Lesson 3 - Mashing Biochemistry SAQ

**/*** A colleague says, ‘We don’t need malt to meet our specification for β-glucan level and protein modification. We can just adjust the mashing process.’ Are they correct? Explain your reasoning.

Response

This statement relates to two substrates and the capacity of enzymes in the mash to catalyse their degradation. If both of these substrates are plentiful in the malt, our ability to access the barley starch granules will be limited. If we are able to achieve a limited level of degradation and dissolution, this could lead to a viscous mash. In addition, unless degraded extensively in mashing, they will go on to cause problems with hazes and filtration throughout the brewing process. So, we are considering if it is practical to break down significant quantities of barley storage protein and β-glucans during mashing or if we need this to be completed as part of the malting process. We can evaluate this question by considering the enzymes that are used either by the barley grain or during the mashing process to break down these substrates.

Proteases undertake the catalysis of the breakdown of barley storage proteins. We group these enzymes into three groups, endoproteases, carboxypeptidases and aminopeptidases; each has a role in reducing these proteins in size and producing FAN and larger peptides. Compared to α-amylase, they are all heat labile and operate optimally around 40-45°C. We can incorporate a temperature stand dedicated to enabling them to act on the protein molecules, so things are looking promising for our colleague. Unfortunately, two factors count against this being successful. The first is that the solubility of undegraded proteins is likely to be poorer than those extensively broken down in malting, so our enzymes will have slow and limited access to their substrates. The second is that being heat labile, the quantity of enzymes remaining after kilning is likely to be significantly lower than that available during germination. We can, of course, increase the length of the stand, but in brewing, time is money, so we would need to evaluate if the extended mashing time is justified by our savings on the malt.

The β-glucans in the malt are degraded by the combined action of the endo β-(1,4) glucanase, endo β-(1,3) glucanase, barley β-glucanase and β-glucan solubilase enzymes. Endo β-(1,4) glucanase and barley β-glucanase are highly heat labile so are present in malt in a fraction of the quantity available during germination. Endo β-(1,3) glucanase is relatively heat stable, but its action on β-glucans is limited to catalysing the hydrolysis of β-glucan chains with sequences of consecutive (1,3)-β-bonds, so it doesn’t do much! We could incorporate a 40°C β-glucan stand into our mashing programme to allow the heat labile enzymes to operate, but this is unlikely to be effective. The main reason for this is that β-glucan solubilase doesn’t really get going at 40°C, so it will not release sufficient strands of glucose residues from their protein crosslinks to allow sufficient hydrolysis. When we heat the mash to the next stand, β-glucan solubilase will kick in, but the heat labile endo β-(1,4) glucanase and barley β-glucanase will be well on the way to being denatured. We will have increased wort viscosity and further problems down the line but due to β-glucan in solution.

So, our colleague is a fool, and we should tell them so! Well, maybe not. With heat-stable exogenous enzymes, we do have the ability to process malt with higher levels of protein and β-glucan without the need for extended low-temperature stands, so it is actually achievable. As it stands, there is not an enzyme product that will guarantee to do the job perfectly, and we may get proteolysis that we don’t want and produce beer with poorer foam stability and a thinner body. There is also the question of cost. Does the commercial enzyme product cost less than the saving we have made on the malt? If not, then it’s a bad idea.

We should also consider the other aspects of the brewhouse process. If the malt is significantly under modified and high in β-glucans, it is likely to be poorly friable, so unless our mill is designed to handle under modified grain (six-roll or hammer), we will not be able to comminute it effectively, so have no hope during mashing. So, if this is the case, our colleague is definitely wrong.