What Are Those Shiny Crytals on the Cork?


Question from Steve: I opened a bottle of white wine and it had these shiny crystals, kind of like sugar on the cork. Is that wine okay?

Reply: Hi, Steve. Thanks for writing! Yup, it should be just fine.

A great thing about wine is that even if it’s spoiled it’s not harmful – unless you drink too much, of course! The worst thing that happens is you’re offended by the smell or taste, in which case you should take it back or dump it.

MAJOR DIGRESSION: Please don’t use bad wine for cooking. That weird flavor is what you’re adding to the dish, just like any other ingredient, and cooking it down will just concentrate the weird flavor.

So, what’s with the crystals? It’s really quite common to come across them, especially in white wine. They’re not sugar – they’re mainly composed of tartaric acid, which is a very strong acid, and the main acid found in white wine. As you see, they can also be suspended in the wine.  When the wine is cold for a prolonged period of time – maybe in your fridge, the retailer’s fridge or a very cold ware house – they get together with potassium to form these crystals. Lab speak is potassium bitartrate, which is the same as cream of tartar. Sentimentalists like to refer to the crystals as “wine diamonds.”

Many wineries get rid of most of the tartrate crystals in their whites by chilling the wine in a storage tank before bottling and then filtering out the crystals. Other producers prefer not to. It doesn’t seem to make a difference one way or another, other than the visuals.

Red wines can form reddish looking tartrate crystals too. If you visit a winery, sometimes you see them shining in an empty barrel. They’re really quite pretty.

So, not to worry. Down the hatch. And, of course next time it happens you can look very in the know and worldly by telling your friends not to worry about them – “They’re just tartrates.”

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