Determining the alcohol content by volume (ABV) from specific gravity readings is a fundamental practice in brewing and winemaking. This calculation relies on the difference between the original gravity (OG), measured before fermentation, and the final gravity (FG), measured after fermentation is complete. The OG indicates the sugar concentration of the unfermented liquid, while the FG reflects the remaining sugar content after the yeast has converted the sugars into alcohol and carbon dioxide. The difference between these two gravity readings is proportional to the amount of alcohol produced.
Accurate determination of alcohol percentage is essential for several reasons. It allows brewers and winemakers to comply with labeling regulations, estimate taxation obligations which are often based on alcohol content, and maintain consistency in product quality. Historically, gravity measurements have been the primary method for estimating alcohol content, providing a reliable and relatively inexpensive alternative to more complex analytical techniques. This method empowers both professional and amateur producers to understand and control their fermentation processes.