Signs of a stuck fermentation are no air bubbles through the airlock even when the lid is pushed down gently or there is no movement in your hydrometer reading. However there are a few other things to check first to be absolutely sure your wine has stopped fermenting:
- The lid of your fermenting vessel, if this hasn’t created a seal CO2 may be escaping through the lid instead of through the airlock. So it could still be fermenting but with very little evidence of it.
- The temperature may have fallen: The ideal temperatures to brew wine at are between 21-26 degrees if it falls below this fermentation will slow down or stop completely.
- Your wine may have fermented quickly and it may be that it has finished. The only true way to know whether your wine is fermenting or not is with a hydrometer reading. Take two readings over 48 hours if they have changed ferment on until they remain the same.
What causes a stuck fermentation and what to do about it?
- Lack of Sterilisation: Yeast needs a clean environment so you can use sterilisers and sanitisers like VWP, Brewsafe and Starsan. These will ensure there is no bad bacteria to disturb the yeast.
- Temperature: As mentioned above the temperature has to be correct, wine yeast likes it to be not too warm and not too cold, if it’s far too hot it may harm the yeast or possibly kill it. If so you will need to add a restart yeast. High temperatures can also result in very lively fermentations which can create off flavours in your wine.
- If your wine has cooled to 18 degrees fermentation may slow down or stop completely, bringing it back up to between 21 and 26 degrees will start fermentation again.
- Oxygen: Yeast needs oxygen to create a comfortable fermentation environment so giving your must a good stir can help kick start fermentation.
- Use the correct yeast: If you’re making a wine kit use the yeast provided or if you are making a wine from scratch you can use an individual fruit yeast or super wine yeast compound which is a mixture of nutrient and yeast making it perfect for fruit wine making. It will ferment up to an approx ABV of 14%.
- Old Yeast: Using old yeast can mean that fermentation never started.
- Specific gravity reading too high (1080 – 1090): High levels of sugar can result in high levels of alcohol and depending on the yeast a high level of alcohol will kill the yeast. Sauternes yeast can handle high levels of sugar and from the Gervin range GV7 can be used to kick start fermentation. Another method is to water down your must to dilute the sugar down to the correct level. Again a hydrometer reading can tell you whether you are at the right level.
- Preservatives: These can be added unknowingly by using juice from the supermarket and many will kill off the yeast. Preservatives such as Potassium Sorbate effect the reproduction capabilities of the yeast and therefore stop fermentation. Check the label before buying as preservative free juices are available.
Hope this helps and contributes to trouble free wine making!