February 2023: Understanding Tartrate crystals in wine

Wine Crystals: Gifts from the Grapes

I recently received an email from a long time customer. She wrote, “My husband & I enjoyed the Novello wine tonight and when we were finished I happened to find something odd in my glass.  Is this normal?  Thank you.”

After viewing the photos, I knew instantly what was in their wine glasses - “Wine Crystals” or more lovingly, “Wine Diamonds”. They are formed from tartaric acid which is naturally occurring in all wines and provides structure, balance and flavor. To me, these are gifts from the grapes showing up in our wine. They are safe to consume, albeit crunchy to the bite. They settle to the bottom of the wine bottle and are usually only in the last glass of wine poured.

So, where do these crystals come from? I know that the wine was filtered as it went into the bottling system. Seemingly appearing by magic, there is an actual scientific explanation…

Grapes are composed of different acids in their juice which gives the resulting wine ageability and a lively vitality that makes it enjoyable to consume. Citric acid (think citrus fruits), malic acid (think apples and pears), and, in most abundance, tartaric acid are all constituents of grape juice. It is their individual solubility that concerns us with wine crystals.

Tartaric acid’s solubility in wine is temperature-dependent. When a wine is chilled to temperatures below 40 degrees Fahrenheit, the remaining tartaric acid will bind with the naturally occurring potassium in the wine to form crystalline deposits (potassium bitartrates), or tartrates. As a winemaker, I chill my bulk wines, particularly white wines and high acidity red wines, in a process called “Cold Stabilization”. In this process, I bring the temperature of the bulk wine below 40 degrees Fahrenheit to bring the tartrate crystals out of solution before it is bottled.

So, in the case of this Novello, I did not bring the temperature down enough to cold stabilize the wine before it was bottled. This was due to the higher than normal tartaric acid levels in the grape used to craft the Novello - Chambourcin. Chambourcin is a French-American interspecific red hybrid grape variety used for making wine and survives the cold climate of our Palisade high-altitude vineyards. Chambourcin is notorious for having high levels of acidity which make it challenging to cold stabilize. In this case, the red wine that was bottled was not cold stabile. So, when bottle aged in our wine cellar having an average Winter temperature between 40 - 50 degrees Fahrenheit, the “Wine Diamonds” magically showed up in the bottle.

This process actually improves the wine, creating an even smoother wine tasting experience. Older vintages are notorious for having wine crystals form on the glass of bottles themselves and are a sign of high quality. Sommeliers will filter aged wines into carafes, pouring them slowly to retain all sediment in the bottom of the bottle.

So, the next time you’re at a dinner party and you see sediment in a wine, take the opportunity to share this knowledge with your wine geek friends and family. It is an endless road of knowledge with wine. A road that would take many lifetimes to explore. Being limited to this one lifetime, I am enjoying every sip and experience with the ones I love. I hope you are as well. To your health - Salute!