ALCOHOLIC FERMENTATION

A few producers still ferment their wines in oak (casks, tuns, etc) but most prefer thermostatically controlled stainless-steel vats. Capacity ranges from 25 to several 100 hectolitres and the content of each vat is carefully labelled by cru, pressing fraction, varietal and vintage.

Chaptalisation – the addition of sugar to the fermenting must – is used as necessary to produce a wine with a minimum alcohol level of 11%.

Selected yeasts (saccharomyces cerevisiae) are also added, either in liquid form or as a dried active yeast, to facilitate the control of fermentation. They work by consuming most of the sugar in the grapes, excreting carbon dioxide and alcohol in the process. They also release a large number of molecules (superior alcohols and esters) that have a major effect on the aromas and flavours in the wine. The process is highly complex, usually lasting about a fortnight and causing an exothermic reaction that must be carefully controlled. Temperatures higher than 18-20°C increase the risk of flavour evaporation and may cause the fermentation to ‘stick’ (grind to a halt).

Progress is monitored on a daily basis, checking the temperature and overall condition of the fermentation.