Monitoring fermentation

Progress of a fermentation can be monitored in several ways. The most obvious is by simply observing activity in the fermentation vessel. As long as carbon dioxide is vigorously given off, the yeast are still working. Laboratory fermentations are sometimes followed by weighing the fermentation vessel at frequent intervals, thus obtaining a record of the weight of carbon dioxide gas lost and therefore, by calculation, the amount of sugar remaining. Chemical analyses of the unfermented sugar remaining, or of the alcohol produced, are accurate measures of the course of fermentation but are seldom used as they are complex and time consuming. The technique most commonly used in the operating cellar is a measurement of the density of a sample of fermenting juice.