353908 Sat Dec 23 01:19:25 -0800 2006 5 27 General Chowhounding Topics 0 2123878 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. Sat Dec 23 01:19:25 -0800 2006 10025 elise h 1 2123884 Natural yeast. There have been recent posts about making sourdough starter with red flame grape yeast, if that's of interest to you. Sat Dec 23 01:24:04 -0800 2006 2123878 60923 MobyRichard 2 2123895 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. Sat Dec 23 01:29:44 -0800 2006 2123884 42470 blue room 3 2123904 tartaric acid forms in wine barrels Sat Dec 23 01:34:45 -0800 2006 2123895 13150 babette feasts 3 2125431 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. Sat Dec 23 23:13:40 -0800 2006 2123895 11364 Eldon Kreider 1 2125439 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 Sat Dec 23 23:18:42 -0800 2006 2123878 10039 Melanie Wong