Glad you did the experiment and tested out how this worked in your kitchen, but I'm not surprised that the wild grapes weren't as successful as the whole wheat. The current research we have about wine grapes and yeasts says that the outsides of fresh, whole grapes actually carry very, very, very little Saccharomyces cerevisiae. Those data are for cultivated wine grapes, not wild grapes, but we also have evidence that human activity is a major source of spreading yeasts in cultivated vineyards, so wild grapes aren't likely to harbor more yeast. It makes sense that we'd think yeast hang out on grapes, since grapes will ferment spontaneously once you crush them, but the yeast come in from other surfaces and only settle in grapes once they've been broken open to expose their sweet juices. Your experience is coherent with those studies!

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