The color of beer is affected by the complex mix of compounds in a beer. These absorb light over a range of wavelengths, therefore, absorption balance of color varies greatly between beers. For example, Stouts may contain coloring compounds absent from lighter beers, even if a Stout is diluted to the same color level as a Lager the absorbance spectrum is different.
This makes measurement of color intensity difficult. Beer color can be measured by standard scales of color units—Lovibond, SRM, or EBC. In addition to light and dark, beer may also vary in its hue from reddish to yellowish.
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.
EUROPEAN BREWERY CONVENTION (EBC)
THE EBC COLOUR SCALE WAS DEVELOPED BY THE INSTITUTE OF BREWING AND THE EUROPEAN BREWING CONVENTION.
The EBC is a recognised method for colour grading of beers, malts and caramel solutions as well as similarly coloured 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.
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.
EBC → SRM
EBC × 0.508 = SRM
SRM → EBC
SRM × 1.97 = EBC
°L → SRM
(1.3546 × °L) – 0.76 = SRM
SRM → °L
(SRM + 0.76) ÷ 1.3546 = °L