In the Winery
Vinification in many cases forms a continuation of the viticulture options mentioned in the previous blog. There are several commonly used options for winemakers seeking to stop fermentation to maintain residual sugar: chaptalisation, temperature control, sulphur addition or less commonly, racking.
The method chosen depends on the winery equipment being used, generally new world producers using stainless steel will be able to easily control the temperature of their fermentation. As many traditional producers throughout France and Germany are fermenting in large, old oak foudre the addition of sulphur is vital to halt fermentation. Of course, the naturally high sugar levels in grapes destined for sweet wine production may naturally cause a premature stop of fermentation.
Chaptalisation is a further method of sweetening, however as it relies on the addition of rectified grape must prior to primary fermentation it has more of an impact on the finished wines alcohol level than its residual sugar if fermentation is allowed to complete naturally. Chaptalisation is widely used in marginal European countries however its use is banned from all German and Austrian Pradikatswein and may become more obsolete as a result of climate change.
A more controversial method of sugar addition is the use of sussreserve. This has historically been utilised for the production of inexpensive sweet wines. This involves the addition of unfermented grape juice following primary fermentation to raise the residual sugar level of the wines and help balance searing acidity.
Many of these options are prescribed or controlled by the various appellation laws, especially in Old World regions of production. What is most important for producers of these styles is the find a method resulting in a balanced wine.