A
glass fermentation vessel, usually in sized in
gallon increments for brewing
wine in particular (amongst other
alcoholic beverages, like
hard cider, and
whatnot!)
All carboys should be kept
clean, and sterilized before putting any fermentable substance in them. The
contaminants of just some tiny
wild yeast strains or other
little critters can turn your wine into
vinegar.
Sterilization of carboys can be done using commercial brewing sterilizing chemicals,
bleach and water (make sure you rinse well!!), or
boiling water. Boiling water for sterilizing is the safest as far as the brewers I know concur. But damn, that stuff is hot, so I have been known to use bleach and water, let the mix sit for a few hours, scrub with a carboy cleaner, and rinse 3-4 times very well with water.
Any amount of bleach will ruin a ferment.
Bleach kills
yeast, even the good
alcohol making kinds.