Lesson 2 - Mashing Biochemistry
This lesson deals with the biochemical aspects of mashing. We will meet the main substrates and the enzymes that break them down. We will learn what enzymes are, how they operate and how they are affected by the environment of the mash. Finally, we will cover how starch is gelatinised, liquefied and saccharified to make a wort with the desired sugar spectrum.
NSP Degrading Enzymes
If our malt specification is correct and our malt suppliers have done their job, our next set of enzymes shouldn’t be required in the mash. As a group of enzymes, they are renowned for being the most heat labile.
β-Glucanases
The most significant β-glucanases are the endo-β-glucanases. These catalyse the hydrolysis of susceptible bonds at random. The malt endo-β-(1,3)-glucanase, sometimes called laminarinase, is relatively heat stable but will only catalyse the hydrolysis of β-glucan chains with sequences of consecutive (1,3)- β-bonds. It has been called a weak enzyme because its action in mashing is minor.
Endo- β-(1,4)-glucanase is heat labile and catalyses the hydrolysis of β-(1,4) bonds. A limited amount survives kilning (in the case of very pale malt), and it will degrade β-glucan chains in a 40°C mash.
Barley β-glucanase or to give it its full name endo β-(1,3;1,4)- β-glucan 4-glucanohydrolase, catalyses the hydrolysis of the β-(1,4)-bond adjacent to a β-(1,3)-bond producing oligosaccharides. It is heat labile (optimum temperature 40°C), and a large proportion is denatured during kilning, leaving little to work in the mash.
Pentosan degrading enzymes
There is a higher concentration of arabinose and xylose in solution after mashing than at the start. Therefore, we know that pentosans are broken down, but at present, we don’t know the exact mechanism. Arabinosidase and xylobiase are responsible for the degradation of the pentosans to arabinose and xylose sugars in the malting process. Of the two, xylobiase is the most heat stable, so is a likely candidate for the enzyme working in the mash.
The concentration of arabinose and xylose is higher in mashes with lower temperature stands, so the optimum temperatures of the enzymes responsible are lower than those of the enzymes of starch conversion.