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.
Starch
Starch is a carbohydrate that has the chemical formula (C6H10O5)n.
‘n’ represents the number of glucose making up the starch molecule.
Biochemical names for carbohydrates
Throughout this lesson and indeed the rest of the course, we will see a variety of technical-sounding biochemical names for carbohydrates. In science and brewing sometimes several names are used for the same thing, and it can get confusing. Here’s a quick summary of some of them and what they mean.
Saccharide is a word for a sugar that comes from the medieval Latin word for sugar. Monosaccharides are single sugar molecules, and then we move to di- (two molecules), tri- (three molecules), and polysaccharides (many sugars) as the number of sugars in the carbohydrate increases. This medieval Latin word for sugar is also found as part of saccharification and our old friend Saccharomyces. Polysaccharides are polymers (poly meaning many) and the sugar molecules are the monomers forming these polymers. Strictly speaking, any molecule composed of more than one sugar is a polysaccharide, but the term is usually only applied to those that contain more than ten.
The suffix ‘ose’ means sugar, which is helpful until we consider amylose, which isn’t one! Pentoses are five-carbon sugars, and hexoses are six-carbon sugars.
Glucan is a word to describe a polymer formed from monomers of glucose. The word glucose is thought to have been invented by a French professor using the Greek word ‘glykys’, which means sweet.
The prefix ‘gly’ also comes from the Greek word glykys and also refers to glucose, for example, in a glycosidic bond and glycogen (another glucose polymer) but not glycerol which is an alcohol just that happens to taste sweet!
Oligosaccharides are small polysaccharides that typically contain between three and ten monomers.
Starch and β-glucans are common glucan polysaccharides. Dextrins are smaller polysaccharides formed when larger polysaccharides are broken down or when they are being assembled by plants and animals. So, in fact, dextrins can be sugars, oligosaccharides, polysaccharides and even α and β-glucans!
There are two forms of starch. These are:
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Amylose
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Amylopectin
Although they are different forms, that does not mean they exist separately (apart from in chemistry labs). All starch in nature contains both.
As you will remember from the lessons on malt, in cereals, starch exists as large and small granules (amyloplasts). There are amorphous (unstructured) and semicrystalline and crystalline areas of starch within these granules. In most cereals, the amylopectin:amylose ratio is around 75:25 in both granule sizes, but the starch in small granules needs to be heated to a higher temperature in order to gelatinise.