Wine Diamonds: The Untold Story

Brad Post:

The adage goes something like this "diamonds are a girls best friend" but what about wine diamonds?  Perhaps you've encountered crystalline structures attached to the underside of your cork or maybe noticed sediment in the bottom of your wine glass and wondered what was wrong with your wine.

Are Wine Diamonds the new best friend of girls or are they indicative of bad wine?

Some background. Wine contains three primary acids: Tartaric (most abundant), Malic, and Citric (least abundant) and are responsible for the sour taste in wines.  There are preferred ranges of total acidity (TA) for white wines (6-9 g/L) and red wines (5-7g/L) - (notice white wines acidity is higher).

In the Midwest, the cold-hardy varietals that we are able to grow, and make into good wine, tend to push the envelope of high acidity. (The Frontenac grapes from this year were picked at 21 Brix and 16 g/L TA - crazy-high!). Reason for high-acid?  Either the grapes were harvested before they are fully ripened or may just be an artifact of the varietal being grown.

Back to the questions:  Are wine diamonds the new best friend of girls or are they indicative of a fault?  No.  No, is the answer to both questions.  Although interesting to look at and harmless to consume, wine diamonds are simply Potassium Bitartrate salts (or Tartaric Acid crystals) more commonly known by their kitchen cupboard name - cream-de-tartar. These crystals are soluble in juice but less so in wine. And this means that the acids in the juice are invisible (much like sugar dissolved in Kool-Aid) but in wine they can begin to crystallize and precipitate (fall out of solution) and ultimately collect on the cork or inside at the bottom of your bottle of wine.

In my next blog, I'll explain how winemakers try to minimize the chance of crystal formation and explain what I do around the winery to aid in the stabilization of wine.

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Brad Johnson is a contributing writer for Make Mine Wine Magazine, an artisan winemaker, researcher, teacher, and proud member of the Eastern Iowa Wine Club. He Tweets as "Iowine".