Stuck wine fermentations and how to restart them
The ideal conditions for yeast fermentation are:
- Temperature 18 C - 24 C
- Sugar (not more than 1 KG per 4.5 litres or 2 lb per gal)
- Acid PH 3.5 - 5.5
- Nutrients (Diamonium source of nitrogen)
- Tannin (Correct amount)
- Oxygen (The first part of fermentation needs oxygen for yeast replication)
Grape juice has exactly the right levels of Yeast Nutrients, Sugar, Acid , and Tannin and this is why wine from grapes is much easier than wine from other fruits.
Things that yeast do not like
- Exceeding any of the above.
Alcohol is a by-product of fermentation and inhibits the yeast, different strains of yeast can survive different levels of alcohol. Starting fermentation in the presence of alcohol is not good. Yeast gradually build up resistance to alcohol as it is produced and does not do well when fresh yeast are added to an existing brew.
- Rapidly fluctuating temperatures even within the above range
The first thing to do with a stuck fermentation is to gather the evidence and work out what has caused it to stick.
The table below allows you to compare your evidence and know what to do to restart the brew. Most evidence will result in the gradual re-start action being required. #GradRestart
Stuck Fermentation Table
Gather Evidence What the evedence means Action required Could the temperature have exceeded 26 C Greater than 26 C Kill the yeast See gradual restart Is the current temperature too Low Less than 18 C results in a very slow fermentation Raise to 21 C and then maintain it at 21 C Fermentation never started Dead yeast See gradual restart Specific Gravity reading exceeds the yeast's ability
1080 - 1090 wine yeast.
Sugar levels too high. Sauternes yeast has a better ability to handle high sugar levels. Dilute to get to the correct Specific Gravity reading and then use the Gradual restart Specific Gravity reading is 1010 - 1030 Probably started with a bit too much sugar or the temperature fluctuated in the final stages causing the yeast to stop Best not to restart and use this as a desert wine. Be careful in bottling as a slow fermentation may still be happening and this will blow your corks out. Specific Gravity 1005 - 1010
Does not taste very sweet
Normal termination for medium to sweet wines. Best not to restart and use this as a medium - sweet wine. Be careful in bottling as a slow fermentation may still be happening and this will blow your corks out. Specific Gravity less than 1005
Does not taste sweet
Normal termination for dry to medium wines Your wine should be fine. Recall the original ingredients, was there a source of yeast nutrients Without yeast nutrients the yeast does not replicated and fermentation is too slow Add yeast nutrients and leave for 6 Hours if this does not work then See gradual restart Recall the ingredients, was there a source of acid? For those that can measure the ph this should be around PH 4 Yeast needs a source of acid for fermentation and without this fermentation is too slow and has a clinical aroma Add Juice from 1 - 2 lemons for each Gallon on wine. I had a low acid brew that stuck and added lemon juice and it restarted within 30 minutes. If it still does not restart then see gradual restart Recall the original ingredients, was there a good source of tannin. Tannin is found in grapes, raisins and most fruits. Tannin is very low in honey and flowers Yeast needs the right level of tannin to proceed with fermentation correctly. Alas it is not easy to measure Add a source of tannin, grape juice, fruit juice.
See gradual restart
Recall the original ingredients, was there any source of preservatives present. I had this problem when I added some elderflower concentrate that I bought from a super market. It had enough preservative to kill all known yeast Many preservatives kill yeast. Preservatives E211 (Sodium benzoate) and E202 (Potassium sorbate) are used abundantly in supermarket concentrates. These two are particularly good at killing yeast. Pour it away and put this one down to experience. I have been there and it is quite frustrating just how impossible it is to buy concentrates without preservatives. The only supermarket drink I found without E202 or E211 was, oddly enough, cola which I fermented but the end result is not good. UPDATE: The supermarkets have eased off on E numbers and you can find E number free concentrates
Before you proceed with the Gradual restart make sure you have first addressed what went wrong e.g. if too little acid was added then add acid. If too much sugar was added then dilute to correct level. See Table above for full descriptions #StuckTable
Having addressed the initial problem and need to restart the fermentation we need to start with a yeast starter.
- Prepare a yeast starter use (Champagne yeast this is a great restart yeast)
- Sterilize a 1 pint bottle
- add 1/2 pint of cooled water that was previously boiled
- add 1 tea spoon of sugar
- 1 squirt of lemon juice
- a pinch of yeast nutrients
(Must be less than 27 C before adding the yeast)
- 1 heaped teaspoon of restart yeast (Champagne yeast)
- Plug the mouth of the bottle with cotton wool
- Leave for 6 hours
- Add the Yeast starter to an empty container of the same size of that holding your brew.
- Now add an equal quantity of your stuck brew to the container. (Using the above this would be 1/2 pint)
- Leave for 6 Hours
- Now add an equal quantity of your brew to the new container. In our example the new container now holds a pint so add a pint of your stuck brew.
- Leave 6 hours.
- Every 6 hours keep doubling the volume in the new container by adding from your stuck brew until you have transferred to the correct fill line or all of the brew is transferred.
Your Brew should have been restarted as soon as it was introduced to the container with the new yeast starter. If it still did not start you need to look again at the stuck table and work out what is going wrong.
If this has been helpful please let me know and if you are still having problems the email me so that I can help and may be add your specific issue to this page.
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