The analysis of beer for alcohol content is an important part of brewing laboratory work both for quality assurance programs and for legal reporting purposes. Once alcohol is produced in beer, brewers need to measure it. See aging of beer and ethanol- tolerant yeast strains. For normal worts and fermentations, alcoholic strength in beer tops out at about 15% ABV, with these beers normally requiring long aging before they become palatable. In this, they can come to resemble laboratory experiments rather than beers, although some very interesting beers have been produced in this manner. Although it is possible to coax beer fermentations to produce beers with more than 20% ABV, these generally require special yeast strains and techniques. There are many beers on the market with only 3.5% ABV or below, whereas some beer styles, such as barley wine, commonly reach 12% ABV. However, the range of strength in beer is far wider than that of wine. The average strength of beer is between 4.8% and 5.2% alcohol by volume (ABV).
These above values can be used together with equations known to the brewer and brewing chemist to determine the actual exact alcohol strength. The original gravity minus the final gravity (real extract or true final gravity) will produce a value that indicates the amount of fermentable sugars consumed this, in turn, indicates the amount of alcohol produced (see below). See real degree of fermentation (rdf) and real extract. These will be left behind and provide the beer with body and sometimes sweetness.
Not all sugars in the wort will be fermented because wort contains non-fermentable elements, particularly complex sugars. The real degree of fermentation is a measurement of the percentage of the original gravity that was actually fermented, adjusted once again for alcohol content. The real extract then represents the true final extract (containing residual sugars and dextrins-more complex carbohydrates, some protein, and the mineral content of the sample) in the beer expressed as grams/100 grams (or percentage terms). The real extract (the gravity value not compromised or “obscured” by alcohol) is an important value and can be computed or determined following the careful removal of alcohol from a known amount of the wort/beer. There is a drop in gravity caused by the conversion of the sugars to alcohol, but the gravity also drops because the newly generated alcohol is lighter than water. However, as sugars are consumed the alcohol content rises and the “extract” in the beer is not read correctly and is regarded as the apparent value (apparent extract). The brewer monitors the progress of fermentation by following the changing SG (or Plato) value until it reaches a terminal value (the maximum degree of fermentation). See balling scale, hydrometer, plato gravity scale, and specific gravity.Īs fermentation continues, the sugars in the extract are consumed and the SG of the liquid drops. In the brewing industry this measurement is denoted in degrees Plato (°P) and winemakers refer to it as degrees Brix. This number is equivalent to a percentage weight/weight. Brewers and winemakers take this as an expression of the sugar content in units of grams of sugar per 100 g of wort.
In the brewery this is often measured using a hydrometer.
The initial original gravity of wort is a measure of the specific gravity (SG) of the wort at 20☌ (where, simplified, water at a standard reference temperature has an SG of 1.0000) and is also known as the original extract. Alcoholic Strength And Measurement in beer is generated as a function of both the quantity of fermentable sugars originally present in beer wort and the extent to which those sugars are actually fermented by yeast.