What process is used to fortify Sherry wine?

The process used to fortify Sherry wine involves adding grape spirit, commonly known as brandy, to the wine. This fortification process not only raises the alcohol content of the wine but also stops fermentation, preserving the natural sugars and flavors present in the grapes.

When the grape spirit is added, typically after some fermentation has already occurred, it helps to create the unique profiles associated with different styles of Sherry, such as Fino or Oloroso. The level of fortification and the timing of the addition of the grape spirit ultimately influence the wine's sweetness, flavor, and aging potential.

In contrast, the other options presented do not accurately depict the fortification process specific to Sherry. For instance, adding sugar is often used in many wine styles to increase sweetness, but it does not contribute to fortification. Blending with other wines can change the flavor profile of the final product, but this technique does not increase the alcohol content. Fermenting for longer periods also does not align with the fortification process; while it can affect the wine's characteristics, it does not involve the addition of alcohol. Thus, the fortification of Sherry wine is distinctly characterized by the addition of grape spirit.