Mill efficiency

by Emily Buckley
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Mills are high-volume processors of raw materials. This means that modest efficiency gains can yield significant volumes of final product or significant savings in running costs.

Key areas where efficiency can be measured and tackled:

• Raw material selection. Good quality grain will always produce good product and with less effort. Quality material will usually justify the premium it demands.

• Raw material preparation. Removing impurities from raw materials makes it easier to operate mills and produce a higher quality product. Moreover energy is not wasted in grinding screenings unnecessarily.

• Moisture management. Moisture addition is a key variable in getting the most out of mills. This area influences both product yield and mill operation. Don’t treat it lightly.

• The grinding and sieving process. There are upwards of 20 different grinding stages and as many more sieving stages in any mill. The mind spins at the number of permutations in settings that are possible. Getting it wrong can cost

phenomenal amounts of money and can justify the cost of employing good mill operatives and managers.

• Flour and wheatfeed collection and storage. This is where invisible losses creep in. Spillages, conveying losses, inaccurate weighing etc. all lead to efficiency losses.

• Packaging, warehousing and delivery. These areas are traditionally where highest losses occur and where they are most difficult to curtail. This is because of the nature of the operations performed and the fact that it is the interface with the outside world, where the mill operator has no influence over what happens to his product.


It is possible to influence overall performance in each of the above areas. However, the difference between the best operators and the average will be quite subtle. For example the best wheat buyers will know supply markets and suppliers intimately and always source the best grain, in terms of quality and purity. This can influence screening losses and extraction by one or two points.

Screenings adversely affect mill performance. The best milling operators achieve high milling efficiency by sending clean grain to the mill and grinding screenings directly into wheatfeed.

Traditionally, the grinding and sieving process is where most attention to efficiency management is centered. Experienced operatives can tell from a visual inspection how well a grind or sieving operation is being performed, but rarely will all operatives in a facility have this skill level. Thus, the best mill operators have in place systems that can be objectively employed to measure grinding and sieving performance. This does not necessarily mean a high-tech solution, but it does mean maintaining records and having routines.

There must also be a discipline regarding analysis of this information so that measurement results are consistent and complete. This is important because changes in performance may be linked to external factors (such as malfunctioning equipment) and if records are incomplete, the link between events may not be made.

An efficiency increase adding even only one or two percentage points in yield can result in a staggering amount of additional output annually. This results in obvious economic ramifications and the less obvious benefit of having a database built up

containing knowledge of mill performance and products. If the data gathered is used properly, subtle product properties can be manipulated to match customer requirements and therefore contracts can be won and secured. Moreover, the ultimate goal of flour milling can be more readily achieved — consistent products with consistent performance.


Bulk product conveying and storage is rarely analyzed from an efficiency perspective. However, conveying and storage conditions significantly influence so called ‘invisible losses’ in milling. Humidity control, filter losses, start up and shut down losses and even leaks and spillages are significant in the global sense and are worth scrutinizing. For example, spillages constitute lost product, are unsightly and cost money to clean up. They also are a major source of pest infestation in silo blocks and in mills. Eliminating leaks thus has major indirect cost and operational benefits.

Packaging, warehousing, and delivery systems are notorious for their losses. These losses are also notoriously difficult to tackle. Spillages, damages and returns all contribute negatively to the bottom line. It is an area that cannot really be tackled solely by the application of technology, but instead requires attention to detail. Subtle things like warehouse layout, pallet

presentation and even bag size all have an influence on losses and therefore plant efficiency. Operative feedback can yield some of the highest returns in efficiency gains, because it can often be random, unrelated events that create problem issues and everyday experience can point the way toward answers.



Mills should make use of its laboratory to measure efficiency improvement. Laboratories are equipped to measure and handle large amounts of data, and they are in a position to analyze and present this data in a meaningful form. The laboratory can

become an integral part of the process and contribute to mill profitability instead of being the ‘policeman’ in the plant.

Finally there are a number of other areas where mill efficiency can be addressed outside process operation parameters. For example, energy efficient machines generate small but definite gains, in terms of electrical requirement and heat generation. Machines with long service intervals save on downtime and servicing costs. Machines and buildings with good sanitary characteristics minimize losses and cleaning costs. Infestation is thus less of an issue and control measures are easier and cheaper to enact. The list goes on and on.

The operation of a mill is a complex process and attention to detail separates the best operators. This article serves to highlight the general areas where the drive for optimum efficiency can start. It is by no means an easy process and it must be worked on continuously. However, the operational and financial rewards are significant.