Lesson 7 - Milling Technology SAQ

*Rank the following mills in order of their effectiveness at producing a desirable grist and attaining optimum extract efficiency from under-modified malt. Explain your reasoning.

•  Six-roller conditioned dry mill

•  Steep conditioned mill

•  Hammer mill

Response:

The correct ranking is:

1. Hammer mill

2. Six roller with conditioning

3. Steep conditioned mill

A significant proportion of the endosperm of under-modified malt is poorly friable. This means that the force required to break down the structure is greater. As the mill that applies the most force to grain, the hammer mill is best suited to effectively comminuting poorly or under-modified malt to expose the starch for conversion during mashing. Of course, the grist will only be desirable if the brewhouse has a mash filter. The particle size profile of the grist would cause major problems if used in a lauter or mash tun.  

Six-roller conditioned dry mills have three pairs of rollers, so fragments of unmodified malt can be compressed and sheared three times as they flow through the machine. The screens in the mill will separate them from the rest of the grist, ensuring that the valuable husk particles are not comminuted excessively and the overall particle size distribution is not skewed towards finer particles. The grist produced would be suitable for a lauter tun. It would be too fine for a mash tun, resulting in a sunken mash bed and very slow wort separation. Although the six-roller mill grist would process easily in a mash filter, the extract efficiency would be inferior to that which could be achieved from a hammer mill grist.

The poorest performer of our three mills is the steep conditioned mill. With one or sometimes two pairs of rollers, steep conditioned mills cannot apply sufficient force to break down the poorly friable unmodified endosperm fragments. The control system can slow the rate at which the grain is processed, which provides greater hydration and more intensive milling − but this cannot compensate for the lack of force. Poorly modified portions of malt kernels do not hydrate easily, so the extra hydration will have a very limited effect and even at the slowest throughput, the endosperm does not hydrate by more than a few percent. Because hydration of the grist is largely complete after the mill, the grist produced is not suitable for a mash tun, and like the six-roller mill grist, it would give comparatively poor extract efficiency in a mash filter.