In my previous blog on my start of making white wine from my estate grown Vidal Blanc, alcoholic fermentation had completed and I was allowing the gross lees to settle and compact. Well that went well and I have racked the clarified wine off of the gross lees into cleaned carboys. I then topped these off with more wine and added a bit of cream of tartar to seed the wine in order to begin the next very important process in white winemaking – cold stabilization.
As I don't have temperature-controlled tankage to induce cold stabilization, I have to rely on Mother Nature to provide the proper conditions to bring on this physical-chemical process. So out to my back deck goes all my white wine carboys. What is cold stabilization and why is it necessary? Cold stabilization is a winemaking method that induces tartaric acid to come out of solution and form a tartrate crystal – also know as wine diamonds. This precipitate either adheres to the sidewall of the carboy or drops to the bottom. The issue with wine diamonds is primarily one of aesthetics. If you don't cold stabilize prior to bottling, it is highly likely this precipitate will form in the bottles when the wine is chilled to the appropriate drinking temperature. It isn't harmful, but it does appear as a wine flaw. So after the cream of tartar (seed) is added and the wines are given a good mix, they spend a number of weeks outside subject to, hopefully, subfreezing temperatures (26 °F/-3 °C is the target). This year I was lucky and we ended up having a stretch of very cold temperatures in late fall and a significant amount of precipitate is evident in each carboy.
An additional benefit of cold stabilization, especially with a high acid grape like Vidal Blanc, is the precipitation of tartrates helps to reduce that acidity a bit, which eases balancing that acidity later in the process. So, shortly I'll be bringing the white wines, back to the wine cellar for the next process – filtration.