This past winter, a number of the tours that came through wanted to know what was going on with this situation out in the cellar:
One tank, covered in ice. Standing next to a number of others that weren't.
This is part of our pre-bottling process, and it's known as cold stabilization. At low temperatures, the tartaric acid in the wine is less soluble than it is at warmer temperatures. When this happens, crystals of acid begin to form and drop out of solution. And the thing about this crystal formation is that ithis can encourage even more crystals to form. It's okay for this to happen in tank, when we can remove them through racking or filtration, but it can be a little concerning to see it in bottle.
This is less of a problem for red wines, which most people tend not to refrigerate, but when it comes to white wines that can sometimes hang out in the refrigerator for months, cold stability can become an issue. They won't harm you, but they do have a tendency to look like shards of broken glass. (I think it goes without saying that about 99% of us don't really want to ingest broken glass.)
Once we decide on our final blend for a wine, we get all the components into a tank, and then set the tank temperature to below 30 degrees Farenheit. We want to blend first, because even minor changes in alcohol percantage, pH, or other chemical components in the wine can play a huge part in changing a wine's cold stability. Depending on the results of the cold stability testing we do prior to blending, we may add a small amount of cream of tartar, which encourages crystal formation. And then we wait. We'll hold a tank at this temperature for anywhere from 3-30 days. Some wines just require a little more time to stabilize than others.
Once we've determined that the wine is stable, we'll filter, and call it a day. This doesn't mean that you'll never see a tartrate crystal in a bottle from us, but it does mean that under most standard wine storage conditions, your wine should remain clear. We probably can't help you if you tend to sip your wine through a 35 foot long frozen metal straw, but for the rest of you, we've got your back.