I filtered my wine and everything looked fine, but now I have a residue in my wine bottles that looks and feel like sugar crystals. Where did they come from?
The residue that you have described is commonly called “wine diamonds” by wine makers. It is caused by the crystallization of tartaric acid which was originally in solution and could not be removed by filtration. The formation of wine diamonds is welcomed by some wine makers because it usually only occurs in well made, high quality wines. The diamonds precipitate as the wines are being aged. Cold temperatures accelerate the formation of wine diamonds. If you want to minimize the amount of crystals that will form in your bottles, you can store your wine at just below freezing about two weeks before bottling. This will cause the crystals to form in the carboy allowing you to rack the cold treated wine off the residue.
