Other meanings of gravity
Beverages
In brewing and winemaking, gravity refers to the density of a liquid relative to water, used to measure the concentration of fermentable sugars and predict the potential alcohol content of the finished beverage. It is a fundamental concept in the production of beer, wine, cider, and mead, guiding brewers in recipe formulation and fermentation monitoring.
Gravity is the ratio of the density of a liquid to the density of water, typically measured at a standard temperature (often 20°C or 60°F). In brewing, it is used to estimate the amount of dissolved sugars in the wort before fermentation (original gravity, OG) and after fermentation (final gravity, FG). The difference between OG and FG, multiplied by a factor (often 131.25), gives an approximate alcohol by volume (ABV).
Measurement is commonly done with a hydrometer, which floats higher in denser liquids. More precise instruments include refractometers and digital density meters. Specific gravity is dimensionless, but brewers often use the term "points" (e.g., 1.050 is 50 points).
Original gravity indicates the potential alcohol and body of the beverage. High-gravity worts (e.g., 1.080+) produce stronger beers, while low-gravity worts (e.g., 1.030) yield lighter session beers. In winemaking, grape must gravity correlates with sugar content and potential alcohol; chaptalization (adding sugar) is sometimes used to increase gravity.1
Final gravity indicates the remaining unfermented sugars, affecting sweetness and mouthfeel. A beer with FG above 1.010 may taste sweet, while dry beers finish near 1.000 or below. Monitoring gravity during fermentation helps track yeast activity and determine completion.
Specific gravity (SG) is the most common. Original gravity (OG) and final gravity (FG) are specific points. Apparent attenuation is the percentage of sugars consumed, calculated from OG and FG. Real attenuation accounts for the alcohol's effect on density and is measured by distilling off alcohol. Plato and Brix scales are alternative measures of sugar concentration, often used in professional brewing and winemaking.2
Gravity readings are temperature-dependent; hydrometers are calibrated for a specific temperature, and corrections are needed otherwise. In the 19th century, the British excise used gravity to tax beer, leading to the development of the hydrometer by John Richardson and others. High-gravity brewing is a technique where a concentrated wort is fermented and then diluted with water, increasing brewery efficiency. Some historical beers, like the Scottish "wee heavy," had very high original gravities. In mead making, gravity can be used to calculate the potential sweetness, and some meads are fermented to dryness with FG below 1.000 due to the presence of alcohol.
Gravity is a key metric in the production of alcoholic beverages, influencing both the brewing process and the final product's character.
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