This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
Yeast tends to beat out most competitors because of its ability to live
in an alcoholic solution, while bacteria and fungi tend to die even at
low alcoholic percentages (though some can live almost as well.) It
also survives well because of its rapid reproduction rate compared to
However small infections can occur and spoil the odour and flavour of
wine. You're unlikely to get sick from these infections, since anything
bad will almost always SMELL bad too, and taste worse. To avoid this,
keep everything that comes in contact with your wine very clean. This
is especially critical when cleaning the fermenting vessel. You don't
need to sterilize, as it is impossible to keep things sterile. A
solution of bleach water (one capful per gallon) will kill almost
anything. You'll need to rinse off all the bleach since yeast have
trouble living in the presence of chlorine and even the tiniest amount
can produce awful flavours and odours when it reacts with other things
in your must.
If a fermentor has just been in use and you're rinsing it out to put
more wine in immediately, scalding hot water out of the tap will do
nicely, no need to use bleach. You SHOULD bleach if this last batch had
vinegar in it.
A sulphite sanitizing solution is 1 tablespoon of sulphite crystals per
gallon of water.