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.
Lipases and Lipoxygenases
Our last set of enzymes are ones that we would rather do without. Let’s find out why.
Lipase enzymes are plentiful in malt acrospires. They catalyse the hydrolysis of triglycerides to yield free fatty acids. Esterase enzymes are also involved in the breakdown of triglycerides. Free fatty acids are more soluble in wort than triglycerides and, once in solution, are readily oxidised. This oxidation makes them more polar and hence even more soluble.
Lipoxygenases, often referred to as LOX, catalyse the oxidation of fatty acids to produce hydroxy and hydroperoxyl fatty acids. There are two lipoxygenases found in barley, and these are called LOX-1 and LOX-2. LOX-2 is more heat labile and is denatured during kilning, so only LOX-1 is active in mashing. LOX-1 activity is also enhanced by another more heat stable enzyme related to peroxygenase.
As we discussed earlier, the oxidation of unsaturated fatty acids to aldehydes is important because they are major contributors to stale beer flavour. The reactions that produce the aldehydes from fatty acids are very complex. Minimising oxygen pick up, and the action of LOX in the mash with low pH and high mashing temperature can help to reduce the concentration of their precursors and improve flavour stability.