Lesson 5 - The Mashing Process SAQ

*** Your boss has read online that Brut IPA is the next big thing and that it must have a very low final gravity to be any good. They ask you to produce a prototype of around 6% abv with the ‘world’s lowest final gravity’ for tasting.

a)    Considering the mashing raw materials, parameters, and method, how would you design a mashing process to achieve this?

b)    How could you quickly evaluate the success of a trial of your process to achieve the ‘world’s lowest final gravity’? Why must you exercise caution when drawing conclusions from this?

Response:

a)

Raw materials

We need a wort which is very high in fermentable sugars. Adjuncts contain a higher proportion of starch than malt, so a high percentage of adjuncts would be required. If we rely on malt enzymes alone, we need to limit this to 30% of the grist, but if using exogenous enzymes, we could make the adjuncts the highest proportion of the grist. Of all the solid adjuncts, rice grits have the highest proportion of carbohydrates, so they are the best option. The malt used should be well modified, and if we are not adding exogenous enzymes to the main mash, we would need a high diastatic power. The highly modified malt would have higher soluble nitrogen and have the starch granules nicely exposed for conversion. The β-glucan would be degraded to a greater extent than in under-modified malt, allowing us to degrade it further easily in mashing to increase the amount of fermentable material. An over-modified malt would not be beneficial as they tend to be lower in starch as germination has proceeded further. All goods added to the mash should be reduced to the minimum particle size in milling to maximise our access to the starch.

Mashing process

The use of rice grits means we will need to use a cereal cooker to gelatinise its starch before we combine it with the main mash for saccharification. Heat stable exogenous α-amylase and limit dextrinase could be used in the cereal cooker to provide the perfect substrate for β-amylase in the main mash.

For the main mash, we would need a long cytolytic stand at 35℃ to enable us to saccharify as much of the pentosans and β-glucans as possible. We could also opt for a maltase-style mash where we mash in part of the grist at 62°C, before cooling the mash to 35℃ for a cytolysis stand with the rest of the grist and cold water. This would allow β-glucan solubilase to free up the chains of β-glucose residues for hydrolysis in the 35℃ stand. However, this would increase the glucose level in the wort, which risks incomplete fermentation, so the risks probably outweigh the benefits.

There are two ways of looking at the breakdown of the proteins. One is that as we are using a well-modified malt, the protein matrix has been degraded, so access to the starch granules will not be affected. Also, we need to maximise higher molecular weight nitrogenous material to ensure foam stability and to provide some palate fullness in the absence of residual carbohydrates.

The other way of looking at it is that we need to get as much FAN as possible from the malt to ensure there is enough for the yeast, given that we are diluting FAN with a high proportion of adjuncts. We can overcome low FAN by using yeast food, so the best option would be to leave out a proteolytic stand and jump straight to saccharification.

The saccharification stand should be very long at 63℃ to maximise β-amylase activity while maintaining the limit of dextrinase close to its optimum. This should help ensure all liquefied starch is converted to fermentable sugars. The malt enzymes are diluted by the adjuncts, so they are limited in concentration, and as the mash proceeds, the wort will become increasingly concentrated in sugars that inhibit their activity.

A thinner mash would also promote the production of fermentable sugars. Adding exogenous β-amylase, α-amylase, limit dextrinase enzymes would, of course, speed things up and guarantee a greater degree of saccharification (as long as their temperature optima matched the malt equivalent).

At the end of the saccharification stand, a slow ramp up to 67℃ would allow malt α-amylase to start to work close to its optimum, maintaining some β-amylase activity.

If relying on malt enzymes alone, a pH of 5.5 to favour malt limit dextrinase and β-amylase would help ensure greater fermentability. We could acidify the mash down to 5.2 at the end of saccharification, so we don’t lose the benefits of a lower pH in the rest of the process.

As long as the mash was thin enough to pump, we could leave out an increase in temperature before mashing off to extend conversion into wort separation.

Wort composition

As well as ensuring the fermentable sugar level is as high as possible, we need to ensure there are adequate yeast nutrients to sustain the yeast as it ferments. We have opted for a high adjunct rate, so will need a yeast food with yeast cofactors, vitamins, and FAN to help ensure that all the fermentable material is attenuated.

b)

The quick test we could use to see if our prototype wort is going to make the boss happy is the wort attenuation limit (WAL) test. In a WAL test, wort is added to a flask with 7.5 g/100 mL of compressed yeast. The flask containing the wort and yeast is then kept warm in an incubator at maintained at 25℃ and shaken to enable the yeast to consume all the sugar in the wort. The test is complete when the gravity stops falling. We could calculate the percentage fermentability from the OG and PG from this test. We would need to be cautious about the results in this test as the yeast is added in excess of the amount required to fully ferment the beer (several times more than we would add to a fermentation vessel). This means any lack of nutrients in the wort is unlikely to affect the test, and the WAL gravity will be lower than we can achieve in the brewery.