EXPLAINED Whole-bunch fermentation
Whole-bunch (or whole-cluster) fermentation refers to the practice of not destemming grapes. Whole bunches, stems and all, go directly into a fermentation vat. This would have been considered common practice before World War II, as mechanised destemmers were not commonplace.
Beaujolais can claim to be the spiritual home of the practice, often used with carbonic maceration (where the whole bunches are fermented in sealed vats filled with carbon dioxide, to promote a lighter, fruitier style of wine). Wholebunch fermentation is not limited to Beaujolais, however, with leading names in the Rhône, Burgundy and even Bordeaux choosing to work this way. So why do producers choose not to destem?
• Lower alcohol levels The resulting wine will often be lower in alcohol, for three reasons: stems contain water but no sugar (see box); there tends to be a lower conversion of sugar to alcohol in a whole-bunch ferment; and the use of smaller, open-fermenters means some evaporative loss of alcohol. Set against that, though, the fruit for whole-bunch ferments tends to be picked later, in order to ensure maximum stem ripeness, and that may lift alcohol levels.
• Paler colours Stems absorb colour.
• Lower acidity Stems contain potassium, which combines with tartaric acid in the wine and precipitates, reducing the overall acidity level.
• Freshness Advocates often mention ‘freshness’ as a reason for retaining some or all of the stems (many producers practise whole-bunch fermentation on just a portion of their crop). One reason for the growing popularity of wholebunch is that this freshness might act as a corrective to the sometimes excessive richness which results from the highest quality contemporary red winemaking.
• Profundity Many producers feel it brings something ‘extra’ to a wine – a kind of darkness or sobriety of flavour. Some claim that stems intensify the sense of terroir in a wine, in that the sensorial imprint of the stem must (like fruit) reflect, to a greater or lesser extent, the vine’s site. This is possible but unproven.
Bunches must be meticulously sorted, to ensure that only fully ripened grapes are used. Only then can producers avoid sacrificing precision of flavour while still enjoying the benefits of whole-bunch.