The residents of Baltimore just endured one of the coldest weeks in years. Temperatures rarely rose above freezing and wind chills were in the single digits. Unlike most of the city, we’ve been anxiously waiting for it to get cold. We needed temperatures to dip low enough for us progress to the next stage of white wine production: cold stabilization.
Our Vidal Blanc finished fermentation a long time ago. Up until this week, it was doing some bulk aging in our friend Nick’s basement. When our local weatherman began predicting a cold snap, we knew it was finally time. Finally time to put our wine outside on the roof.
You might be saying to yourself, “Putting wine on the roof is not a winemaking step with which I’m familiar.”
I must admit, the roof was primarily a security precaution. Like most Baltimoreans, Nick lives in a rowhouse. Putting the wine on the front stoop, albeit more convenient, would have been an open invitation to devious wine robbers.
While the roof was a safeguard, exposing the wine to the elements was an absolute necessity.
All wine has a high concentration of tartaric acid, which is naturally occurring in grapes. At temperatures below 40 degrees Fahrenheit, tartaric acid forms tartrate crystals. If we bottled the wine before cold stabilizing it, these crystals would form inside the bottles as soon as we refrigerated* them.
Tartrate crystals are natural and harmless, but wine consumers outside of Europe have been resoundingly clear on one point: they will not drink white wine with crystalized specks in it. By dropping the temperature of the wine, we force the crystals to form now. The wine is then siphoned away from the crystals.
Cold stabilization does impact the flavor of the final product and its long-term ageability. The winemakers at Tablas Creek do not cold stabilize the whites that they hope will have the longest aging curve. Red wines are not cold stabilized because they rarely, if ever, see the cold temperatures a white wine does. If the crystals do form, they are less noticeable. Additionally, consumers are more accustomed to seeing sediment in red wine.
Cold stabilization has been an integral part of winemaking for centuries. Before commercial refrigeration, wine barrels were exposed to cold temperatures naturally. Tartrate crystals were left behind in the barrels. In today’s modern wineries, huge refrigerated tanks are used to drop the temperature of the wine to precise temperatures to encourage crystal formation. Being home winemakers, we don’t have a refrigerated wine tank, nor do we have a refrigerator large enough to hold our carboys. Enter Mother Nature.
I hauled the carboys containing our white wine up to the roof and covered them with a black trash bag to keep the elements away and protect the wine from sunlight. As soon as I got back to our corporate apartment, a horrible thought passed through my head: what temperature does wine freeze at? I had terrible visions. Broken glass carboys. Solid blocks of Vidal Blanc ice. Our white wine ruined forever. Caitlin murdering me.
Much to my relief, Google informed me that wine freezes at around 14 degrees Fahrenheit. Baltimore was cold, but it was not 14 degrees for long enough periods of time to freeze the wine.
When the cold snap ended, we brought the wine down from the roof. It was outside for nearly a week. We found a layer of white, crystalline powder at the bottom of our carboys that indicated cold stabilization had been successful. We racked the wine off the crystals into new carboys and added a dose of sulfur to keep microbes away.
All that’s left is a little more clarification (the subject of a future post) and we’ll be ready to bottle.
But wait! I haven’t told you the best part! If you dry out the crystals, purify them, grind them into a powder, and put that powder in a little jar, you can sell it in a grocery store. What’s it called? Cream of tartar! Cream of tartar is most commonly used as a stabilizer – it gives soufflé the firm texture that helps it hold onto the air trapped inside and maintain its signature, voluminous top. So, the next time you eat a soufflé, raise your dessert fork to winemakers everywhere for making it possible. Nearly 100 percent of commercial cream of tartar is harvested from wineries.
*The temperature of the average residential refrigerator, in the high 30s or low 40s, is too cold for most white wine. If you chill your wine in a refrigerator, take it out shortly before you plan to serve it and allow it to come up to 48 to 52 degrees.