Lesson 8 - Milling Lesson Final SAQ

***What do we need to achieve in malt conditioning, milling, and mashing in? How do we ensure process consistency?

Response:

What do we need to achieve in conditioning?

Conditioning means increasing the level of husk moisture to make it more pliable and hence less likely to fracture when milled. We need to ensure that the husk is hydrated evenly and to the required extent. We are not trying to increase the level of moisture in the endosperm, but conditioning the full steep wet mill can increase its moisture level significantly. We need to ensure that hydration of the husk occurs within a set timeframe so that subsequent processes are not delayed. We also need to ensure that the enzyme potential of the malt is not significantly reduced by the temperatures used. Where LOX is a concern, in steep conditioned milling we can also use water at a higher temperature (80°C) to help denature this. Water at this temperature in full steep wet milling is would destroy too many of the malt enzymes. The residence time and water/steam applied in conditioned dry milling are not sufficient to achieve a significant effect.

What do we need to achieve in milling?

Milling is the comminution of the grain in order to allow the extraction of desirable substances in mashing. We also need to mill the grain to produce a particle size distribution and degree of husk integrity suitable for the wort separation equipment we are using. Milling must be fine enough to enable the enzymes in the mash to access their substrates, but not so fine that we extract undesirable material or encounter problems in wort separation. Where flavour stability is a concern, we need to minimise the exposure of the grist to oxygen and heat. Where the malt is conditioned, we need to ensure that the mill can keep pace with the required residence time of the conditioning process so that delays do not lead to exposure to excess moisture and heat. Milling needs to cope with the degree of malt modification required in the brewery’s specification. For wet mills, the mill also needs to process malt rapidly enough to meet the required mashing in time. Milling must not compromise the safety of staff or consumers of the finished product.

What do we need to achieve in mashing in?

Mashing in is the filling of the mashing vessel with hydrated grist. We need to ensure that the correct water to grist ratio and the required level of grist hydration is achieved. This will be different depending on the wort separation device used. As well as the correct water to grist ratio, mashing in also sets the starting temperature, so we need to ensure that the required value is achieved. Mashing in needs to be undertaken in the minimum timeframe as the mash conversion vessel and equipment is tied up while it is in progress. As with milling, if flavour stability is a concern, the availability of oxygen needs to be kept to a minimum. We also need to ensure that the movement of grist and mash does not change the particle size distribution we have achieved in milling.

How do we achieve process consistency?

To control the consistency of any process, we need to measure and control the inputs, (raw materials) process parameters, and process outputs. We need to specify target values for each and if they are not consistently achieved, take corrective action.

A suitable malt specification needs to be agreed with and met by the malt supplier and intake checks must be undertaken to ensure it is being met. The malt specification should be such that any natural variation of the malt does not necessitate continual adjustment of the milling and mashing parameters.

Water used for conditioning and mashing in needs to be analysed against a brewing water specification. The temperature and flow rate of water needs to be specified and continuously measured against the required value and controlled. The flow rate of the malt and grist also needs to be measured regularly and adjusted if not at the required value. All measuring devices need to be calibrated and this calibration should be checked as frequently as practicable. These include flow meters, thermometers, inline weighing scales, and laboratory equipment.

All equipment must be regularly maintained and inspected according to a set schedule. Condition monitoring on elements such as bearings and motors can also be used.

Grist analysis using a plansifter must be undertaken on every batch milled at set intervals and the results must be compared to target values. A visual evaluation should be used on wet milled grist. Where oxygen control is required, dissolved oxygen levels in water and mash should be measured along with the volumes of purge gasses used.

Extract efficiency and wort separation parameters such as differential pressure, flow rate, and time must be measured downstream and the information should be fed back to the milling and mashing operation.