It's grape season! I've got a few scuppernog vines (that's the grape native to the US, Vitis rotundifolia) in the yard. They are bearing grapes plentifully. Scu

It's grape season! I've got a few scuppernog vines (that's the grape native to the US, Vitis rotundifolia) in the yard. They are bearing grapes plentifully. Scuppernogs have a thick skin, much thicker than the European kind (V. vinifera), with astringent flavour (that's polyphenol tannins) . When you look at the surface closely you see little corky spots, where the hypersensitive response took place, a defense mechanism in plants against fungal infection. The tannins denature cellulase enzymes that are secreted by fungal hyphae in their attempt to invade cells, and cork is dry and just plainly indigestible. Indeed, scuppernogs have an excellent reputation for disease resistance. The xkcd is very relevant, also for grapes.