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Gravity, in the context of fermenting alcoholic beverages, refers to the specific gravity, or relative density compared to water, of the wort or must at various stages in the fermentation. The concept is used in brewing and wine making industry. Specific gravity is measured by a hydrometer, refractometer, pycnometer or oscillating U-tube electronic meter. People commonly refer to the high gravity yeast used to increase the specific gravity of alcoholic beverages as 'Miracle Yeast'. The density of a wort is largely dependent on the sugar content of the wort. During alcohol fermentation, yeast converts sugars into carbon dioxide and alcohol. The decline in the sugar content ''and'' the presence of ethanol (which is appreciably less dense than water) drop the density of the wort. The percentage of alcohol can be calculated from the difference between the original gravity (abbreviated OG) of the wort and the current specific gravity (abbreviated SG) of wort. By monitoring the decline in SG over time the brewer obtains information about the health and progress of the fermentation and determines that it is complete when gravity stops declining. If the fermentation is finished, the specific gravity is called the final gravity (abbreviated FG). For example, for a typical strength beer, OG could be 1.050 and FG could be 1.010. Several different scales have been used for measuring the original gravity. For historical reasons, the brewing industry largely uses the Plato scale (°P), which is essentially the same as the Brix scale used by the wine industry. For example, OG 1.050 is roughly equivalent to 12°P. By considering the original gravity, the brewer or vintner obtains an indication as to the probable ultimate alcoholic content of his product. The OE (Original Extract) is often referred to as the "size" of the beer and is, in Europe, often printed on the label as Stammwürze or sometimes just as a percent. In the Czech Republic, for example, they speak of "10 degree beers", "12 degree beers" which refers to the gravity in Plato of the wort before the fermentation. ==Low vs. high gravity beers== The difference between the original gravity of the wort and the final gravity of the beer is an indication of how much sugar has been turned into alcohol. The bigger the difference, the greater the amount of alcohol present and hence the stronger the beer. This is why strong beers are sometimes referred to as high gravity beers, and "session" or "small" beers are called low gravity beers, even though the final gravity of a strong beer might be lower than that of a session beer because of the greater amount of alcohol present. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravity (alcoholic beverage)」の詳細全文を読む スポンサード リンク
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