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What's the white residue on red grapes?

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I've noticed in the last year that red seedless grapes often have a white residue on them. I rinse the grapes and the residue appears to be gone. When the grapes are dry again, the residue appears. what is this? Hopefully, it's not pesticide.

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  1. Natural yeast. There have been recent posts about making sourdough starter with red flame grape yeast, if that's of interest to you.

    3 Replies
    1. re: MobyRichard

      Does this have anything to do with cream of tartar?
      I wonder why this yeast shows up on grapes (and plums?) but not on apples, tomatoes etc.

        1. re: blue room

          Apples naturally have yeast on their skins. This is why unpasteurized cider ferments so readily. However, supermarket apples have usually been washed and oiled or waxed to remove pesticides and to keep the apples from drying out.

      1. No worries about pesticides, even grapes that haven't been sprayed should have a bloom on them. It's a natural waxy substance produced by the fruit to protect itself. Here's a cite from Welch's -
        http://www.welchsfresh.com/faqs.asp