Stuck Fermentation and How to Deal With It

Stuck Fermentation
WHAT YOU WILL FIND IN THIS ARTICLE (hit links to jump sections)
  • Definition and Explanation (Definition)
  • Curious to see if your fermentation is actually stuck (Stuck)
  • Problems with Wine Yeast (Yeast)
  • Causes of Stuck Fermentation (Cases)
  • How to prevent fermentation from becoming stuck (Prevention)
  • Restarting Stuck Fermentation (Restart)
What is Stuck Fermentation?
Fermentation that has stopped before all available sugar in the wine has been converted to either alcohol or CO2.
Why is Stuck Fermentation a Problem?
Your wine will have a lower alcohol level than you either anticipated or desired and a higher level of residual sugar than you planned for or desired, and possibly fermentation could restart later in the bottle causing the bottle to explode or the cork to pop out.
How do I know for Sure if my Fermentation is Stuck?
First make sure your fermentation is actually stuck…
  • If you are using a fermenter with a snap on lid and airlock do not just count on the fact that you do not see air bubbles coming from your airlock, it is possible your airlock and or lid to your fermenter does not have an airtight seal. 
  • If you are in a warm climate make sure your fermentation is not actually finished. The warmer your wine must is the faster the yeast works, so take a hydrometer reading to make sure you aren’t simply finished. Caution: Do not use heat to ferment faster than the suggested temperature for the type of wine you are making. Fermenting your wine too fast can bring a whole host of problems.
  • Using your Hydrometer Measure your Specific Gravity a couple of times each day for a day or so to confirm that your sugar content is not falling or is falling at a rate too slow to complete fermentation within about 10 to 16 days. Check out our Article on How to Use a Hydrometer.
Tips for efficient Wine Yeast
  • Make sure the environment you’re making wine in is not too hot nor too cold
  • No killer additives are present (pesticides & sulfites)
  • Plenty of food for it to eat up (vitamins & minerals)
  • Reside in clean and sanitary conditions
  • Oxygen is accessible (vital for starting fermentation process)
Causes of Stuck Fermentation
  • Extreme fermentation temperatures - Too high or too low.
  • Unsanitary equipment - Dirty or unsanitary equipment increases the possibility that microbiological factors bacteria that can spoil your wine. Wash thoroughly before using.
  • Yeast rehydrated at too low or too high a temperature - This can kill a large percentage of yeast cell population, which does not leave much left for fermenting.
  • Old yeast - Weakened or expired yeast, will cause your end products taste to be semi-sweet and not have full flavor.
  • Incorrect yeast – Make sure when choosing Yeast to properly choose the correct one that will work with you must best.
  • Yeast not rehydrated before pitching - Rehydrate yeast according to manufacturer's instructions. Most dry yeasts will work without rehydrating before pitching, however rehydrating is typically recommended by the yeast producer
  • Temperature shock when rehydrated yeast is introduced to must – Try not to allow more than a 5-7° C differential between yeast mixture and must.
  • Excess of CO2 in your wine – Very important not to forget to degasss.
  • Sulfite levels too high - adding too much metabisulfite; failing to wait 24 hours after Campden applied to must before pitching yeast; or high must pH, which can lead to high fermentation rate.
  • Pesticide residue on the exterior surface of grapes or fruits - wash all grapes or fruits well before processing.
  • Lack of nutrient – Yeast’s need nutrients to stave off nitrogen or certain amino acids.
  • Extremely high starting SG - too much sugar in must at the outset.
  • Sugar has all been utilized - you don't want your starting SG to be too low either!
  • Naturally occurring sorbate in must - as in the case of blueberries.
How to prevent Stuck Fermentations
  • Monitor and confirm your fermentation temperatures are at the correct levels.
  • Evaluate your equipment to make sure they are sanitary for efficient use.
  • Double check and make sure the yeast you use is fresh.
  • Use the proper yeast for the wine you're making, not every wine will acquire the same.
  • Rehydrate yeast before pitching.
  • Pitch the yeast within 20 minutes of rehydrating it.
  • Maintain proper free SO2 levels - the amount of metabisulfite to add to your wine depends on pH of wine.
  • Add yeast nutrient before pitching yeast
  • Keep your starting SG to reasonable levels (1.090 - 1.100 or lower). Hydrometers are needed, purchase one if you do not own one already.
  • The must will need to aerated, just before pitching the yeast; do this by stirring the must strongly. This will produce the oxygen needed to start the fermentation.
How to Restart
  • Bring must up to proper temperature, typically 70-80° depending on your yeast. Check out our Wine Yeast Reference Chart
  • Aerate it by stirring the must, the yeast needs oxygen to work properly
  • Before re-pitching yeast, add additional yeast nutrients to the must
  • If the prior three methods fail, re-pitch your yeast