Lesson 5 - Milling Principles SAQ
This lesson allows you to test yourself on the material covered in the Milling Principles lesson, and determine the level to which you have met the learning outcomes.
SAQ Suggested Response - Q2
***You have been asked to improve extract efficiency by optimising the mill settings on your brewery’s four-roller mill. What would you do, what do you need to avoid, and what would you check before and after adjustment?
Response:
Extract efficiency is the amount of extract in the wort as a percentage of the amount of extract in the grain. The more finely the grain is milled, the more extract we are able to remove from it. A narrower mill gap produces finer grist. It is therefore sensible to see if there is scope reducing the mill gap. Before this is done, it would be worth checking to see if wort separation is going to plan. If the brewery is struggling to achieve the target time for run-off, or if the wort clarity is not always satisfactory, any tightening of the mill gaps would lead to big problems. We must undertake plansifter analysis of the current grist so that we have a starting point for any changes. This should be checked against the brewery’s specification to see if it is out of specification. If it is already at the bottom of specification, it is probably unwise to make it any finer. If everything is running well in wort separation and there is some room to reduce particle size on the specification, we can look to narrow the mill gap. We also need to ensure that we have extract efficiency figures for the current malt batch and current mill settings. We would then adjust the mill by a few percent to reduce the gap size.
After adjusting the gap, it is wise to check the new gap with a feeler gauge to ensure that it has changed to the required extent. We should also run some card through the rollers to ensure they are still completely parallel. The grist produced by the new settings should be checked as soon as milling commences, using a plansifter to see what profile has been achieved and that this is still in specification. If everything is fine, the next task is to monitor wort separation and to calculate the new extract efficiency. If wort separation is still proceeding well and extract efficiency has improved, we can report to the brewing office for a ‘pat on the back’! If the improvement is significant, the recipe will need to be adjusted to use less malt. We should continue to monitor milling and wort separation performance to ensure it is problem free and within specification. We should also check to see if further improvements in extract efficiency through mill gap adjustment are possible.