Reproduced from Year 5, Issue #25 of Spirito di Vino Asia...
To accompany our columns “From my Cellar” and “Secrets de Chef”, in this issue, we explore how production methods to make sweet wines have a direct influence on its resulting style and quality. The key to understanding this category is to focus on how sweetness is obtained in the final wine.
The first method, concerning what is perhaps the most famous sweet wines of all, those of Sauternes, has to do with a fungus named Botrytis Cinerea, commonly called “Noble Rot.” Indeed, as it implies, this sweet wine comes from rotten grapes. However, for the “noble” kind to develop, grapes must be ripe and healthy at the outset. After several days with gentle misty mornings and dry, sunny after-noons, the fungus gently pierces into the skin of the berries, leaving tiny microscopic holes to allow the water of the juice to evaporate while keeping it intact enough so that it remains impermeable to rain and other bacteria. This gradual process concentrates sugar and acidity, and the spores of Botrytis adds extra complexity reminiscent of marmalade, apricot, and cinnamon. In the cellar, as is the case in Sauternes, the winemaker has the options to let fermentation run its course until the yeast can no longer produce alcohol or stop it through filtration. In either case, the wine has 13-14% alcohol, and the residual sugars are 100-110 g/l. For Tokaj Aszù from Hungary, the nobly rotten grapes are transformed into a paste which is then macerated into fresh juice or fresh dry wine. Depending on how much paste per volume is macerated, the bottled wine has 12% alcohol and sugars between 90 to 180 g/l.
The second most famous sweet wines, those of Germany, is made by stopping fermentation before it runs its full course and keeps residual sugar into the final wine. In such method, the temperature of the fermenting wine is lowered to 4C where the yeast stops functioning. It is then filtered to remove the yeasts and to avoid re-fermentation later. The timing of this method is driven by the level of acidity in the juice for the remaining sugar in the wine will help to balance it beautifully. The interplay of acidity and sugar, as with any sweet wine is key, and these decisions are fundamental not only to how sweet but also how well balanced the final wine will be.
My country of birth, Canada is blessed with the cold weather, and so it is relatively straightforward to obtain frozen grapes healthy enough to produce delightfully pure sweet wines. In this method, grapes are left on the vine well into January when they are harvested at minus 7C. When pressing berries at this temperature, only the very sweet juice that cannot freeze is extracted. Here, it is so sweet that fermentation stops naturally at 10-11% and the remaining wine is lusciously sweet at levels up to 220 g/l. Frozen grapes not only concentrate sugars but they also concentrate acidity and using grapes high in natural acidity like Riesling or Vidal ensures that there is enough to achieve the balance required for high quality and delight.
Drying grapes to concentrate sugars is a technique perfected over centuries in my country of adoption, Italy. In the south of the country, especially in Sicily, grapes are dried for some weeks under the sun on straw mats while in the north, they are dried for months, sometimes up to six, in an especially designed outbuilding, protected from the elements. No matter where the drying period concentrates sugars and acidity, and the skins of the berries desiccate to provides extra complexity reminiscent of raisin, prunes, and dried apricot.
For any of the techniques above, once the sweet wine is obtained, the remaining decision on how to handle it will be similar to that of white wines. The 1st decision concerns whether the wine is handled with or without any oxygen influence to keep freshness with the former or obtain complexing nutty and roasted aromas with the latter. The 2nd decision is whether to use oak for aging the wine for not only that it allows oxygen to influence the wine, but it concentrates the final wine through evaporation in the cellar. If the oak is new, it will provide extra vanilla and spices complexity to the wine.
In the next column, we will discuss the most important faults that we can come across as wine lovers.