Divides In a Flour Mill

by Teresa Acklin
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How their production can enhance profits

By David Sugden

   What is a divide? A stream of flour that has been detached or removed from other flours being produced simultaneously. Why make divides in a flour mill? Customer demand and money; a divide is sold separately for different purposes from other flours.

   The diagram at left illustrates a divide flow in a flour mill, and the accompanying table shows the origin of the flours. The table depicts not only the proportion of total flour for each of three collecting conveyors that immediately follow the mill, but also demonstrates the typical ash or mineral content of each. The flour collecting conveyor numbers in the table correspond to those at the top of the diagram.

   The diagram flow starts at the top with the three flour collecting screw conveyors. The conveyors contain flours of increasing ash content — measured in this example on a dry basis — with conveyor 1 having the lowest ash and conveyor 3 the highest. The conveyors collect flours from the mill as they are produced.

   Flour from each line continues through sifter redressers, magnets and metal detectors. At this point, each flow enters the so-called "divide board," motorized in this example for automation.

   The divide board has two valves that are completely movable from one side to the other. Flour divides are made by varying these valves.

   A typical divide board fed by gravity, not air conveyors, measures approximately 90 centimeters high, 60 cm wide and up to 30 cm deep. As seen in the diagram, the flow can be infinitely variable because 100% of any of the three flours can be diverted to each of the following three outlets.

   Flour passes from the divide board through separate on-line near infrared measuring instruments to check ash, moisture and protein content continuously. The function of the NIR sensors is to monitor the flour and control the motorized valves at the divide board to assure, by a feedback loop, that flours are within preset specifications. Flours then pass through infestation destroyers and finally to separate bins, labeled according to flour type.

   The diagram reflects one of a myriad of variations in use. Although this example is geared for automation, manual systems are common; indeed, only a few divide systems in the world are as sophisticated as this example.

   As shown in the table, flour collecting conveyor 1 contains the top reduction flours. These are commonly the top four to six reductions, which in North American terminology encompass sizings and up to four middlings. In the United Kingdom, they are known as A to D or E reductions, while other countries use different names. Nevertheless, they all are top reductions with the lowest ash content as the flours come from the center of the wheat kernel.

   Flour collecting conveyor 2 typically contains the top break flours, e.g. breaks I, II and III, plus the middle reduction flours. Conveyor 3 collects the remainder.

   The proportions from each conveyor as well as the ash content will vary according to the wheat quality milled. It is also worth noting that there is nothing rigid about these origins; many mills worldwide have facilities that can place flours normally destined for one conveyor to another conveyor upstream from the divide board, or even as a separate "bleed off." A number of important points should be considered about manufacturing divides. Some mills have flour blending systems within their bulk storage facilities to blend flours and allow additive treatment (additive treatment is not shown in this diagram, but it commonly is included in such systems). But divides cannot be made with flour blending equipment; the only point at which divides can be made is immediately following the mill.

   It is especially necessary for the practicing miller to have the laboratory check the divide flours as regularly as it does the more standard straight grade. Divide flours have a nasty habit of reflecting wheat and milling quality variation even more than straight grade.

   Further, the miller should have a table of the laboratory measured characteristics of each individual flour at hand; most mills have upwards of 20 individual flours. This is a major job that should be carried out perhaps every six months.

   Laboratory figures then can be matched to the stock quantities (weight over unit time) of each machine or individual flour. By simple mathematical calculation, it is possible to estimate the probable extraction for any given ash content on a cumulative basis.

   The same technique is used for protein. Testing for other parameters is possible but is less accurate because of greater experimental error.

   It is the marketplace, of course, that dictates the demand for divide flours. While the norm is for straight grade, certain clients will request patent or low grade.

   Patent flours of low ash content are usually sold at a premium to straight grade. Low grade at high ash content is commonly sold at a discount. This is in part due to the greater sophistication in milling equipment and therefore cost regarding patents. At the other end of the scale, low grade can be produced by increasing extraction or, if preferred, making less millfeed. These measures can be used to different degrees.

   One of the difficulties in making divides is the demand for the remaining flours. For example, a significant demand for patent flours of 10% by weight of low ash content while maintaining 90% straight grade may well mean that a certain percent of low grade flour will have to be produced to keep both patent and straight grade flours within specification. The knock-on effect is that either there is a disposal problem for the low grade (little or no market), or the extraction has to be reduced. This leads to loss of money.

   Similar problems can and do occur the other way around. The questions that should be considered regarding divides are the flour specifications required, costing and inventory.

   What are the uses of divide flours? The baking industry commonly uses straight grade flours of suitable strength. For fancy white breads, patent flours are sometimes popular, or even long patents of slightly higher ash. Patent low ash flours tend to be bright in color and lively compared with low grade high ash flours, which are dark and softer. Patent flours also allow production of whiter bread with a finer texture and more pleasing aroma than straight grades.

   Baking quality declines in white breads using flours of longer extraction. Hence, low grade high ash flours are not often used by themselves. It is noteworthy that the highest alpha amylase activity, detrimental to baking quality in more extreme circumstances, is found in the lower reduction flours and in the lowest break flours in particular. The same applies to germ oil content, which is a bread volume depressant.

   Markets for low grade can be found among manufacturers of dog biscuits and general pet foods, as well as other outlets where color and functionality are less critical to product quality.

   All in all, divides are a game that, when played successfully, adds value to the milling of flour. Traps are avoided by first class milling knowledge and careful costing of options.

Origin of flours

 

Ash content

 

(dry basis)

 

Total flour

Flour collecting conveyor 1

     

• top reduction flours

up to 0.4%

 

60%

Flour collecting conveyor 2

     

• top break and middle

     

reduction flours

up to 0.7%

 

30%

Flour collecting conveyor 3

     

• bottom break and bottom

     

reduction flours

up to 1.3%

 

10%

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