You chilled your special bottle of 2017 Cabernet Franc Rosé and now there are crystals in your glass. What’s up?

In the wine industry those crystals are affectionately known as wine diamonds. What are they? The colorless, tasteless crystals are potassium bitartrate, which is the scary name for the Cream of Tartar (almost all of which is harvested from wineries) that you keep in your pantry. The reason that the industry calls these crystals in the glass wine diamonds is that it is a positive sign of a minimally processed wine that was made from fully ripened grapes.

In the old-world consumers are much more familiar with this condition and are not usually alarmed but in this country, we have become accustomed to crystal clear wine and so when we see something in our glass or attached to the cork it creates apprehension. Needless apprehension.

Tartaric acid is one of the three main acids found in wine grapes, and along with malic acid and citric acid provides the tartness in both grapes and wine. Most white wines go through a second fermentation, after the alcohol fermentation, that transforms malic acid to the softer-tasting lactic acid. Tartaric acid is relatively stable though and is therefore responsible for the maintenance of a finished wine’s pH and its resistance to various kinds of spoilage.

Almost, if not, all wines have some level of dissolved tartaric acid in them, but its solubility is temperature-dependent. When a wine with dissolved tartaric acid is chilled to below 50˚ for an extended period, like in your refrigerator (most of which are set to 34˚) the wine diamonds will form and then it will not dissolve back again into the wine. You rarely ever experience this with red wines, due to the fact that they are rarely kept at 50˚ or less. White wines and Rosés however are often chilled in the refrigerator before they are served and so, minimally processed wines made from fully ripened grapes will form these crystals.

Most mass produced wines will cold stabilize the wine before it is bottled to ensure that these ‘wine diamonds’ are never found in their bottles. This process involves putting the wine into a large tank and chilling it down to as low as 28˚ for a couple of weeks before bottling. The problem is, that in addition to causing the tartrate crystals to form (so they can be filtered out), this process can strip more delicate nuances and subtleties from the wine along with the tartrates.

So…now you know that it is time to celebrate when you find wine diamonds in your glass. Or, if you prefer to not have that experience, just avoid keeping the wine in your fridge for an extended time period. Usually, chilling the wine to 45˚ – 48˚ will be the optimum temperature to enjoy all of the subtleties and nuances the wine has to offer without worry of too many (like;y none) wine diamonds in your glass. Depending upon whether your bottle is coming out of your chilled cellar or is at room temperature the time to reach this optimum temperature would be 20 – 60 minutes. Afterwards keep it in your favorite chilling bucket, but don’t submerge in the ice, and it will stay just right for quite some time.

Lastly, since all of Vine Cliff Winery wines are cork finished, if the bottle is stored or chilled upside down any crystals will form on the cork and with some level of gentleness can be removed entirely with the cork, leaving all the wine in the bottle crystal clear and full of all the flavors and aromas that we meant for the wine to have.