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Digital Re-print - January | February 2010 Feature title: Wheat Preparation - Cleaning, Conditioning & colour sorting

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A few years ago these three topics would not have been considered in the same

article. However today, things are quite different and colour sorters are now considered an integral, if not always significant part of any modern day wheat cleaning flow and now there are few screen rooms that do not have at least one colour-sorting device in the flow, of one sort or another.

Not always part of the main stream, but certainly a significant weapon in the miller’s armoury these days!

And when we consider cleaning and preparing wheat for milling, perhaps the most important aspect of having wheat in a suitable state for arrival at first break is the way in which we carry out the conditioning process. There are more problems that arise on the mill due to poor and inaccurate tem-pering or conditioning than any other single process before first break.

Dry wheat, wet wheat, wheat with variable moisture spread unevenly through the kernel, all of these items can give the miller quite a headache and all are so easy to identify, resolve and correct.

Five principles of separation

We were all taught the five principles of sepa-ration when we studied for our milling exams and the same principles

still apply – obviously, since wheat has remained unchanged, physically, despite the best efforts of the plant breeders.

However, we no longer use separate items of equipment to remove each type of impurity in every screen room since, thankfully, and because of better harvesting techniques, I dare to proffer that wheat is much cleaner than it used to be when it arrives at the mill.

Now that wheat is traded at 15 percent moisture content as opposed to the 16 percent which was the case up until the late 1980s, it is inherently cleaner just because impurities naturally separate away much easier at lower moisture levels. With many farmers also using central, common grain stor-age facilities post harvest, where grain is cleaned to within the accepted two percent limit for impurities prior to storage, the role of the cleaning house, certainly in new mill installations, is very much reduced and screen room flows are consequently greatly reduced in terms of machinery content.

We now use drum separators on intake in much the same way as we did in the mid-20th century, principally, just as a policeman to control large impuri-ties, wood, tramp metal and masonry, often dug up by loading shovels when scraping the last of a season’s grain out.

by Jonathan bradshaw

“Dry wheat, wet wheat, wheat with variable moisture spread unevenly through the kernel, all of these items can give the miller quite a headache and all are so easy to identify, resolve and correct”

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The sturdy, robust and reliable drum separator

Most drum separators are much more sturdy than those produced even a few years ago, we don’t see the heap of twisted metal screen in the corner of the silo any more, principally brought about by a large lump of tramp metal being allowed to pass through the intake pit grid, left ‘ajar’ by the driver keen to get on his way.

Drum separators, particularly the Buhler and Satake machines, are now extremely robust and reliable, the former having lived through and developed in some really harsh conditions in North Africa and the Middle East and the latter having being developed in the maize mills of East, Central and Southern Africa where they have had to be robust to survive.

Grain storage timesHaving given grain a tertiary clean at the

first point of intake we then store it in dirty wheat silos until it is needed. Grain storage times are much shorter these days since finance does not allow us the luxury of stor-ing grain in quantity, and there is little point in just having grain sat there in storage when money can be better used elsewhere.

However, in some circumstances we can-not avoid having to store some grain.

Imported, specialty wheat, for exam-ple, that may well have been shipped as

a part cargo, split down and shared by a group of indi-vidual millers from an ocean going Panamax or similar sized vessel on coastal vessels from Europe and on which the minimum freight quantity may be greater than we would normally deem acceptable in financial terms for everyday storage.

In such cir-cumstances, in order to main-tain the quality and freshness of this stored grain it is my belief that it should be reg-ularly turned over from one bin or silo to another and

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around two mm diameter and invariably slotted to avoid blinding too often, although it is becoming more regular to see coarser bottom screens, up to five mm slots and then subsequent independent treatment of the grain stream to recover sound wheat rather than the continued removal of impuri-ties.

The reasons behind this are that it allows the separator to operate for long periods of time without blinding up and it ensures that screenings are kept to a minimum.

Gone are the days when we sought to remove every last impurity, rather that we keep a part grain in the stream through first break and support the economic equation of maximising yield which is what we continu-ally strive for in all mills.

It is quite a while since we spent hours as millers seeking that last 0.1 percent extrac-tion from the mill itself having just thrown away 0.2 percent in the screen room in order to let us achieve this. Thankfully such false economies have now been realized and corrected.

Back to colour sorting & mycotoxins

Moving on, we see a plethora of bespoke machines, usually involving some means of stone removal, some gravity separations and occasionally some other specialty process depending on the local growing conditions in the area around the mill or perhaps because of some national or international change in wheat quality as we currently see with unac-ceptable mycotoxin levels being the reason for some millers increasing the scouring capabilities within the wheat cleaning plant or perhaps adopted peeling or debran-ning techniques as part of their processing philosophy.

I don’t propose to dwell on this subject here as it is addressed elsewhere quite adequately.

As far as colour sorting is concerned and in connection with mycotoxins, there are those who believe that mycotoxins can be treated to highlight the level of contamina-tion by a variance in colour, usually red and then use this colour variation to separate out the offending grain kernels.

Some others believe that density or hag-berg levels will vary according to the level of mycotoxin present.

Personally, whilst I applaud the research work being done, I have yet to be convinced that there is any form of practical applica-tion of this technology yet in operation in any mills, wherever they may be, and await developments before signing up to any ‘wonder cure’ for the unwelcome mycotoxin levels we currently see.

Perhaps more useful and practically appli-cable is a good housekeeping regime, regular

we have come to expect from the ever-dependable Swiss.

Following on from the blending station, the first machine we see in all screen rooms is the milling separator, adequately protected by magnets at the inlets and usually equipped with an aspirating leg at the outlet.

Occasionally we see aspiration at the inlet, particularly in organic mills where long straw is a particular problem. Organic grain, when growing naturally, tends to have longer straw than wheat grown under more chemi-cally controlled conditions, but, since organic grain is sold at a premium, the farmer or con-tractor has no desire to allow any to fall to the floor in the field as it is harvested, hence it tends to be treated with ‘kid gloves’ and as well as maximising the amount harvested, along with the grain itself comes a wider range of straw and impurities than we tra-ditionally associate with conventional grain.

Coarse rubble screensAll separators are equipped with coarse

rubble screens generally around 10mm in diameter and finer, sand and seed screens

aerated in order to keep it in its best condition.

Most grain, coming from central storage or from farm directly to the mill is only in our silos for a few days, or weeks at maximum, and sometimes only hours.

Wheat of different varieties and different analytical qualities are blended from the dirty wheat bins and this procedure is becoming more important as quality wheats demand premium prices in the market place. This need to blend more accurately is not just because of finances, but also from a regular quality control point of view.

Loss-in-weight becoming more widespread

The use of loss-in-weight feeder is becoming more widespread and the demise of the volumetric feeder is now almost complete. The Buhler flo-balancer is still very popular at home and abroad and can always be relied on to provide accurate blends. This workhorse for many years is being replaced with even more sophisticated and reliable machinery, as

The Satake, AlphaScan II 160 High Flow grain color sorterImag

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colour sorters at both customers and suppliers plants can alleviate any disagree-ment between the two parties.

For this reason it is often quite com-mon to see the retreat channel on a col-our sorter, used as a ‘policeman’ for the whole plant to ensure cleanliness of the grain stream rather than just cleanliness of the grain passing through the colour sorter.

I have no doubt that the application of colour sorters will continue and the scope of use will continue to widen as ideas develop and theories are proven. More on this subject in future issues.

Basic principles of conditioning

And to conclude this article we are led to the contentious subject of conditioning grain. How long should we condition or temper for? Should we temper in one pass or two, or, in some cases, three, where wheat is very dry? The debate has been going on for generations and I doubt whether I will answer all the queries at one shot, however, it is my belief that there are some basic principles to be adopted and if these are adhered to the results will be adequate for the costs incurred.

These basic principles are firstly to match the number of passes to the level of mois-ture being added, obviously having due regard to ambient temperature.

I hesitate to give a percentage rate, since

colour sorters is that they take up very lit-tle space, require little or no steelwork to support themselves and can be brought on line at the flick of a switch – almost ‘plug & play’ as modern jargon would refer to it.

Another significant role for the colour sorter in specialty situations, where per-haps breakfast cereals are the end result of their use is that it is quite easy to standardise the calibration of a machine.

There has often been dispute about the ‘true’ level of impurities in any deliv-ery of grain used for further processing by breakfast cereal manufacturers and a simple reference sample run through

cleaning of silos and a sensible decision as to when is the right time to harvest, dry and store grain. No doubt many will challenge my views in days, weeks and years to come. Your comments are welcome, as always.

Colour sorters can be used to good value in several areas within the wheat cleaning plant, the most common areas thus far in the older mills, and by that I refer to mills built circa 1980 and earlier, and are used in order to tidy up the general layout of a plant and remove old banks of disc separators and trieur cylin-ders that are either badly worn out or no longer performing satisfactorily.

Some of the obvious advantages of

“The small things that the trained eye can see will make a world of difference whether they are left untreated to create havoc at a later date or whether they are dealt with immediately by the diligent manager who then goes on his way knowing that he is on top of his job and can turn his attention to the more significant aspects of management”

“Good management of silos is also crucial to effective

tempering and regular inspection and cleaning of silos

is vital to a mill’s operation”

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easily at all time by silos operators or con-tract cleaners alike.

Daily walk-aroundRegular schedules for filter cleaning will

help keep dust levels to a minimum when working in a silo and it is not beyond com-prehension to coincide filter maintenance with silo maintenance so that filters can be cleaned and serviced immediately prior to full inspection and cleaning of individual silos.

And throughout all the items I have referred to in this article there is a need for good management to control all operations.

That daily walk round, using a checklist (mentally stored or printed out and used as a record) is of vital importance.

The small things that the trained eye can see will make a world of difference whether they are left untreated to create havoc at a later date or whether they are dealt with immediately by the diligent manager who then goes on his way knowing that he is on top of his job and can turn his attention to the more significant aspects of management … or at least those items who appear higher on his or her superior’s agenda!

flour mill site, or indeed any other type of mill including rye, maize etc.

Silo management and effective tempering

Good management of silos is also crucial to effective tempering and regular inspection and cleaning of silos is vital to a mill’s opera-tion. Each miller will have his own view as to whether he should use his own staff and equipment to inspect and clean silos.

Some millers choose to use an outside contractor for all confined space entry work, if for no other reason than to absolve them-selves and their employees of the liability that such work involves.

Others choose to manage the risk and train staff accordingly and minimise the expense that contractors will charge. Either way there are some items in the early stages of mill design that can make life easier for whoever is carrying out the cleaning and inspection.

Good access and ventilation provided by sensibly sized access doorways or silo ingress facilities at the top will assist greatly. Good internal lighting is of great value, as is a fixed supply of clean air, which can be accessed

nearly every miller will have a view that conflicts with mine and which I am sure is derived from many years’ practical experi-ence, suffice to say that I believe in generous allocation of tempering capacity at first tem-pering and I also believe in using that space to its maximum potential at all times.

It is acceptable, to leave some space unused after a mill is built if that space is not required for the wheat moisture pertinent at the time, but you cannot add space effec-tively if requirements are underestimated at the design stage.

First-in first-outAn important criteria is the use of First In

First Out (FIFO) techniques when designing bin outlets. All millers are familiar with the, multiple outlets, evenly spaced, etc.

This allows grain to do exactly what the principle describes, let the first grain that was damped to be the first grain to pass out to either first break or the next phase of conditioning. Without this type of bin outlet the operations of effective tempering will be severely compromised.

In fact, I belief this methodology should be applied to all grain bins and silos on a

Grain&feed millinG technoloGy January - february 2010 | 23

Feature Wheat

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Preparation Cleaning, conditioning

& colour sorting

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