Preparing grapes for fermentation
Once the grapes arrive at the winery they may be deliberately chilled – some hot climate wineries even have cold rooms where grapes may be kept for hours or days until a fermentation vat is available. Even more likely at a top – quality winery in any climate is that the grapes are subject to further selection. One of the most obvious winery innovations in the 1990s was the installation of sorting tables, typically a slow-moving belt, onto which grapes are tipped to be minutely examined before arriving at the crusher or crusher–destemmer. (Mechanical crushing releases the all-important juice and replaces the human foot – still used for some high-quality port.)
Most white grapes are destemmed before going to be pressed because stems can be astringent and would spoil a light, aromatic wine. For some full-bodied white wines, the winemaker may choose to put whole bunches into the press. This is because the stems can as useful conduits of the juice and in any case only the first pontion of it, the so-celled “free-run” juice, may be used.
For white wines a winemaker must decide whether he is going to make it protected as much as possible from oxygen, preserving every ounce of fresh fright flavor (preventing oxidation and stunning yeasts right at the start with added sulphur dioxide, complete destemming, low temperatures throughout, and so on) or to adopt deliberately oxidative techniques, exposing the grapes to oxygen and aiming for secondary, more complex flavours from the fruit rather than the pure, unadorned hit of primary aromas. Riesling, Sauvigonon Blanc, and other aromatic grape varieties tend to be vinified protectively while most tpo-quality white burgundy is made oxidatively. Oxidative handling may include a period of deliberate “skin contact”, not as exciting as it sounds but a few hours either in the press before it is turned on or in a special holding tank during which further flavor will be leeched in to the must from the skins. If the skins are allowed contact with juice for white wine for too long, however, they impart far too much astringence which is why grapes for white wine, unlike red wine grapes whose skins are needed for colour and tannin, are pressed before fermentation.
The harshe the pressing process, the tougher the resultant white wine, however. Over the years presses have been designed with increasing ingenuity to squeeze out the juice as gently as possible, without breaking the pips or extracting astringence from the grape skins. Pneumatic presses, which operate by filling a horizontal cylinder wine grapes and an inflatable rubber bag, are now most common, some of them being completely insulated from oxygen for protective juice handling. Winemakers are increasingly careful to separate different portions of what flows from the press, the earlier juice being the finer and least astringent