Tartrates on cork - what does it mean?

I just opened a bottle of 2005 Lazy Creek Pinot that I bought at auction recently. My CT note is posted below. When I pulled the cork, I noticed that it was saturated more than halfway up (unusual but not unseen for a well-stored bottle of this age) and loaded with tartrates. From what I’ve read, although tartaric acid crystals in wine are “natural” and not a cause for concern, it seems they may precipitate out due to temperature changes. I have not often seen significant tartrate accumulation in bottles from my cellar, even old bottles from the '70s/'80s. But my father kept his wines in his crawl space (not sealed, so subject to temperature fluctuations) when I was a kid, and I remember a lot of his '80s BDX having significant tartrates on their corks. So my question is, are high levels of tartrates a potential warning sign that a wine has seen significant temperature fluctuations? Or could it just be more likely to occur in high acid wines (like this Lazy Creek)?


  • 2005 Lazy Creek Vineyards Pinot Noir - USA, California, North Coast, Anderson Valley (4/21/2021)
    This has aged pretty gracefully, despite a cork that was half-saturated. Dark ruby color, youthful, with a pretty nose of raspberry and sour cherry. Has a healthy dollop of acidity, with tart cranberry flavors and a bit of smoke on the back end. I was first introduced to Lazy Creek by my sister more than two decades ago when she lived in California. At the time, I was becoming enamored with AV wines, and thought they were a quality producer, offering good value, that flew under the radar. It’s nice to see that their wines can age well too. (89 pts.)

Posted from CellarTracker

It’s a sign of wine having been subjected to cold temperatures, not having been chill-filtered and often being high in tartaric acidity.

The solubility of tartaric acidity in wine changes with the temperature. If a wine is naturally very high in tartaric acidity, it can be close to being saturated in tartaric acidity. If you put a wine like this in fridge temperatures, the solubility of the tartaric acidity drops down below the level of taratric acid in the wine, so the wine becomes supersaturated in tartaric acidity. In this event, tartaric acidity starts to drop out from the solution as tartaric crystals and the process continues until equilibrium is reached, i.e. the wine is not longer supersaturated. These crystals don’t dissolve back into the wine.

Chill-filtering means that a wine is chilled down so that tartaric crystals start to develop and drop out from the solution. Then these are filtered away from the wine before bottling so that a customer can pop their bottle in a fridge and the producer doesn’t have to worry about wine crystals forming in the wine.

So if you find tartaric crystals in a wine, it’s a sign that it has been subjected to cooler temperatures or there have been other chemical changes (for example due to aging) that has lowered the solubility of tartaric acidity below the amount of tartaric acid in the wine. However, nothing alarming - unless a wine has been frozen, it is not a warning sign that anything alarming has happened. And often if a wine freezes, it pushes the cork out a little bit.

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I see the crystals a lot with high acid reds and think of them as a welcome sign that the wine has not been messed with to much.

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It’s all sound and fury, signifying nothing.

You really answered your own question with the info you put in your OP.

Otto covered a lot of great material in his post. I have two points to add.

In the vast majority of cases, those crystals are specifically potassium bitartrate (we use KHT as a shorthand), and as such their formation depends on the concentration of both tartaric acid and potassium in the wine. Some wines with lower tartaric acid concentrations will still crystallize KHT if they have very high potassium levels. Potassium in wine comes from the grape skins, so you do see this in some red wines with somewhat lower tartaric acid.

KHT is less soluble in ethanol than in water, so most wines are in fact supersaturated in KHT (as anyone who has monitored TA/pH during fermentation and seen KHT crash out of solution will testify). However, wine naturally contains compounds that inhibit the crystallisation of KHT, including anthocyanins and other phenolics (so some red wines can better resist KHT precipitation) and mannoproteins (which come from yeast autolysis - so you rarely see these crystals in Champagne, despite high tartaric acid).

It gets more complicated than that, too, but I hope these examples help to illustrate that there are few hard and fast rules about how and why tartrates crystallize in wine. Cold temperatures will make it more likely, but the presence of these crystals in and of themselves does not necessarily indicate exposure to cold temperatures, especially in older wines.

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Same here.

I did once have a shipment of Barbera where every bottle looked like a snow globe, I suspect the truck had been parked in a frozen lot overnight. The wine still tasted fine.