January 01, 1997
by Teresa Acklin
Attention to operational procedures throughout the milling process can enhance product uniformity.
By David Sugden
Flour consistency is the uniform manufacture and supply of flour to customers without contamination or variation in any parameter. A parameter consists of the measure of an individual aspect of flour, such as moisture, ash, protein and alpha amylase. Parameters of consistency also include constant weight, labeling and packaging in the case of bagged goods.
The attainment of such variation-free flour is difficult under most circumstances, but careful attention to several influential factors can increase consistency. The benefits of consistent flour lie in satisfied customers with no complaints. On the other hand, it could be argued that intermittent praise from a client actually means inconsistency.
The diagram above depicts the flow of wheat through six blocks, indicated by arrows, representing various stages of the milling process. The dotted lines represent the connection of each stage to the control and laboratory center. Product consistency can be affected by operational considerations in each of these stages.
At wheat intake, as represented in Block 1, flour uniformity is affected by the availability of different wheats and analysis of the differences.
At this stage, physical examination and laboratory tests should be used immediately to assess dockage, test weight, moisture, protein and alpha amylase activity. Contract documents should be compared with these tests to ensure farm producers or other suppliers have delivered within specification. Decisions then can be made to convey wheat to a particular bin or silo after weighing.
Segregation of wheat is the first critical step in attaining flour consistency, and it is good practice to send different wheats to separate bins as much as possible. Segregation enables the miller to blend wheats economically at a later stage, which enhances the likelihood the miller can meet flour specifications with confidence and predictability.
Wheat can be segregated by grade, variety, protein, moisture, Hagberg Falling Number, hardness or other standards. Millers typically combine up to three of these standards, as greater segregation usually is not practical because of lack of bin space.
Precleaning should occur between intake and the wheat elevator (Block 2). The precleaning system should include a magnet to reduce contamination, to protect machines and to guard against dust explosions.
It also is common to have a preliminary damping apparatus on wheat entry to the elevator; this system does not need to be perfectly accurate because more sophisticated equipment will be used during the conditioning stage.
The elevator itself ideally will have first-in/first-out (FIFO) outlets to ensure even quality discharge. At the discharge point, blending weighers or volumetric measurers allow the flexibility to mix wheat for the first time.
The wheat cleaning plant (Block 3) contains machinery that requires daily inspection and occasional adjustment according to wheat type; this adjustment allows the current amount of dockage or screenings to be extracted according to the degree of original contamination.
The wheat conditioning facility (Block 4) should be capable of evening out the moisture fluctuations naturally occurring within and between wheats. This enables consistent tempering times on a daily basis. As with the elevator bins, the conditioning system should discharge through FIFO outlets equipped with weighers or volumetric measurers.
A first-break damper often is located immediately above the 20-minute reserve first-break hopper to toughen the bran just before the wheat enters the primary milling stage. This step enables a lower ash content flour to be milled with confidence.
Milling for Consistency
The typical equipment in the mill itself (Block 5) needs regular adjustment and machine setting after inspection. Furthermore, to assure good constant performance, purifiers, sifter sieves, roll corrugations and dust collectors should be maintained to a reasonably high degree.
The use of additives requires close attention, not only to assure the correct formulation but to guard against cross contamination. Water cooling, if installed, must have constant temperature control.
On line measurement by near infrared reflectance of flour moisture, protein or other parameters is a singular advantage — provided the NIR equipment is calibrated at least weekly or more often. NIR measurement provides continuous charted information and variations in results. What it will not show is the cause of any variations, which is why an experienced mill superintendent or operative is essential.
Most mills have the potential to make one or more divides (see November/December 1996 World Grain, page 26), which are flours of different characteristics made simultaneously. Divides are not as simple to produce as straight grades because they are more prone to variability, and a closer eye is needed during milling to readjust if parameters and yield move out of line.
Product storage (Block 6) encompasses redressing, magnets, weighers, infestation control, bulk storage, flour blending including additives, packaging, warehousing and outloading. It is desirable to have metal detection and rejection equipment, particularly for nonferrous material.
Bulk storage stock control is important because the miller must know the location of his various flours. He also needs to know inventory levels for mill scheduling. A product blending system provides an immeasurable advantage when installed and used to its maximum capability.
Determining the means and options available to assure a high level of product uniformity begins in the control and laboratory center (Block 7), where consistency is measured. The importance of this operational element is best highlighted by using statistics.
A well-run plant will show two-thirds, known as one standard deviation, of test results for a particular flour to be within the experimental error of the measuring instrument. For example, if a protein apparatus has an experimental error of plus or minus 0.2%, the test results of two-thirds of the flour it measures should be within plus or minus 0.1%.
Milling involves a significant time delay that must be considered. The time lag from wheat to flour across the mill alone is at least 20 minutes, more like 24 hours if conditioning is taken into account. So a regular watchful eye on laboratory results will monitor problems before they escalate out of control.
Measurement at each process stage marks the start of ensuring consistency. When discrepancies or variations occur, it's time for checking, rechecking and interpretation.
The top pressure points to watch most of all are the segregation of grain at intake according to test results, careful blending of wheat, conditioning time and moisture, inventory control, controlled flour blending, additives and stock locations and levels — plus good maintenance.
Constant results allow the superintendent to forecast outcomes with a better level of accuracy and therefore confidence.
David Sugden, independent consultant to the grain industries, may be reached at The Coach House, Killigrews, Margaretting, Ingate-stone, Essex CM4 0EZ, U.K. Tel: 44-1245-352048. Fax: 44-1245-251162.