Lesson 8 - Milling Lesson Final SAQ

**How can malt intake and storage set milling up for success and how can it set up milling for failure?

Response:

A good way to answer this question is to address how intake and storage affect the objectives of milling. We can start by listing the objectives:

• Produce the required particle size distribution for the mashing and wort separation systems used

• Maintain the required level of husk integrity for the wort separation system

• Maximise extract efficiency during wort production

• Operate safely

• Achieve the programmed brewhouse cycle time

We will now explain how malt intake affects each objective.

Produce the required particle size distribution for the mashing and wort separation systems used

For mills to achieve this objective, malt needs to be delivered to the mill without damage to the kernel and at the specified moisture level. Effective intake checks will confirm that the grain meets the brewery’s specification. Corns that are smaller than specified will not be milled effectively by roller mills, so evaluation of corn size is necessary. The degree of modification and friability will also help ensure that the grain has the friability required to be processed effectively by the mill.

If storage is not undertaken correctly, pests can damage grain and it may also pick up moisture or dry out. If the moisture is too low, the grain will fracture too easily during milling and a smaller particle size will result. Excessive moisture may also affect comminution by making the grain less easy to fracture and by increasing particle sizes.

The malt needs to be handled gently enough to prevent the grains from becoming damaged. If damaged malt is delivered to the mill, the particle size distribution will be less easy to control and is likely to be smaller than desired.

With roller mills, damage to the roller will cause a change in the particle size distribution of the grist produced. The processes that remove foreign material such as screens, magnets, and destoners all help to prevent damage to the rollers.

Maintain the required level of husk integrity for the wort separation system

As with the last objective, for the level of the husk integrity to be maintained, the malt delivered to the mill must be undamaged and at the correct moisture level. If the moisture is too low, the husk will fracture easily and if the grain is damaged before the mill, husk fragments are likely to be smaller than required. Intake checks and control of the conditions during storage should ensure that the moisture level is as required. Gentle handling will also ensure that the grain arrives at the mill intact so that the fragmentation of the husk can be controlled by the mill.

Maximise extract efficiency during wort production

This objective is another where intake checks are instrumental. Making a laboratory mash based on the EBC or IoB method will confirm that the lab extract potential for the malt is within specification.

Maintaining the correct moisture level is also very important. If the grain picks up moisture in storage, it will contain less extract as a proportion of the grain milled. A 1% increase in moisture adds 100 kg of water to a 10 t grist! Higher moisture levels also increase the likelihood that the enzymes in the grain will deteriorate and pests will damage the grain. Both will result in reduced extract efficiency. One from loss of extract to pests, and the other from a lack of enzyme activity to undertake starch conversion.

Ensuring that malt stocks are sufficient for the immediate brewing plan and that they do not require extended storage will minimise the risk of pest damage and moisture uptake.

Another source of extract loss in grain handling is damaged grains. Damaged grains are likely to get screened out. Damage also results in dust that will be removed by aspiration and disposed of. In addition, damaged grains are more susceptible to taking up moisture and becoming damaged by pests. Gentle handling ensures that these extract losses are kept to a minimum.

Operate safely

There are two aspects of safety that can relate to milling. One is the safety of the staff in the brewery and the other is the consumers of the beer. Intake checks will help confirm that the malt is free of moulds that may produce mycotoxins and also any contamination with fuels or solvents. Correct storage conditions and safe management of pesticide application will also help ensure that staff and consumers remain safe.

The main safety hazard associated with malt is dust. Dust aspiration systems help to ensure that levels are kept low and that dust does not leak into the work place. This reduces the risk of explosions and dust inhalation. Properly designed grain handling systems reduce damage to the grain and hence dust generation. They also include safety systems that prevent or limit explosions. The risk of explosions during milling is reduced by the malt intake equipment that removes foreign materials (which can cause sparks). Destoners, screens, and magnets should remove most of these, but a thorough visual inspection of samples on intake should also help.

Achieve programmed brewhouse cycle time

To achieve the brewhouse cycle time, milling must not delay mashing in. If the mill is a wet mill, milling is part of the mashing in process, so a breakdown will delay the brew and in some cases may even lead to the brew being destroyed. With dry milling, the window for milling is larger as it equals the residence time of the mashing vessel. Malt intake and storage can help prevent breakdown by removing any foreign material likely to cause damage to the mill. It also prevents breakdowns by ensuring that the mill is fed at a rate that will not cause blockages and with malt at the correct moisture level.