Dealing with a stuck ferment
Written by jema
A fermentation may stick (cease fermenting) for a number of reasons.
Cold, too high an alcohol content, lack of sugar, lack of acid or
Dealing with a stuck Ferment
The first thing to do is to check the specific gravity with a
hydrometer, or taste the wine. This will tell you whether the suger has
If it has some more suger solution can be added, or you can consider
the fermentation as complete.
Stuck Ferments and temperature
Yeast will only work within a certain temperature range, and it is
important to realise that the very process of fermention can raise the
temeurature of the vessel by as much as 5c. As the temperature creeps
about 26c, yeast will still continue to survive, but will cease to
produce the enzymes needed for fermentation, but if the temperature
hits 38c/100f the yeast will be killed.
Cold is more likely to be the
cause of a stuck ferment though, and you should endeavour to keep your
fermentation above 16c.
In the case of both heat and cold, a 1
gallon vessel with be more vulnerable to fluctuations in room
temperature, than a 5 gallon vessel.
Stuck Ferment Alcohol Content
If there is still sugar to ferment, then you have to consider whether
the alcohol content is too high or whether there is another problem.
This will be hard to judge unless you have been scientific about taking
specific gravity readings when you started.
Stuck Ferment Nutrients and Oxygen
If you believe the alcohol content is still low, say below 10% or so,
then possibly the ferment lacks acid and yeast nutrient. Add the juice
of half a lemon per gallon and some yeast nutrient, it may also pay to
add a vitamin B1 tablet.
Allow 24 hours for a sign of renewed action. If none is forthcoming you
will need to rack the wine add another yeast starter. Racking the wine
will introduce oxygen which may have been lacking. The yeast starter
you choose should depend on what alcohol content you think the wine has
at this stage. If you think the alcohol level is high, then an alcotec
20% kit, may be just the kick your ferment needs.