Beer measurement
The principal factors that characterize beer are bitterness, the variety of flavours present in the beverage and their intensity, alcohol content, and colour.
"Degrees Lovibond" or "°L" scale is a measure of the colour of a substance, usually beer, whiskey, or sugar solutions.
The determination of the degrees Lovibond takes place by comparing the colour of the substance to a series of amber to brown glass slides, usually by a colorimeter.
The Standard Reference Method or SRM[2] is a system modern brewers use to measure colour intensity, roughly darkness, of a beer or wort.
In practice the most common method used to estimate the strength of a beer is to measure the amount of sugars or "extract" in the wort before fermentation and then again once the fermentation is completed, and to use these two data points in an empirical formula which estimates the alcohol content or strength of the beer.
A basic formula[4] to calculate beer strength based on the difference between the original and final SG is:
The formula below[5] is an alternate equation which provides more accurate estimates at higher alcohol percentages (it is typically used for beers above 6 or 7%).
The OE is often referred to as the "size" of the beer and is, in Germany, often printed on the label as Stammwürze [de] or sometimes just as a percent.
[6] The actual measurement was by saccharometer (i.e. hydrometer) correcting for temperature by a calibration scale or else by a special brewer's slide rule.
A much more accurate conversion (with a mean average error less than 0.02°P) can be made using the following formula:[9] where the specific gravity is to be measured at a temperature of T = 20 °C.
The equivalent relation giving SG at 20 °C for a given °P is: Winemakers, as well as the sugar and juice industry, typically use degrees Brix.
Some sources suggest that the origin of the mark was in the breweries of medieval monasteries, where the cross served as a guarantee of quality for beers of increasing strength.
[10] Another explanation for the saltire marks may be rooted in the duty taxes of alcoholic beverages beginning in England in 1643.
Later, brewers added additional (superfluous numeral) X marks to signify progressively stronger beers: "the present quack-like denominations of XX [twenty, but often pronounced "double (letter) X"] and XXX [thirty, often pronounced "treble (letter) X"], which appear, unnecessarily, on the casks and in the accounts of the strong-ale brewers".
During the brewing process, humulone undergoes isomerization to form both cis- and trans- isohumulone which are responsible for the bitter taste of the beer.
[13] Such varieties include Chinook, Galena, Horizon, Tomahawk, and Warrior hops, and these contain alpha acid concentrations up to 16% by mass.
This technique was adopted at the same time as another method based on measuring the concentration (in milligrams per litre; parts per million w/v) of isomerized α acids (IAA) in a beer, causing some confusion among small-scale brewers.
[20]Additionally, HPLC, mass spectrometry, and fluorescence spectroscopy can be employed to measure the amount of iso-alpha acids in a beer.
[27] For high throughput applications (as in quality control labs of large breweries for example), automated systems are available.
[30] Automated systems exist to determine the lag time of beer related to the antioxidant capacity to resist oxidative spoilage of flavours.
[31] Software tools are available to brewers to formulate and adapt recipes with a view to accurately measure the various values in brewing.
