Making sweet wine involves methods that either concentrate the natural sugars in the grapes or interrupt the fermentation process before all the sugar is converted to alcohol. Here are several ways to achieve this, based on common winemaking techniques:
Sweet wine can be made through various techniques that either increase the initial sugar content of the grape must or stop fermentation early, leaving residual sugar behind.
Methods for Producing Sweet Wine
Several distinct approaches are used globally to craft sweet wines, each resulting in unique styles and flavors.
1. Concentrating Sugars Before Fermentation
These methods focus on increasing the sugar level in the grape juice before fermentation begins, providing more sugar than the yeast can typically consume.
- Drying the Grapes: One effective way to concentrate the sugars in grapes is by allowing the fruit to dry, either on the vine, on mats, or by hanging them. This process, known as passerillage in French or passito in Italian, causes water to evaporate, leaving behind a higher concentration of sugars, acids, and flavor compounds in the remaining juice.
- Using Noble Rot: A beneficial fungus called Botrytis cinerea (noble rot) can dehydrate grapes under specific humid conditions followed by dry periods. The fungus pierces the grape skin, allowing water to evaporate while concentrating sugars and adding unique honeyed and ginger notes to the resulting wine. This is the key behind famous wines like Sauternes and Tokaji.
- Freezing the Grapes: Grapes left on the vine until temperatures drop below freezing can be harvested and pressed while still frozen. Since water freezes but sugar does not, pressing frozen grapes extracts a highly concentrated, sugary must, leaving the ice crystals behind. This method is used to make Ice Wine (Eiswein).
2. Stopping Fermentation Early
Fermentation is the process where yeast converts sugar into alcohol and carbon dioxide. Stopping this process prematurely leaves unfermented sugar (residual sugar) in the wine, making it sweet.
- Removing Yeast by Filtering: Winemakers can stop fermentation by filtering out the yeast cells from the wine. This physical removal prevents further conversion of sugar into alcohol, leaving the desired level of sweetness. This is often used for lighter, fruitier sweet wines.
- Removing Yeast by Fortifying: Fortification involves adding a high-proof neutral grape spirit (like brandy) to the fermenting must. Yeast is highly sensitive to alcohol; adding spirit increases the alcohol level rapidly, killing the yeast and stopping fermentation. This leaves significant residual sugar and results in higher-alcohol sweet wines like Port or Sherry (though many Sherries are dry, the sweet versions use this method or blending).
- Blending with a Sweet Liquid: Another method is to ferment a wine to dryness (meaning all or most sugar is converted to alcohol) and then blend it with a sweet liquid. This liquid could be unfermented grape juice (known as Süssreserve in German winemaking) or a sweeter wine. This allows for precise control over the final sweetness level.
These techniques require careful vineyard management and precise control in the winery to balance sweetness with acidity and other flavor components, resulting in delicious and complex sweet wines.
