Lesson 7 - Milling Technology SAQ

**Explain how a steep condition mill overcomes or mitigates the problems associated with a full steep wet mill.

Response:

The problems associated with a full steep wet mill are:

• Difficult to keep clean

• Requires frequent CIP

• Has the highest water use and effluent generation of all mill types

• Plansifter for grist analysis cannot be used

• Operating conditions can cause corrosion

• Increased risk of malt and mash souring with plant stoppages

• Cannot mill some adjuncts and under modified malts

• Difficult to operate consistently

We will now take each in turn and see if, or how, the steep conditioned mill overcomes and mitigates them.

Difficult to keep clean

The difficulties in maintaining good hygiene are probably the main reason why full steep wet mills are no longer manufactured. The steep conditioned mill, although less prone to hygiene problems, is still not as easy to keep clean as a dry mill. The main improvement in cleanability in the steep conditioned mill is that only the steeping chamber and the mill itself contain damp grain and mash. This means that there is less to clean. The residence time where wetted material sits in the system is also a lot lower, leading to a slower build-up of soil on the surfaces. As material flows through the steeping chamber and mill, there is a degree of self-cleaning that you don’t get in the steeping hopper of a full steep wet mill.

Requires frequent CIP

This point links in with our last, in that because there is less to clean, and the residence time is shorter, the steep conditioned mill requires less frequent CIP than the full steep wet mill. The design of the mill is also such that it is easier to clean effectively, which also reduces the required frequency. CIPs and inspections are still more frequent in a steep conditioned mill than in dry mills.

Highest water use and effluent generation of all mill types

With steep conditioned mills, any excess steeping water is typically used as mashing water, and there is no washing of the grain. This means that brewing water use is less than in a full steep wet mill. The requirement to CIP it less frequently, and the fact that there is less to clean, also means that the steep conditioned mill has reduced water use and effluent generation.

Plansifter for grist analysis cannot be used

It is not possible to use a plansifter analysis for steep conditioned mills, so this disadvantage is not removed. Grist analysis is less important for wet mills because the most important aspect of the analysis is to ensure that there is the right level of unbroken husk material for the wort separation device. With wet mills, this is pretty much guaranteed. That said plansifter analysis does provide an element of quantitative measurement that is missing when visually examining the grist/mash.

Operating conditions can cause corrosion

This is another area in which the steep conditioned mill does not provide a significant improvement. There is less material in contact with corrosive liquids, but the threat is still there. Use of the appropriate materials of construction, such as high quality chrome steel for the rollers, minimises the effects of the conditions. 

Increased risk of malt and mash souring with plant stoppages

As grain is only wetted when mashing in commences, there is less risk of the malt souring if there is a delay, breakdown, or stoppage with the steep conditioned mill. This reduces but doesn’t completely remove the risk.

Cannot mill some adjuncts and under-modified malts

With the ability to control steeping time and milling speeds, the steep conditioned mill can mill under-modified malt more effectively than the full steep wet mill. As they are designed principally to maximise the size of husk particles, it is unlikely that wet mills will be selected for adjuncts such as grits that don’t have husks. Also, grits are not pregelatinised so they need to be fed to a cereal cooker rather than a mash conversion vessel − and these mills are only designed to fill one vessel. The inability to mill these is not a concern unless you are limited to only one mill in the brewhouse. 

Difficult to operate consistently

It is difficult to operate full steep wet mills consistently due to the time of steeping and the changes to the malt that result. The volume of water to be added and removed from the steep is also hard to reliably control. The process used in the steep conditioned mill is much more consistent and easier to automate. The capability of mill automation has also greatly improved since the days of the full steep wet mill. Modern steep conditioned mills operate effectively and without the need for continual manual intervention in today’s fully automated brewhouse.