On-line flour testing
July 01, 1996
by Teresa Acklin
Near-infrared technology adds accuracy, reliability to automatic measurement of flour characteristics.
By David Sugden
On-line flour testing is a technology that is here today. It is defined as a process that measures a parameter or parameters repetitiously and continuously over time without limit and produces results locally or remotely for monitoring and/or control upstream.
On-line testing provides several benefits. In a flour mill, the primary objective above all is to provide the customer what he needs — consistently, efficiently and on time. The benefit of on-line testing includes reduction of waste or rework, which always costs either money or goodwill.
In the milling process itself, on-line flour testing has other advantages. An on-line system can warn of problems, confirm satisfactory production, aid in ISO quality management, help control expensive ingredients and allow time for the mill superintendent and his team to concentrate on other areas of responsibility.
Some on-line testing mechanisms have been used over a long period of time. In the mid-1960s, continuous flour color grading was available. Instrumentation still is used for continuous measurements of flour inventories in bins, as well as to weigh flour regularly. In other processes, continuous weighing of wheat has been used, and power consumption frequently has been logged using recording charts.
Newer technologies also have been developed. One example is near-infrared (NIR) techniques, which have become widely used both on line for flour testing and in the laboratory.
Near-infrared technology consists of two types, near-infrared reflectance and near-infrared transmittance. Near-infrared reflectance currently is most commonly used because the transmittance method is not yet reliable enough for some applications, such as whole wheat analysis.
NIR instruments are used to measure flour parameters that include protein, moisture, color, starch damage, ash and water absorption. NIR instruments typically have from six to 12 filters or more, and they operate at different spectral wavelengths.
The laboratory and on-line versions of NIR instruments are the same in measuring principle; the difference is that on-line equipment is fully automatic with its own software, not only for monitoring but also for controlling machine settings or additions of ingredients such as gluten or water.
The one useful test or parameter that is not yet possible using NIR, either in the laboratory or on-line, is that of alpha amylase determination. The only assays currently available are the quick Hagberg system, which can be completed in less than 15 minutes, or the more lengthy chemical assays. The prize for anyone who comes up with a reliable on-line alpha amylase measuring technology would be great, as would that for anyone developing an inexpensive way of reducing alpha amylase activity in flours.
The diagram on page 8 shows how NIR testing is used on four flours from a mill. Each flour is measured, one after the other in sequence, by the NIR analyzer depicted at (1). The four flours could originate from different mills.
In this example, the flow is from the top down. Individual flours pass through a conveyor, redresser sifters, automatic sampler units and then to bins at (C).
The top left flow has a bin of gluten at (A) on load cells to compensate for protein variation by a feedback control loop signal. The top right flow has a moisture feedback control loop, shown at (B), from a water tank with a water control autovalve. The two center flows are being monitored only.
Samples are selected in turn by means of an air conveying line to the NIR analyzer at (1). The sampler unit consists of a small pneumatic cup timed to take material. After measurement, the used sample is returned to a bin at D.
Attached to the NIR analyzer is the personal computer at (2). The P.C. performs numerous functions, including storing considerable amounts of information, providing graphics and trends, monitoring actual figures against targets, providing alarms and allowing operator intervention.
The programmable logic controller at (3) is the link from the mill control room to two-way communication signals. A hard-copy printer is shown at (4), together with a modem computer link (5) for remote troubleshooting by the equipment supplier.
The diagram depicts a comprehensive system. Simpler set-ups are more common, but the diagram illustrates that many possibilities can be arranged.
With on-line systems such as the one shown, protein and moisture measurements are not only accurate, but reliable. One word of caution, however, is that it is critical to ensure that any NIR instrument is calibrated frequently. Calibration is simple, and each equipment manufacturer has his own routine.
Preferably, NIR equipment should be calibrated weekly or even more often. Failure to calibrate frequently can cause serious problems, not the least of which is with the mill's customers.
Less accurate but nevertheless extremely useful, particularly for trend scanning, is NIR instrumentation for the parameters of ash, color, water absorption and starch damage. For semolina, particle size determination with NIR also is possible, although it too is less accurate than protein and moisture analysis.
Two manufacturers focus regularly on supplying on-line equipment, with a number of less well known suppliers also offering on-line equipment. Although the principles of NIR are simple, sampling and sampling presentation to the optics measuring device can be more complex. One manufacturer has a continuously moving stream past the measuring "window," while another uses a stationary and consistently pressed or packed sample against the window.
The popularity of on-line NIR flour testing is justifiably increasing, based on its ease of use, calibration, general reliability, speed and safety. On-line testing also offers the benefit of being neither invasive nor destructive to the product. But to maintain NIR's considerable benefits, it is necessary to ensure proper sampling and sample presentation and to carry out regular calibration.
Potential future functions of on-line NIR technology include the use of fiber optics for remote data transmissions. Other instruments under development include one that measures whole wheat. Many users also have been working with suppliers, unsuccessfully to date, to find a universally acceptable color measurement.
Image analysis in one form or another also is being studied. One system uses fluorescence to determine bran levels, while another uses a charge couple device video camera for the same purpose. These systems show promise both off and on-line and offer the possibility of measuring other parameters as well.
Other devices and methods are possible, but are too far upstream technologically to be commercially attractive, mostly on grounds of cost, if not practicality.
David Sugden, independent consultant to the grain industries, may be reached at The Coach House, Killigrews, Margaretting, Ingatestone, Essex CM4 0EZ, U.K. Tel: 44-1245-352048. Fax: 44-1245-251162.