Editor’s note: This is the second in a three-part series in which ways to improve feed mill performance will be examined. The first article was published in the September issue of World Grain. The third and final article will be published in the December issue.

Some say the blending and mixing section is the heart of the feed mill, where the art of the nutritionist, miller and raw material buyer come together to make or break both the feed miller and the farmer.

As raw material prices rise and regulations tighten on what millers have available to feed livestock, the raw material buyer really does earn his keep, staying abreast of regulations and watching the markets in what have become quite volatile times.

With fuel sources becoming more expensive, agricultural inputs are continually rising. There are fewer opportunities to use byproducts from other industries than a decade ago, as rules and regulations preclude various ingredients from consideration. Pesticide residues, genetic modification, ethical concerns and finding crops with efficacies that are acceptable to the “green” movement all put constraints on the choice of ingredients.


Fortunately, there are sophisticated formulation software packages available today that can take in and generate more information than ever thought possible only a few years ago. While you cannot be expected to watch raw material markets constantly, there is monitoring technology that can tell you when you need to take action and either buy or sell the various commodities that make up the rations that are processed through feed mills.

Today, fully automated blending and mixing systems with downloaded formulations storage and parameters that are set externally for liquid addition, mixing times, routing to press and finished product bins, are the norm in almost every mill. However, there are several modifications available to most systems, many of which can show enhanced profitability for most mills. Blending accuracy, automatic adjustment of material in flight tolerances, and statistical analysis of actual ingredient inventory usage all help to maximize weighing accuracy and inventory controls.

Stochastics is a system of analyses that some mills have adopted in recent years, but it is mostly suited to mills that manufacture a limited range of feeds. It is ideally suited to mills making four or five poultry diets to supply a given outlet chain, where weight for age is crucial and can be varied according to how well finished chicken meat sales are progressing. Being able to dial in and adjust energy value in the blending system and come out with an instant change in the feed being placed before the birds later in the day is a luxury enjoyed by only a few, but one that pays handsome dividends where it is available.

Most millers use their formulation package to reformulate monthly, some weekly and a few daily. Formulae are usually downloaded directly to the mill batch control system either by direct link or by insertion of a CD into the mill PC. Whichever way data is transferred, the methodology allows for a quick change in recipes or formulations. By the same token, mixing parameters can also be changed quite quickly. Mixing times rarely vary and most millers adopt a three- or four-minute dwell time in a horizontal mixing system with bomb doors for effective cleanout.

Three-tier mixing systems are the norm, especially where more than one pelleting line is being fed. Some mills operate with multiple mixing lines, but these are invariably where multiple species are being fed through the one mill. These types of mills are becoming few and far between, principally because of the cross-contamination risks associated with multiple ingredients being processed through the same facility.

Most, if not all, mills have the facility for retaining detailed batch records, showing the desired ingredient inclusion and the actual weight of inclusion of each and every raw material into a

batch. Hand-tipped ingredients and micro additions are no exception, and in these days when traceability is all important, batch numbers, serial numbers and full details of ingredient origin can be retained for several years on either CDs or other simple storage devices.

Whatever your blending and mixing system comprises, there will be a need for effective and regular calibration of scales, pumps, meters and all other control devices, including electrical timers. Usually a simple manual schedule acts as a prompt for us to carry out such routine calibrations, but increasingly the use of automated calibration records are being generated. These are useful and can be done far more regularly than with manual calibration checks.

The generation of “as found” data is also becoming automated, precluding the possibility of erroneous mixes being dispatched without knowledge. Recall procedures are becoming more transparent as end users of processed meat become more sensitive to the public demand for perfect products.


With mixers also becoming more efficient in their design and mixing times being reduced, there is a trend toward premixing some ingredients, particularly trace minerals and vitamins and the smaller micro-ingredients that you do not want to process through the hammermills that are incorporated into post-grinding systems.

The use of premixers and screens before hammermills leads to a slightly more sophisticated blending system flow, but automated controls assist with simplifying the controls and increasing accuracy of mix and blend operations. With the trend toward split mixing, it does enable the miller to more accurately blend ingredients of much better aligned particle size spectrums. This subsequently assists with pellet mill performance and cooling as will be discussed in part three of this series.

Liquids addition is still done at the mixer in most mills, although the trend toward splitting the addition of fats and fat blends between the main mixer, where it is incorporated internally to the meal, and spraying a proportion externally to the pelleted feed continues to be the source of debate. Where pellets are coated with fats, the use of small batch mixers is becoming more prevalent. Swift but gentle mixers mounted on load cells in order to blend both fat addition and pellets by weight have largely replaced the volumetric systems you first saw when fat spraying became a feature of feed milling operations.

The use of stainless steel is the norm in mixers that are used where corrosive fats and other liquids are incorporated into rations, but mild steel mixers can still be seen in many mills. Stainless steel price differentials are not what they were a few years ago, and almost all the mixers are now made of stainless steel.

Bearings generally have caused little trouble, largely because of the slow speed at which mixers operate. Gearboxes have had their usual leakage problems, generally associated with the pressures they are put under when moving several tonnes of meal around in a closed environment. Bomb doors have sorted the problems of mixer hang-ups, and cleaning mixers out is almost a thing of the past. Some mills still have slide discharge either at one end of the mixer or at several points along their length, but they can lead to incomplete discharge of mixers, particularly when mixer blades become worn and a layer of material is allowed to build up in the base of the mixing chamber between the outlet slides.


Most mixers rely on compressed air for their operation, and good quality compressed air supply is essential to effective operation of bomb doors, inlet slides and diverter valves all associated with the modern day mixing and blending system. Regular maintenance of compressors, air lines, dryers and water traps is essential to a good control system.

Occasionally bomb doors cannot close properly because of low-pressure air that is not always detected by sensors. Accurate checking of output batch weights against desired input weights will often highlight problems with batch carryover, invariably traced to problems with compressed air supplies not being capable of keeping doors closed when the full weight of a mix is being processed.

As always, diligent examination throughout the mill is paramount, but nowhere more than at the blending and mixing stage of the milling process. Regular checking and perusal of mixing and blending records will show discrepancies and areas that can always be improved on. Making it the responsibility of one individual to glance through batch records will pay dividends over time once the individual becomes familiar with the manner in which records are kept.

Trend analyses are also useful and can be kept in graphical form, often as an automatically generated “add on” to the formulation package. Where the facility can use such analyses as a query tool within a software package, it can prove invaluable. With raw material values rising and showing no signs of abating, it is increasingly important to be more diligent about your mill operations. Incorrect blending and inaccurate mixing can be expensive, and you must be on top of the job at all times to survive these difficult times of world economics.

Jonathan Bradshaw is a consultant to the agribusiness and food processing industries, specializing in project management and bespoke training programs through his company, J B Bradshaw Ltd. He may be contacted at: [email protected]?.