Improper Yeast Starting Method
Many packets of wine yeast instruct the user to re-hydrate the wine yeast in warm water for a few minutes before using it. Re-hydration is just a fancy word for moistening the wine yeast.
When following these directions perfectly there are no problems, but quite often we run into situations where the winemaker's water temperature that was used for re-hydration was just a little too warm or the wine yeast was left in the water for too long.
The recommended temperature on the packets of wine yeast we have seen is 95 to 105 degrees F. for about 15 minutes. Believe me when I say these directions give little room for error. For every minute the wine yeast stays a 105 degrees a small portion of the yeast cells are being destroyed. If the water is just a little hotter, say 115 degrees, then the yeast cells are being destroyed at an alarming rate.
So what this means to the home wine maker is that if they rehydrate their wine yeast at too warm of a temperature, or if they keep the wine yeast in the warm water for a longer period of time then recommended, the cell count may become too low to support a proper fermentation.
When preparing the water for re-hydration we recommend always verifying the water's temperature with a wine making thermometer before adding the wine yeast, as well as tracking the amount of time the wine yeast is to be in the water.
Proper Yeast Starting Temperature
Secondly, we also recommend that you shoot for a temperature no higher than 90 degrees And keeping the wine yeast in this water for no longer than 10 minutes. The 90 degree temperature for 10 minutes is plenty to complete the re-hydration process and will result in the destruction of less yeast cells.
To be more frank, if the re-hydration process was skipped entirely it would not be of great detriment to the wine. The yeast would simply take a little longer to start fermenting. Basically this means instead of seeing the first signs of activity in 2 to 4 hour, without re-hydration it might take 4 to 8 hours.
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