problem.

The Fix:

The first thing to do is test the pH with a pH Meter or pH Strips. I recommend using a pH Meter as they are far easier to use. A well formed Must will have a pH between 3.0 and 4.0 to support wine Yeast. Being able to test the pH of your Must is essential for every winemaker.

To increase pH (lower acidity) add 1/4 teaspoon of Calcium Carbonate (CaCO₃) powder. Calcium Carbonate will neutralize excess acid. Replace the lid of your Fermenter and leave for 24 hours. Test a fresh sample of your Must with using your pH Meter to determine if the process needs to be repeated. Once your Must is within the optional pH range, allow 2 days for Yeast to come back to life.

Not Enough Nutrients For The Yeast

The Problem: What Nutrients Does Yeast Need?

Yeast needs more than sugar to thrive, it craves nitrogen, oxygen, vitamins, and minerals. Yeast that is starved quits early.

The Fix:

Add Yeast Nutrient to your Fermenter to boost available nutrients in your Must. Yeast Nutrients are usually a combination of Ammonium Phosphate, Potassium Phosphate and Magnesium Phosphate. I recommend buying commercially made Yeast Nutrients like the Fermaid O brand. These are cheap to buy and easy to use, so be sure to follow the instructions carefully.

Final Words: Restarting Stuck Fermentations

Winemaking isn’t magic, it’s about science and precision. Mastery means knowing why things go wrong, and exactly how to fix them. Don’t just hope for the best, plan, take charge, make adjustments, and trust the process. Your patience and attention to detail will be rewarded with a wine worth bragging about.

It can be frustrating if a fermentation becomes stuck despite your careful preparation, but with the right know-how, you can troubleshoot and get your wine back on track. Whether it’s testing acidity, stabilizing temperature, measuring sulfur dioxide, or ensuring proper yeast nutrition, each step brings you closer to a restoring proper fermentation. 

Don’t let a sluggish ferment derail your winemaking passion. Armed with these solutions, you’re equipped to diagnose issues early and take action with confidence. For more insider tips and expert advice, explore our other guides and join a community of home winemakers who refuse to settle for anything less than exceptional

Ever resurrected a seemingly doomed fermentation? Drop us a note and share your heroics, we’d love to hear from you.