The fermentation process
Now, and only now,can the winemaker consider conventional fermentation,the miraculous transformation of sweet grape juice into mucg drier, more complex-flavoured wine. If yeast is put into alcohol,heat, and carbon dioxide.The riper the grapes,the stronger the wine they are capable of making. Fermentation vats naturally warm up as the process gets under way, so in warmerclimates they may will need cooling jadkets to keep the “must”, as the pulpy mixture between grape juice and wine is know , below the temperature at which precious flavour compounds may be boiled off. The gas that is generated can make a winery a heady place at harvest time where the small is an intoxicating mixture of carbon dioxide, grapes and alcoholespecially if the fermentation vats are opentopped, as for some traditional red wines. White wines are made in realed vats so as ti protect the must from damaging oxidation and avoid any browning. A vat full of red must has its own protection, the thick “cap” of skins that float on the surface-which is why open-topped red wine fermenting vats are even a possibility.
Many aspects of winemakeing have been subjected to detailed scrutiny and improvement over the last few dacades, but yeast still presents some mystery and controversy. We will doubtless learn more about the exact effect of differebt species of yeast on different sorts of must. But for now the winemaker’s initial choice is whether or not to use specially selected and prepared yeast, so-called cultured yeast, as opposed to relying on the strains of yeast that are naturally in the atmosphere, called wild or ambient yeast.