Lesson 6 - Milling Technology

Although not always situated in the brewhouse, the mill is integral to brewhouse operations. Without the right mill, even the best brewhouse will not perform effectively. Compatibility with the mashing and wort separation systems is therefore the first criterion on our mill selection checklist. Let’s discover the other criteria that we need to consider.

The factors that we need to consider when selecting a mill are as follows:

• Purchase price (including grist case, pre-masher, installation, CIP connections, safety equipment)

• Operating costs (energy, water, effluent, and maintenance)

• Available malt quality (level of modification and variability)

• Requirement to mill adjuncts

• Grist requirement of mashing and wort separation systems

• Ease of integration with brewhouse automation

• Extract efficiency

• Capacity

• Space required for mill and ancillary equipment

The decision regarding which mill to buy can range from very simple to quite complex. Almost all steep conditioned mills are supplied by brewhouse suppliers as part of their standard brewhouse packages, so if you buy their brewhouse, you will buy that mill.

For use with a mash filter, the choice is between a hammer mill or an underwater disc mill or DISPAX®. The underwater disc mill or the DISPAX® mill give the best protection from grist oxidation, followed by the Carbomill. If oxidation is not a concern, the lowest capital cost option is a standard hammer mill. Although six-roller mills have been used with mash filters, they are an expensive option and do not give as fine or uniform a grist as the other technologies we have just described.

For a lauter tun, the best lautering (wort run-off) performance is provided by the grist from the full steep wet mill, however, these mills are no longer manufactured. The next best option is the steep conditioned mill, followed by the conditioned dry mill. Most lauter tuns operate with six-roller dry mills because these have low operating and purchase costs, the fewest problems, and provide acceptable performance.

The coarse grist required for a mash tun can only be produced effectively with a two- or four-roller dry mill. The two-roller version is the lowest cost option but the extract produced from a four-roller mill is superior, especially if the malt modification varies.

The scale of the brewery is also a factor. Some of the mills are only available up to or below specific sizes, so may not be suitable for very large or very small breweries. The minimum cost and space requirements of some of the mills are also so high that they are not sensible options for breweries below certain sizes. For breweries below an annual output of around 5000 hL per year, the only sensible option is a simple two-roller dry mill.

The table below summarises what we have just learned about the mill types and draws a comparison between them for important selection criteria.

Table: Mill comparisons

The choice of mill must be made with a good understanding of operational and commercial factors. Once we have identified the best mill for our wort separation system, the decision is likely to be a balance between the upfront costs and long-term benefits from high extract, reliability, and low operational costs. And of course, all decisions in brewing need to consider the quality of the beer produced.