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  • Stuck Ferments

    Again many thanks to Pat Cuthbert (moderator Winepress.US and all round good guy!)



    Every once in a while the unexpected will happen, and fermentation will stall or stick. It is frustrating when it does as it throws our plans off track.

    There are several reasons why a fermentation will stick, and if you are watching for them, you can usually get things going again promptly.

    How do you detect a stuck fermentation? The only way is to monitor the Specific Gravity with a hydrometer. Check every couple of days if fermentation seems to have slowed down. Watching an air lock for bubbles is not a practical means to detect a stuck fermentation. Changing air pressure can bring bubbles through the air lock and give you a false indication.

    When can one expect a stuck fermentation?

    Fermentations may stick when the wine is racked from primary to secondary vessels.

    Fermentation may stick when you have experienced large temperature changes or when the temperature has gone too high or too low for the yeast.

    Fermentation may stick when chaptalizing (adding sugar) to make a higher alcohol yeast.

    How do we restart a fermentation?

    Adding another package of yeast may not work. Yeast become alcohol tolerant during the fermentation process. The yeast cells do have a limit at which they will grow and become productive little alcohol makers.

    This limit is quite low when the yeast is first re-activated from their dormant phase so when adding a fresh yeast culture, it is important to acclimatize the yeast to the higher alcohol level.

    This is a slow involved process, but is essential if you wish to finish the wine.

    First, you will add yeast nutrient to the stuck must. Mix it with either water or some of the must and then add it back to the carboy, stirring in gently, but fully.

    Next, rehydrate a high alcohol tolerant yeast (Lalvin EC- 1118 is what I use) according to the manufacturers directions. While this is being done, draw 1/2 cup of the stalled must and add 1/2 cup of water. This dilutes the alcohol and sugars to a level that the new yeast will tolerate.

    When the new yeast has cooled to room temperature (or the temperature of the must) add the yeast to the 1 cup of reduced must. Cover and allow to sit for a day.

    When you see signs of good fermentation (slight foaming on the must) you will add 1 cup of the stalled must. Allow this to begin fermenting steadily and then add 2 cups of the stalled must.

    Continue this process doubling the volume of the new must until you have 1/4 to 1/3 of the must fermenting strongly. You may then add this back into the carboy containing the stalled must. Stir it in gently and your wine should ferment to dryness (or the alcohol limit of your yeast).

    If you are lucky, and have a similar batch of wine ready to transfer into secondary, you may be able to use the yeast from that batch to restart the fermentation.

    To do this you would transfer the active batch to secondary and then rack the stuck batch into the primary you have just emptied. The remaining yeast should be alcohol conditioned and fermentation should take off again.

    The use of yeast nutrient should also be considered for this process.

    Hope this helps;

    Pat
    (Pat cuthbert....moderator from Winepress.US)



    See here also

    Last edited by lockwood1956; 26-04-2007, 10:52 PM.
    N.G.W.B.J.
    Member of 5 Towns Wine and Beer Makers Society (Yorkshire's newest)
    Wine, mead and beer maker
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