Cap

(chapeau in French), the layer of grape solids that floats on the liquid surface during red wine fermentation and requires careful management. The cap usefully limits the amount of oxygen available to the yeast, thereby encouraging the formation of alcohol, but has to be broken up and submerged in order to encourage the extraction of the desirable phenolics which add colour, flavour, and longevity to a wine. See maceration, pumping over, délestage, and punching down.