Lesson 8 - Mashing End of Unit SAQ

*** The temperature sensor in your MCV is reading 5°C lower than the actual temperature. You undertake the mashing programme shown in the table below on under-modified malt using a water to grist ratio of 4.5:1. What will happen in the mash, and how will this affect the wort produced?

Response

Our original mashing profile would have worked reasonably well to process an under-modified malt. Our faulty temperature sensor means that instead of the desired temperature profile, we are now mashing with the profile in the table below.

The water to grist ratio is high at 4.5:1, so the effect of the extra 5°C on the enzymes will be significant as thin mashes offer less protection. To answer the question, we can consider the effects of each stand on the enzymes operating in the mash and the nature of the wort likely to be produced.

47°C stand changing to 52°C

47°C is a relatively high temperature for a β-glucan stand, and the extra 5°C puts it closer to a proteolytic stand. The good news is that the important cytolytic enzymes, pentosanases, barley β-glucanase, and endo-β-(1,4)-glucanase would still be below their inactivation temperatures. The bad news is that the most heat labile of these, endo-β-(1,4)-glucanase, would be out of its optimum range and is already at a low concentration in mashes due to inactivation during kilning. Therefore, it is unlikely to have a significant impact.

Barley β-glucanase is also 12°C above its optimum so that it will be quite limited in its contribution. If the malt is high in β-glucan, which would be expected in an under-modified malt, it is likely that there will not be sufficient enzyme activity to reduce the levels in wort below the point where β-glucan will cause problems with wort separation, filtration and form hazes and precipitates in the finished beer. One thing in our favour is that with a higher temperature, β-glucan solubilase will be slightly more active, so what β-glucanase capacity there is can catalyse the hydrolysis of the hemicellulose chains released.

More good news about this stand is that it is a good temperature for proteolysis. Endoproteases, carboxypeptidases, and aminopeptidases are all just above their optimum bands, so should provide a reasonable break down of remaining barley storage proteins to improve colloidal stability and provide FAN.

55°C stand changing to 60°C

Here we have what was a warmish stand for proteolysis changed to a cool stand for saccharification. The proteolytic enzymes we listed earlier will be well above their optimum temperatures and, by the end of the stand, will have been hotter than they prefer for 85 minutes. This means their effectiveness will be dramatically reduced soon after the temperature has been ramped up, and they will be pretty much inactive by the end.

Proteolysis should still be as successful as the original programme, as the time at a temperature allowing proteolysis to occur should be about the same. The 45 min stand at the optimum temperature for β-glucan solubilase could cause us more β-glucan related problems because now there will be very limited β-glucan hydrolysis occurring.

At 60°C, β-amylase will be operating but at a reduced rate, and barley starch doesn’t gelatinise until above 61°C, so not a lot is going to happen. Some starch chains may have been released during the malting process, but the substrate concentration for β-amylase would be very low.

One bit of good news is that limit dextrinase would be within its optimum range, so it will help provide some more non-reducing ends for β-amylase. The fermentability of the wort will increase markedly during this stand, but the extract recovery would be quite minimal.

65°C stand changing to 70°C

Here we move into conversion and saccharification territory. In the ramp from 60°C to 70°C, the starch will start to gelatinise, and α-amylase will be able to start catalysing the hydrolysis of the starch molecules. During the ramp, ɑ and β-amylase will both be working quite close to their optima, but as the temperature gets close to 70°C, β-amylase and limit dextrinase will be denatured.

Limit dextrinase will be very active at the start of the ramp but denatured by the end. Therefore, when most of the starch is liquefied, there will be no debranching and saccharification by β-amylase will be initially slow and then minimal. With 60 minutes at 70°C, extract recovery should be very good, but in the absence of β-amylase and limit, dextrinase fermentability will be relatively low.

73°C stand changing to 78°C

78℃ is hot enough to denature all the enzymes involved in wort production, so no change in the sugar spectrum or the level of FAN would occur. This stand would be a waste of time and needlessly increases the thermal load on the mash, which could reduce product shelf life.

78°C stand changing to 83°C

This stand is also a waste of energy and could affect flavour stability. Temperatures this high will also increase the number of polyphenols extracted from the malt husk and lipids from the embryo. This could compromise the colloidal stability of the product and lead to a reduction in foam potential and flavour stability.

So, we have a poorly fermentable wort with high viscosity that will be difficult to filter. The excess thermal load may mean the beer goes stale prematurely, and the lipid extracted may cause head retention problems and reduce flavour stability. Although 5°C doesn’t sound a lot, here it is the difference between success and failure. The moral of this story is we need accurate and well-calibrated temperature measuring instruments in the brewhouse to be able to brew the beer we set out to make!