What component primarily determines the sugar content of grape juice?

The component that primarily determines the sugar content of grape juice is the type of grape used. Different grape varieties inherently possess varying sugar levels, which are influenced by factors such as the grape's genetic makeup, the climate in which they are grown, and the conditions of the vineyard. Some grape varieties, such as Cabernet Sauvignon or Zinfandel, are known for producing higher sugar levels compared to others.

Must weight, which measures the density of the grape juice and reflects its sugar concentration, indeed gives an indication of the sugar content. However, it is a result of the natural sugars present in the grapes rather than a determinant in itself. Acidity levels can affect the taste and balance of the wine but do not dictate sugar content directly. Likewise, fermentation temperature plays a role in how yeast ferments sugar into alcohol but does not influence the initial sugar content found in the grapes.

Thus, understanding that the sugar content is primarily influenced by the grape variety provides insight into the winemaking process and the significance of selecting specific grapes for desired wine styles.