This is a single value of lightness/darkness taken by putting a sample of beer into a spectrophotometer and reading the amount of absorption at a particular blue wavelength that is readily absorbed by beer.
In the nineteenth century, Joseph Lovibond devised the first beer color scale using a series of colored glass disks. When the spectrophotometric method replaced the earlier method, it was found that the numbers matched up fairly closely with Lovibond’s, so sometimes you still see beer and malt color described in degrees Lovibond U.S. and European standards differ by the thickness of the cuvette used to hold the sample beer ̶ ½ inch in the U.S. Standard Reference Method (SRM), and 1 centimeter for the European Brewery Convention (RBC). Because of this, the same beer measured by the EBC method will have a number almost exactly twice as high as the SRM. In addition to light and dark, beer may vary in its hue from reddish to yellowish. Methods using multiple colors, called tristimulus, can be used to measure beer in a way that matches more closely what the eye sees, but these are rarely used.
STANDARD REFERENCE METHOD (SRM)
STANDARD REFERENCE METHOD OR SRM IS A SYSTEM MODERN BREWERS USE TO MEASURE COLOR INTENSITY, ROUGHLY DARKNESS, OF A BEER OR MALTED GRAIN.
This method involves the use of spectrophotometry to assign a number of degrees SRM to light intensity. The SRM number is defined as 10 times the absorbance of a sample at 430 nanometers measured through a .5-inch cell. The 430-nanometer wavelength corresponds to a deep blue light, and is the wavelength at which beers appear most different from each other.
The standard was adopted in 1950 by the American Society of Brewing Chemists as an objective measurement of color unburdened by the difficulties of the Lovibond system; the measurement of the color of a beer in degrees SRM and degrees Lovibond are approximately equal and in practice can be used interchangeably to evaluate the color of intensity of beer.
The BU scale is the measurement of the bitterness of a beer. Starting at zero, the scale is unrestricted, but generally beers don’t stray higher than 100 BUs. Anything above this is likely to be too bitter for most of us to taste much difference, and is certainly an acquired taste.
There is a European version (EBU) of the measurement that gives very slightly different numbers. but for the most part these systems can be thought of as the same. Most home brewers and small-scale brewers use a calculated BU number, which may vary considerably from measured numbers. depending on a large number of factors, especially at the higher end for super-hoppy beers like double IPAs and their ilk (greater than 80 BU or so), there is some doubt as to the reliability of the standard assays.
EUROPEAN BREWERY CONVENTION (EBC)
THE EBC COLOR SCALE WAS DEVELOPED BY THE INSTITUTE OF BREWING AND THE EUROPEAN BREWING CONVENTION.
The EBC is a recognized method for color grading of beers, malts and caramel solutions as well as similarly colored liquids. It has a range of 2 to 27 visual units; yellower pale worts and lagers at the low end of the scale and the amber of dark worts, beers and caramels at the upper end of the scale.
European standards differ by the thickness of the cuvette used to hold the sample beer — ½ inch in the U.S. Standard Reference Method (SRM), and 1 centimeter for the European Brewery Convention (EBC).
Because of this, the same beer measured by the EBC method will have a number almost exactly twice as high as the SRM.
DEGREES LOVIBOND (°L)
IN THE NINETEENTH CENTURY, JOSEPH LOVIBOND DEVISED THE FIRST BEER COLORIMETER AND THE COLOR SCALE DEGREES LOVIBOND.
Lovibond came to believe that the color of beer is a quality indicator. He invented an instrument, the Tintometer, to measure the color of transparent liquids, as matched with combinations from three graduated sets of 20 each yellow, red, and blue color filters.
In his first book, Lovibond describes the Tintometer and its uses. The test liquid is placed in a glass cuvette and inserted into the instrument. A series of glass filters can be placed in slots next to it. By visual comparison, looking through the ocular, the color of the test liquid is matched in color appearance against combinations of appropriately selected filters, a task requiring some practical experience. The measured color of the liquid was identified with filter and filter-strength numbers.
JOSEPH WILLIAMS LOVIBOND
Joseph Williams Lovibond, born 17 November 1833 at Long Sutton, Somerset, was the third son of brewer John Locke Lovibond. When he joined the family brewery, around 1854, he found that there was no simple method available for measuring the colour of beer and wort (malt solution).
In 1885 after Joseph introduced the LOVIBOND color scale and the first colorimeter ever, he founded the Tintometer Ltd. Company in Salisbury, England, to manufacture his patented measuring instrument.
Today the company still produces various types of color-measuring instruments.
Methods using multiple colors, called tristimulus, can be used to measure beer in a way that matches more closely what the eye sees, but these are rarely used in brewing.
Tristimulus values may be obtained from measurements made on a tristimulus colorimeter that visually matches a color under standardized conditions against the three primary colors—red, green, and blue; the three results are expressed as X, Y, and Z, respectively.
These must then be normalised to equivalent CIE values and should be properly designated as R, G and B instead of X, Y and Z.