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Left
alone, the skins would form a solid cap on the top of the juice. Bacteria would
begin to ferment at the cap–air interface, and the result would be a volatile
acidity problem—the wine would reek of vinegar, and be spoiled. Winemakers avoid
this by keeping the cap moist, either by plunging it regularly, or keeping it
submerged by a mechanical device, or by pumping juice over it.
Plunging,
also known as pigeage, is the most traditional method, and can be done by
machine, or by a special pole, or even by feet. This is typically done with
shallow open-top fermenters. Pumping over is potentially more disruptive,
because of the forces involved, but is more appropriate for bigger, closed
fermentation vessels such as stainless steel tanks. Plunging or pumping over
achieve the dual goal of both keeping the cap wet (preventing it going volatile)
and extracting colour and tannin. |