Yeast is a type of fungus that exists in various forms, but the most commonly used species for winemaking is Saccharomyces cerevisiae. This particular strain of yeast has been selected over centuries for its ability to efficiently convert sugar into alcohol and handle the specific conditions required for winemaking.
The first step in making sweet wine is selecting the right grapes. While most grapes contain natural sugars, some varieties have higher sugar levels, making them more suitable for the production of sweet wines. These grapes often have thick skins, which allows for greater sugar concentration as the grapes ripen on the vine.
Once the grapes have been harvested, they are crushed to release the juice inside. This juice, known as “must,” contains the sugars that will be transformed into alcohol. Additionally, during the crushing process, the grape skins, seeds, and stems can also contribute to the flavors and tannins present in the final wine.
After the crushing, the must is transferred to a fermentation vessel, typically a stainless steel tank or oak barrel. At this stage, winemakers add yeast to the must, initiating the fermentation process. Yeast consumes the sugars in the must, breaking them down into alcohol and carbon dioxide. The byproduct of this process is heat, which raises the temperature of the fermentation vessel.
To make sweet wine, winemakers employ a technique called arrested fermentation. This means that the fermentation process is halted before all the sugar has been converted into alcohol. By stopping fermentation at a specific point, winemakers can preserve a portion of the grape’s natural sweetness.
To achieve arrested fermentation, winemakers either monitor the sugar levels in the fermenting must or add a high-proof alcohol, such as brandy, to increase the alcohol concentration. This extra alcohol kills off the yeast, preventing further fermentation and preserving the residual sugar in the wine.
The amount of sugar left behind in the wine will determine its sweetness level. There are different categories of sweet wines, ranging from off-dry or semi-sweet to dessert wines, which are often very sweet. The sweetness level can be influenced not only by the winemaker’s intervention but also by the ripeness of the grapes and the sugar concentration in the must.
In conclusion, the production of sweet wine heavily relies on the presence of yeast during the fermentation process. Yeast converts the sugars in grape juice into alcohol, with the fermentation process being controlled to preserve a portion of the grape’s natural sweetness. This essential microorganism allows winemakers to create a wide range of sweet wines, each with its unique and distinct flavors. So, the next time you indulge in a glass of sweet wine, remember that it is the result of the magical transformation brought about by yeast.