Cold Stabilization (CS)

Wine in cold stabilization.
Complete with snow!

      Below is a carboy of Niagara White that has gone through cold stabilization. Note the crystal formations around the carboy and on the bottom. CS is important (mostly for whites, and sweeter grape wines) because when wine is exposed to low temperatures,  tartrate crystals precipitate out and fall to the bottom giving the appearance of broken glass in the bottle, and this may freak out some folks into not wanting to drink it. CS also helps to lower the acidity (TA) and raise the pH of a wine that may have a slightly higher TA level than is desired.

      My approach to CS is to get it to around 28-30F for 2-4 weeks. No one has their fridge down that low and hopefully no one will put my wine into a freezer! Brrrrr! I do this for whites and sweet red grape wine because those are the wines most likely to be chilled prior to drinking as compared to dry reds. These are typically consumed at cellar temperature and only need to be exposed to cellar temps.

      Once the wine is done with CS, it is tested for Free Sulfite levels. The necessary SO2 is added to the receiving carboy and the wine is transferred or "racked" off of the tartrate crystals into a clean carboy.

See here for a in-depth look at CS - https://www.extension.purdue.edu/extmedia/fs/fs-54-w.pdf