The June 2021 issue of World Grain included an article, “The Past, Present, and Future of Milling,” written by World Grain Editor Arvin Donley. Milling industry leaders provided their insights covering the history and future of the milling industry. The purpose of this article is to offer some additional thoughts relative to the future of mill design development in the hope that a seed might be planted for future inquiry and development of milling process design and management.
A wheat flour mill, whether it’s in a laboratory mill, pilot mill or commercial mill setting, is basically a fixed processing entity at any one moment in time. Little can be altered with respect to the flow to affect an immediate response in operating efficiency or flour quality. Basically, we can alter the aggressiveness of roll grinding, alter purifier settings to change mill balance as well as material quantity and quality, and alter flour stream selection to achieve specific grade requirements. The available roll surface, sifter surface and purifier width are fixed and cannot be changed without considerable effort and expense. Transport equipment designs between processing points are also generally fixed and designed to carry a narrowly defined flow rate of product with equally narrow material properties.
Long after the startup miller has left the site and detailed operating instructions and guidance are long forgotten, replaced by newly developed habits good or bad (not based on sound facts or scientific method), mill efficiency, flour quality or both begin to drift. The cumulative result generally has a negative impact on mill economics resulting in a call to upper-level technical support within the company or an outside technical adviser.
Depending on familiarity with the original design flow and modification history, the technical adviser leverages experience and background to re-establish the intended mill flow design and makes changes to realign with the available fixed assets. Generally, the quicker issues are identified and corrections made, the better.
Automation, remote process monitoring, and additional responsibilities have distanced the mill operator from the process. Changes with wheat or mill stocks that impact processing are not recognized as a potential cause but are obfuscated by machine and/or processing system status changes. The focus then is not understanding the cause for the system failure but rather getting the system up and running.
Often this approach leads to solving the symptom (system down), not the problem or what caused the system to go down. The lack of data and proper analysis may result in, for example, flow rate reduction to keep the system operating rather than adjustment of roll gap to produce a product that would work within system design parameters.
Wheat is the material processed to produce the finished product flour, yet wheat reduction, separation and intermediate mill stocks are the least monitored and managed components of the milling process. Current mill design and operation appears to assume that wheat blends are inherently uniform and that machine settings establish efficient capital utilization, efficiency, and quality product. Experience suggests individual varieties of wheat have their own “personality” or properties that recalls the nature versus nurture debate surrounding personal development.
The genetics may determine a significant proportion of inherent traits. However, the environment, in the broadest sense of the term, influences the expression of those traits. A given wheat variety, therefore, is not the same when produced at various locations under various conditions of rainfall, sunlight, soil conditions, etc. In essence, wheat varieties and therefore blends exhibit different personalities, properties and behaviors when subjected to similar forces or milling processes. It is the behavior of the wheat and monitoring of the wheat and mill stock properties that may in the future have a greater impact on the gradual reduction process design and management.
Milling wheat on a fixed laboratory milling system reveals hard red winter wheat composite wheat sample personality differences. At the very beginning of the milling process, the feed rate is established by raising and lowering a feeder gate to achieve a feed rate held at ±5% of the target. The range of adjustments to be made is quite significant in some cases and, more importantly, the necessary adjustment to achieve target feed rate results in the inability to pneumatically convey the tempered wheat product to the first break roll. Perhaps an automatic lift adjustment could overcome the problem. Short of that in a commercial mill, the system would be down or operated at less than desired or target load. In the case of the laboratory mill, the load had to be reduced, not a satisfactory action in a commercial milling operation.
Samples show considerable difference in terms of first, second and third break bulk density and resulting bed depth on the sifter media, impacting separation efficiency. Additionally, due to mill design, flow was impeded, and a surge created resulting in a flushing out of the system when load was taken off the mill. The increased bed depth and surge often results in chokes in the transition to the pneumatic pick-up that must be worked around. As someone who has held the position of floor sweeper in a commercial mill, the thankless and non-productive task of picking choke piles off the floor comes to mind.
Wheat personalities also show through in the fixed reduction system processes where flour production shifts downstream when wheat protein is higher or kernels are harder. Flour production occurs earlier in the reduction system when the wheat is softer and/or lower in protein. Might it be helpful to manage the generation across the primary reductions to enhance or customize flour properties such as starch damage or absorption characteristics?
Consider monitoring reduction stock flow characteristics and particle size as well as bran contamination to optimize sifting efficiency and grinding to optimize the milling process efficiency and flour attributes. Differences in these characteristics are observable when milling hard red winter wheat composites. They are exposed when ground stock and flour does not flow freely down a metal chute or across the sieve media. Some samples produce streams and flour that adhere to surfaces with a tenacity destined to result in a choked system at some point.
Wheat personalities really show through in the residue and tail end reductions where bran is concentrated and has been through several passages not yet ready to give up the last bits of endosperm. With some wheat, the bran has remained relatively whole, not creating an abundance of these stocks while other wheat produces copious amounts of bran clinging mightily to the endosperm. It occurs to me that aggressive reduction grinding may have created more compound endosperm-rich bran particles than might have been found with less harsh grinding. Perhaps this topic can be covered in a future article as early milling research has explored this topic.
Bran and the tail over from the last reduction shed light on the nature of the wheat being milled under fixed laboratory mill conditions. Of course, in the commercial setting these streams may be influenced by other issues such as roll setting and tempering conditions. These streams beg to be monitored and responded to with appropriate adjustments for both mill process efficiency and finished product quality.
Focusing on product behavior
Future mill design may benefit by including a focus on product behavior in the systems, not simply machine behavior or previously successful mill settings. Over the years, instrumentation, process controllers and computers along with programs and algorithms have improved process control and process monitoring. More recently instrumentation has allowed improved finished product quality monitoring.
Some headway has been made into process monitoring of granulation or break releases at the early stages of the breaking process but has not been widely adapted. Other properties such as bulk density, the presence of bran, particle shape, flow properties such as stickiness, cohesiveness or even electrostatic properties may prove valuable in process monitoring tools for key stocks.
Millers and mill engineers should be thinking about the future of mill design and should be adapting a behavioral science-type approach to assist developing milling flows to optimize equipment utilization, process flexibility, and product quality. If behavioral analysis can be used with dairy cattle to increase milk production, we should be able to analyze wheat behavior or response to build a better milling process. Will you be the one to use technology, measurements, and analysis to build a milling algorithm that combines machine and wheat optimization?