Page:A Treatise on the Culture of the Vine and, and the Art of Making Wine.pdf/208

 the vat. It is in this manner, and in consequence of this intestine movement, that a crust, more or less thick, is formed at the surface, which is called the head of the vintage, (chapeau de la vendange).

By this rapid agitation, and by the continual disengagement of these aeriform bubbles, the must is considerably augmeuted in volume, and is raised above its former level in the vat. The bubbles, finding resistance to their volatilization, from the thickness or tenacity of the head, make their way through crevices, and cover their edges with scum. The heat, augmenting in proportion to the energy of fermentation, disengages, at length, an odour alcohol, which spreads itselt over the whole neighbourhood of the vat. The colour of the liquor turns gradually deeper, and in some cases, after many days, and in others, only as many hours, of tumultuous fermentation, the symptoms diminish, the mass subsides to its former bulk, the liquor becomes clear, and fermentation is almost terminated.

Among the most striking phenomena, and the most sensible effects of fermentation, there are four, which principally and peculiarly demand our attention, viz. the production of heat, the disengagement of gas, the formation of alcohol, and the colouring of the liquor. What observation has hitherto presented, respecting these pheno-