HULK MASH!

Modified From: http://beforeitsnews.com/motor-junkies/2013/04/hulk-smash-2463796.html

Who knows, the big green wrecking machine may also be an avid homebrewer when he hangs up his purple shorts and returns to being Bruce Banner the mild mannered scientist. Most everyone is familiar with the basic principles of how beer, and for that matter all alcoholic beverages are made; you take some variation of a sugar solution, add yeast and let the magic happen. In the case of beer and malt-liquor, you have a sugar solution made primary up of maltose; but where does this maltose come from exactly?

Well as the name implies, from malt! More specifically, malted barley, wheat, rye, or other cereals. The only trick is that this maltose is locked away inside the grain as large polysaccharide (sugar) chains that cannot be broken down by yeast alone. This is where the mashing process comes into play. Typically, when you get grain from your LHBS it has already been malted (basically controlled germination). It may have also been roasted or kilned, creating malts of various flavor and color. In simple terms, the malting process activates the production of certain enzymes in the seed to mobilize sugars it requires for growth into a new plant. This process is then halted by drying; stopping the enzymatic breakdown of the starch but preserving the enzymes.

 Figure 1. Crystaline structure of α-amylase (left) and β-amylase (right) (wikipedia.org)

The enzyme that we as brewers are mostly concerned with is amylase. In general, amylase catabolizes (the metabolic breakdown of complex molecules resulting in simpler molecules and energy) larger polysaccharide chains resulting in smaller chains, some of which can be used by yeast to make alcohol and CO₂. Amylase catalyzes the hydrolysis (chemical breakdown with the addition of water) of the polysaccharides amalose and amylopectin, the two molecules that make up starch into smaller oligosaccharides. There are two types of amylase, α-amylase and β-amylase that have several key differences (Figure 1). α-amylase cuts at random α-1,4-glycosidic bonds, making it relatively fast, cleaving amalose into both maltriose and maltose and amylopectin into glucose and "limit dextrin" at branch points (Figure 2). This results in the production of some longer unfermentable sugars that can be cleaved further given enough time and high enough α-amylase concentrations ⁽¹⁾.

Figure 2.  α-amylase (Hulk) action on a starch

β-amylase also works on α-1,4-glycosidic bonds, but only on the non-reducing end of the polysaccharide chain, making it slower, cleaving two glucoses off at a time resulting in a single maltose molecule⁽²⁾ (Figure 3).

Figure 3. β-amylase (Red Hulk) action on starch

Figure 4. Products of hydrolyzation (Left to Right) Glucose, Maltose, Maltotriose, Limit Dextrin (wikipedia.org)

The activity of these enzymes can be controlled by the temperature of the mash.  α-amylase has a temperature optimum from 149 °F to 158 °F ⁽³⁾ and β-amylase from 134 °F to 141 °F ⁽⁴⁾. By controlling the mash temperature you can push the optimal temperature to α-amylase or β-amylase which will result in more or less body respectively in the final product .

Only certain grains have still have enough amylase to convert the starches to fermentable sugars. Typically, this includes grains that have not been extensively roasted or kilned as these processes denature the amylase enzymes. This difference in amylase enzyme is measured in diastatic power. The greater the diastatic power the more amylase present and the greater ability to convert available starches. American 2-Row, American 6-Row, and Maris Otter are examples of "base malts" with relatively high diastatic power (140, 160, and 120 respectively) and are able to convert about an equal amount of malt with no diastatic power. Munich malts do still have diastatic power (72) but it is much lower than that of the base malts. Kilned malts like black malt have no diastatic power. Other partially processed adjuncts like flaked oats and wheat do have starches available for conversion but no diastatic power and must be mashed with base malts to extract the sugars from the grain.

If you're wanting to venture into brewing beers with a more complex grain bill than the typical extract recipe or just want to have more control of what exactly is going into your wort remember the words of the mighty Hulk, "HULK SMASH!".

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1. Greenwood, C.T., MacGregor, D.Sc., and MacGregor, A.W. 1965. The isolation of α-amylase from barley and malted barley, and a study of the properties and action-patterns of the enzymes. J. Inst. Brew. 71:405-417
2. Enevoldsen, B.S., Bathgate, G.N. 1969. Structural analysis of wort dextrins by means of β-amylase and the debranching enzyme, pullulanase.J. Inst. Brew. 75:433-443
3. Bertoft, E., Andtfolk, C., and Kulp S.E. 1984. Effect of pH, temperature, and calcium ions on barley malt α-amylase isoenzymes. J.Inst. Brew. 90:298-302
4. Eglinton, J.K., Langridge, P., Evans, D.E. 1998. Thermostability variation in alleles of barley beta-amylase. J Cereal Science 23(3): 301-309