2.17 How Can I Estimate When to Fortify a Fermenting Juice to Achieve Desired Sugar and Alcohol Concentrations?

Fortified wines, such as Port-style wines, can be made by choosing to ferment the juice or must to a desired sugar concentration and then adding a sufficient amount of a distilled spirit to arrest the fermentation and raise the alcohol to a predetermined level. In order to carry this out, we have to know the amount of sugar left in the juice at anyone moment in time. In small wineries, a hydrometer is often used for this purpose, because it gives an instant answer and is economical to buy. However, using a hydrometer to estimate sugar concentration is complicated by the presence of alcohol in the juice and causes the hydrometer to sink more, thus indicating a lower Brix than is actually present. One percent v/v alcohol obscures 0.47 Brix ( Rankine, 1991). The true Brix is given by: