Brewers can use various techniques such as the standard reference method (SRM) for example, when evaluating the colour of grains and product. Most techniques used by professional brewers incorporate spectrophotometers to judge the colour of their products while amateurs can use less complex colour scales such as Degrees Lovibond to determine their products colour. In the case of SRM, pale lagers typically are given a value of 2 and the scale can range as high as 700 for dark malt products.
Barley is the classic ingredient used in brewing. Malted barley (Barley grain that has undergone controlled germination) has significantly positive enzymatic properties vs. ingeminated barley depending on the temperature which it is fermented. For example, malted barley has increased amylase activity, which is desirable in fermentation as it provides yeast with a starch energy source. Controlling the fermentation process and selection of the grain can dramatically change the colour of the overall beer product.
Dark Crystal Malts
Dark malts use dark malt grains that have undergone extensive modifications. The color of the malt, in this case dark may also indicate the flavors and bitterness that will be present in the finished beer product. For example bitterness decreases as malt content increases. Dark malts are steeped at a degree of 44-47 and are dried at a temperature of 22°-22°C. They are then stored in a moist warm environment. The grains are then subjected to extensive enzyme activity. The grains are kilned at high temperatures, as high as 200°C where the approach a point of carbonising. After the grain has been exposed to temperatures of 105-110°C, the mailliard reaction becomes apparent. This gives the grain and product a dark appearance. Due to the high Killen temperatures which dark malts endure, enzyme activity ceases after the kilen processing. These high temperatures also give dark malt products signature colors and flavors. Depending on the quantities used, dark malts can be used to darken the color of beers and other products that may need darkening. In terms of flavor, the mailliard reaction can produce slightly sweet tastes in beer products. Dark malts can also provide a finished product with a slightly charred caramel taste. Dark malts also yield higher protein contents (~12%) then lighter beers which may also contribute to taste
Pale Crystal Malt
Pale malts, as the name suggests use a malt grain pale in colour. The key objective when formulating pale malts is to retain adequate brewing enzyme concentration. This is achieved by steeping at a degree of 40-44 and drying the grain quickly at relatively low temperatures (17°-18°C) the most common pale malts used, are kilned at 90°-110°C. These temperatures do not destroy the grains brewing enzymes. Due to pale malts popularity, it is often used as base malt; this means that it composes a large portion of the grist in many beers. The pale malting process is classified as limited modification process that inactivates enzymes and gives the final product a protein content of ~9%.
References:
Bamforth, C. W., & Barclay, A. H. P. (1993). Malting technology and the uses of malt. In A. W. MacGregor & R. S. Bhatty (Eds.), Barley chemistry and technology, AACC Press.
Coghe, S., Gheeraert, B., Michiels, A., & Delvaux, F. R. (2006). Development of Maillard reaction related characteristics during malt roasting. Journal of the Institute of Brewing, 112, 148–156.
Forster, C., Narziss, L., & Back, W. (1998). Investigations of flavour and flavour stability of dark beers brewed with different kind of special malts. Tech. Q. Master Brewers Association of the Americas, 35
T.H Shellhammer (2009). Beer-A Quality Perspective. USA: Academic Press. p213-227
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