Most winemakers will encounter a "stuck" ferment at some stage during their winemaking "career"...they can take a bit of detective work to fix!
What is a stuck ferment?
When the fermentation has started out well enough but just seems to stall at some stage during the fermentation process.
How do you know you have a stuck ferment?
If the bubbles stop coming through the airlock and you cannot see any "activity" in your wine you may have a stuck ferment BUT your fermentation may just be finished. If you have a hydrometer you can check the SG (specific gravity) of your wine to see if there is still sugar in it. Follow the manufacturer's instructions as different brands seem to have a different scales but in general terms if your SG is 1.000 or below, your fermentation is finished. If you don't have a hydrometer you can taste the wine, if it is still at all sweet (unless this is what you intended by using a lower alcohol tolerance yeast) the fermentation is not yet finished.
The other way to check if you have a stuck ferment is to check the SG using a hydrometer a few days running; if the SG is not changing (and is above 1.000) then you have a stuck ferment.
What causes a stuck ferment?
The causes are wide and varied but generally come down to 2 major reasons: the yeast started off in some way damaged (not fresh or water was too hot or yeast got left somewhere hot like a hot car) and/or the environment for the yeast was not ideal.
Freshness of ingredients
When you purchase your products from makewine.co.nz they are always fresh and of great quality. We are confident in the quality and freshness of our ingredients that we offer 100% guarantee and will give you a refund or replacement as you wish.
Please store your yeast in the fridge.
Fixing a Stuck Ferment by Improving the Environment for the Yeast
When you strain your must after the primary fermentation it is best to leave it to hang for an hour or longer, so as much yeast as possible that is residing in the pulp of the fruit makes its way in to the strained must.
Oxygen. Your yeast needs a certain amount of oxygen to ferment. Aerate your must at the beginning of secondary fermentation by tipping from container to container or shaking a container vigorously for a minute or so. If your ferment sticks, you may be able to restart it by aerating it.
Temperature. The ideal temperature for fermentation is about 18 degrees C. If the temperature is too hot (above 35 degrees depending on the type of yeast) your yeast will die. If the temperature is below 10 degrees the yeast will become dormant but will not die. If you warm up your wine again, the ferment will start again. You can keep your wine warm by putting it in the hot water cupboard or standing it in a bucket of warm water. You can also buy heat pads and heat belts.
Alcohol Content. Different yeast strains have different alcohol tolerances. If you started your fermentation process with too much sugar, your wine may reach the alcohol content where the yeast starts dying off before all the sugar has been fermented. You can fix this by adding more water, but this will also water down the flavour of your wine. You can also blend it with a dry wine.
Acidity. Yeast requires a PH of 3.5 to 5.5 (this is acidic). Some fruits eg grapefruit may be more acidic than this so you may need an additive to reduce the acidity. You can use baking soda or calcium carbonate. You can increase acidity by adding acids (citric and/or malic and/or tartaric). You can buy expensive acid testing kits or you can use litmus papers.
Sugar Content. Yeast needs sugar to ferment, all fruit has sugar, so it is unlikely that your ferment has stuck because of insufficient sugar. However, if you have insufficient sugar your wine will not have enough alcohol and may not keep very well. If you add too much sugar your yeast may have difficulty starting to ferment. If your SG is above 1.100 this may be the case. If you don't have a hydrometer and you taste your wine/must and it is very, very sweet (like a cordial syrup) this may be the case. You can fix this by adding more water.
Yeast has died. It is possible that much or all of your yeast has died when your ferment has stuck, particularly if it takes a while to get it restarted. You may find restarting the ferment more successful if you rack your wine off the lees (sediment) which will consist of alot of dead yeast and add new yeast.
Insufficient nutrients. It is possible to have a successful fermentation without nutrients but you will have more consistent success if you use quality nutrients. We recommend you use GO-FERM Protect at the yeast rehydration stage and add Fermaid A at the beginning of secondary fermentation. There are other less scientifically advanced yeast nutrients you can buy which are usually made from diammonium phosphate and potassium phosphate and vitamin B1 (thiamin).
Replacement Products:
If you think you need replacement products (we will send 5g EC-1118 which is the best yeast for restarting and 6g Go-Ferm Protect) please email the following information to info@makewine.co.nz :
This information will help us ascertain what needs to be done to fix the problem and how to avoid the problem in the future.
© 2011 Karen q Temple
