Lesson 4 - Milling Principles

We use a mill to gain access to the extract in the grain in the mash and to provide grist that will process easily during wort separation. The mill we choose, and how we operate it, determines how successful we are in these and subsequent steps in the brewing process.

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In mashing, we need to produce the maximum amount of extract and the correct sugar spectrum for the beer we are producing. The finer the malt is comminuted, the more extract we will produce. This is because more of the endosperm is exposed and so it can be converted by the enzymes in the mash. Failing to comminute the malt sufficiently will lead to slow and incomplete conversion, so extract efficiency will be low. Fermentability may also be lower as saccharification will not proceed as far in the same time frame.

During wort separation in a lauter tun or mash tun, we rely on the husk fragments to act as a filter bed. If our comminution is too fine, the porosity of the filter bed will be reduced and wort separation will be slow and more difficult. Finer comminution also leads to extraction of more β-glucans and other non-starch polysaccharides. These increase wort viscosity and can also reduce filter bed permeability, both of which slow wort separation. Slow and troublesome wort separation often leads to hazy wort and lipid extraction, which both negatively affect foam and flavour stability. Finer comminution also means that more husk is exposed to mashing and sparging water, so more polyphenols may be extracted. Polyphenols can cause hazes in the finished beer and some believe they make beer taste astringent. When using a mash filter, the size of the husk particles is of less importance, therefore fine comminution is preferred.