I bought grapes fermented for 6 days,has been filtered,smell very sweet,but in the first day I saw white stuff on the surface,
then shake it,haven't seen this,is it safe to drink?
what is the white stuff on grapes?
The white powdery stuff on grapes is the natural yeast blooms and what is responsible for fermenting the wine. The white stuff on the surface was new yeast.
6 days is way too short of a time to ferment IMO. There are two stages of fermentation that need to happen.
During the primary fermentation, the oxygen in the juice is consumed by the yeast and the yeast spends most of the time replicating.
Once an optimum population of yeast is reached, or the oxygen is depleted, the fermentation will progress to the secondary stage.
This stage is where the yeast converts sugar to alcohol in an anaerobic environment.
Anyway, the wine will be safe to drink. Even if wine gets infected (it will smell disgusting), you can actually drink it so don't worry about poisoning yourself.
Since you filtered it, you might want to add a fresh batch of store bought yeast to get the fermentation going again.
BTW, Alcohol is actually toxic to yeast. This means that as the alcohol content climbs, yeast activity declines. Wine can sit for weeks, apparently doing nothing but the yeast is actually slowly processing the residual sugars to alcohol.
To make wine, you should expect to leave it alone for 6 to 8 weeks. A hydrometer will tell you when a good time is to rack it off the yeast deposit. If you don't have one, then one way to tell is to rack the wine off the yeast when it has become clear, and you don't see any bubbles rising in the wine. Taste some. If it's a bit fizzy, then it's too soon.
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