Grape: Skin

The grape’s skin (pellicule in French) is the tough, enveloping layer around the grape that holds it together. The outside layer, or bloom, consists of wax plates and cutin, both of which resist water diffusion and hence water loss from the berry. They also impede penetration of fungal spore growths and other biological infections. This waxy layer forms the grape’s typically whitish surface, called the bloom. The fatty acids and sterols from the bloom supply important nutrients for the growth of yeast, either added or ambient yeast in the atmosphere, during fermentation.