Lesson 8 - Milling Lesson Final SAQ

***You are a technical sales representative for a mill manufacturer who supplies a range of six-roller and hammer mills. Prepare a technical summary of the benefits of each type and a recommendation of the best option for an undecided customer.

Response:

The most significant consideration in the customer’s decision is the wort separation device that they currently use or are planning to use. The ultimate recommendation we give them will be driven by this. The six-roller mill is capable of producing a grist that will be processed easily with a mash filter, but the extract efficiency will always be poorer than with a hammer mill. If they are going to use a six-roller mill with a mash filter, we would recommend having all the rollers fluted and that all roller sets are arranged to have cutting edges against cutting edges. If they have, or have decided on, a mash filter − our recommendation would be a hammer mill. As well as giving superior extract efficiency, maintenance costs are lower − and being a simpler machine, the purchase costs are typically lower. Hammer mills are also able to mill any type of grain apart from highly friable speciality malts, so they give more flexibility for variation in malt modification and the type of adjuncts to be processed.

If space is at a premium, a vertical hammer mill would be the best option as its footprint is lower. If the brewery has the requirement to prevent grist oxidation, a system that flushes the mill and grist case with either CO₂ or nitrogen would be advantageous. The energy costs for a hammer mill are higher than that of a six-roller mill at 4.4 kWhr/t of malt, but the increase in extract efficiency more than makes up for this extra cost. This may not be the case if energy costs rise, but grain prices are typically tied to energy costs, so this is unlikely.

If the customer is going to use a lauter tun, there is only one option. The grist from a hammer mill would be too fine and uniform for a lauter tun. The grist has a high proportion of fine flour, flour, and fine grits. Furthermore, the size of the husk fragments required to establish the lauter filter bed is too small to provide the required permeability. Lautering would be at best slow and problematic. Of all the dry mill options, the six-roller mill gives the most suitable grist particle size distribution for a lauter tun, producing a high proportion of husk and fine grits. It provides a far better extract efficiency than the two- and four-roller mills and is able to mill malts of lower modification levels more effectively. If the customer is going to operate very large lauter tuns, the six-roller mill will be able to achieve the required throughput whereas wet mills will not. It also requires less cleaning, uses less water, and produces less effluent than wet mill options. The bed loading and rate of wort separation will be lower than wet mills, but a conditioning screw could be used to reduce the shortfall. This would also reduce mashing times and improve extract efficiency. If the brewery has the requirement to prevent grist oxidation, a system that flushes the mill and grist case with either CO₂ or nitrogen could also be employed.

If the customer has or is considering using a mash tun, the six-roller mill is the only option that might work − but it would need to be used with much wider mill gaps. If this is discussed, we would probably politely suggest that a mash tun is not the best option for modern mashing and wort separation!