Periodically I have mentioned such things as “cold stability” and “protein or heat stability”. These are qualities for which the wine needs to be tested prior to bottling. If these issues are not dealt with in the winery, it is possible that the customer will find acid crystals or tartrates in their wine when they refrigerate it, or a protein haze or precipitation should they leave it in their warm car for awhile while doing some other errands. All wines need to be cold stable. Only white wines have protein stability problems. I will add a caveat here regarding tartrate crystals, however. Should you purchase a wine that ends up having a few crystals in it, there is no cause for alarm and no reason to return the bottle. Sometimes, even after stringent measures by the winemaker, a wine can become slightly unstable again and drop a few crystals. There is no effect on the wine, nor will it harm the taste or the consumer.
After racking your wine a few times, it is necessary to cold stabilize the wine. No pre-test is needed as I always assume there will be some unstable tartrates in the wine. Chilling the wine down to 30 degrees or so for 3 or 4 weeks should do the trick. At this point a small lab filter is used to filter about a 100 ml. sample of the wine, which should always be put into a clear glass container. This will allow you to see any crystals that have formed. It is then placed in a freezer until frozen. When it freezes completely, take it out of the freezer and set it on the counter at room temperature to thaw. If there are no crystals in the bottle, I consider the wine stable. Make sure to check it immediately upon thawing as it is possible that some of the crystals will dissolve back into the wine. If there are crystals, the wine needs to chill a bit longer. Check it again in another week.
There is a product that can be used to hasten the fall of the tartrates rather than waiting for 3-4 weeks as described above. It is potassium bitartrate, which is, guess what? Cream of tartar! What happens is the cream of tartar “seeds” the wine and helps to draw out the natural tartrates in the wine. There is a difference of opinion as to how much you need to use. Basically, it is assumed that more is better, but potassium bitartrate is quite expensive. While I have heard of using volumes of up to 30 pounds per 1000 gallons, I have found that 10 pounds per 1000 gallons works just fine. This is not quite 5 grams per gallon. First the wine must be chilled down to the stability temperature you want, say 30 degrees. Then you must stir the wine while you slowly drop the dry product into the tank. Then the wine needs to be mixed for at least another 45 minutes. This actually works on contact and all that remains to be done is to allow the cream of tartar to settle out, which usually takes several days. Make sure to do the freeze test just in case this does not do the trick. It is better to be safe than sorry. After the wine is stable and settled, it can then be filtered.
Next: But wait, there’s more!!!! Protein stable at the same time?