What are those Crystals on the End of a Cork?

Tartrates on the end of your cork!

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  • April 23, 2012

    George Vierra

    Wine Crystals: Wine Diamonds


    On occasion, when a bottle of wine
    is opened, you will notice a crystalline deposit that looks like a cluster of
    coarse salt at the bottom of the bottle or possibly glistening at the end of
    the cork. The clear diamond-like crystals found in wine are potassium
    bitartrate in crystalline form. This is basically the same stuff as the cream
    of tartar in your kitchen pantry.


    The principal acids found in
    grapes, and hence wine, are tartaric and malic acids. These acids are produced by
    the grape as it develops. Potassium also exists naturally in grapes. When the
    wine is under chilly conditions, the tartaric acid and potassium bind together.
    The marriage produces potassium bitartrate (KHT) crystals: wine diamonds. They
    are completely harmless and quite natural. In Europe
    these wine diamonds are accepted as a sign that the wine is a natural one. To
    many these diamonds are even appreciated. Americans, however, are used to wine
    being without the crystals.


    The winery, in order to fulfill the
    consumers’ expectations, forces a pre-crystallization at the winery. This
    process is called “cold stabilization”. It beats the crap out of the wine! The
    wine is chilled to just above freezing; generally 21º to 23º F. It is
    held at this temperature for about two weeks. During that time, the KHT is
    formed in the wine. In order to remove all the KHT, the wine is filtered at
    this cold temperature. The KHT, and host of other things, are removed from the
    wine at this cold temperature. During this handling, the wine also becomes
    saturated with oxygen. That’s a no-no. After the cold filtration, the wine is
    then run through a heat exchanger to bring it up to cellar temperature. But the
    wine must now be sparged with nitrogen gas to remove the oxygen, and again, a few
    other aromatic compounds. Any winemaker who has ever tasted any wine before and
    after “cold stabilization” wants to cry. If the winemaker is patient, this same
    removal of KHT will occur over a longer period of time at cellar temperature.
    Most red wines left in barrels for 12 months or more are not subjected to this
    abuse. Some wineries do not want any of their wines to become “cold stabilized”
    in a hurried fashion. Bravo!


    So, let’s marvel at these little
    wine diamonds. If you’re lucky to find them, raise your glass and enjoy the
    wine with the assurance that this wine has been handled as naturally and gently
    as possible and allowed to attain the highest quality.











    October 2004                                                   George
    Vierra                                                                                        WineCrystals


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