History of Milling, Part III

by Meyer Sosland
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What began as a laborious hand operation in ancient times evolved into a highly-mechanized process

by Bryan McGee

Editor’s note: This is the third article in a three-part series on the history of milling technology. The first two installments were published in the April and May issues of World Grain.

The history of milling technology has been one of continuous innovation in pursuit of technical and commercial improvement. Significant changes have occurred from time to time, but even between technological advances, seldom has there been stagnation. Cereal milling and cereal science remain full of promise.

Our generation has witnessed the impact of electronics, which permeate every aspect of this and other industries. We are now seeing the effect of the Internet, which has accelerated the diffusion of ideas and stimulates the worldwide acceptance of new ideas.

This article focuses primarily on the evolution of wheat milling technology during the last half of the 20th century and beyond, which has been marked by the phenomenal advances in electronic control and instrumentation, raising productivity to unprecedented levels. Better control devices and systems, advances in cereal breeding as well as methods and materials of construction have raised quality standards and throughputs of machinery as never before. The use of computer-aided design (CAD) and computer numerical control (CNC) machine tools have accelerated these trends.

However, there have also been some processing innovations that have been of at least equal importance.

During the 1940s, Daverio, a Switzerland-based company, was credited with building the first full pneumatic conveying system using negative pressure to suck the intermediate stocks from the lower levels of the process — mainly from roller mills — to the top of the building. The materials would then fall by gravity to the next machine in the system.

This concept, which dispensed with the traditional cumbersome bucket elevators and horizontal screw conveyors, offered huge advantages that were gradually realized over succeeding years by all of the major milling engineering firms.

The use of pneumatic systems provided much greater flexibility in plant layout and improvements in hygiene and sanitation through the removal of these intrinsically difficult-to-clean conveyors and elevators.

The conveying air also was used to cool the stocks in transit. Removing heat from the process gave an important benefit in allowing much higher roll loadings without the necessity for complex water cooling. It also maintained a negative pressure within the equipment, thus preventing the emission of dust within the plant. A shortage of high-grade timber after World War II accelerated the adoption of metal tubing for mill spouting, which also helped to remove potential areas for insect infestation.

Connecticut, U.S.-based Safety Car Heating and Lighting Company, after carrying out some mixing trials in the 1950s, discovered by chance that the passing of insect infested mill stocks through a twin disc rotor with pins, which they were us- ing for dispersing of material, resulted in a sterile product.

From this discovery, the Entoleter infestation destroyer was derived and became rapidly accepted as a simple, hazard-free solution to a formerly intrinsic problem of insect-derived contamination in flour mills.

At this time, milling engineers found that the higher grinding pressures, as enabled by pneumatic conveying, created endosperm flakes that were difficult to sieve. Simon experimented with the Entoleter device and found it to be an excellent disruptor for reducing the flakes to flour particle size without altering the flour’s characteristics. This resulted in the development of the Entoleter Milling System in the 1960s, which proved particularly helpful for the milling and baking industries in Britain, where "sandwich-type" sliced white bread has long been an important sector of the market.

Higher grinding pressures with smooth rolls could be used to damage the starch cells, which increased the water retention of the dough during the subsequent mechanized baking process.

In the 1960s, Dr. Eric A. Farrand of Ranks Hovis McDougall devised a method to determine starch damage and an associated formula to enable optimization of the grinding roll settings for flour production for the newly introduced Chorlywood Bread Process (CBP).

The CBP, developed by the Flour Milling & Baking Research Association (FMBRA) and introduced in 1962, reduced the proving time required and thus accelerated the baking process by input of substantial energy at the mixing stage. When Britain joined the EEC (now E.U.) in 1974, the use of CBP with flour milled by the Entoleter milling system enabled sandwich-type bread to be made using domestic wheat. Previously, it used highprotein Canadian types, but they were no longer economically feasible to mill due to the high levies applied by the EEC to third-country wheat.

Meanwhile, North American millers, with their access to higher protein wheat, could achieve very high specific throughputs on roller mills with fine corrugations.

Milled products were soon found to be more palatable if the grain was cleaned of husks, stones, sand, seeds and other contaminant impurities. It also reduced wear and tear on the handling and milling equipment. As efficiency of yield and quality became important, there also was an increased emphasis on conditioning or tempering the grain to provide a more uniform and optimized state for milling. The quest for better cleaning methods and preparation of the grain has run in parallel to improvements in milling itself in order to enhance the overall process.

Recently, there has been renewed interest in intensive scouring, peeling and debranning to remove discrete bran layers as techniques have become available. Even today, raw wheat can contain as much as 4% extraneous material that can be removed by one or more of the following principles:
• Size: Flat bed or rotary sieving to remove oversized or undersized particles;
• Terminal Velocity: Aspiration in upward air currents to remove chaff, dust, and other light particles;
• Specific Gravity: "Floating" of wheat off dense impurities by water or air;
• Natural peculiarity: Magnetic or metal detection of ferrous and nonferrous metals;
• Shape: Separation by width or length by use of indents or slots in discs or cylinders;
• Color: Reflected light in the visible and non-visible spectra can be detected by electronic camera devices.

Some of the most interesting applications of these principles during the 19th and 20th centuries have included stone removal by washer and whizzer.

In early machines, pre-cleaned wheat was plunged into the rising side of a screw rotating in a water tank, conveying the wheat to a discharge while allowing the higher density stones to sink. The total immersion had the additional benefit of the agitated water dissolving and washing away mud balls and surface dirt. However, the wheat absorbed excessive moisture.

A partial solution was to feed the wet wheat into a whizzer, where beaters on a rotating shaft propel the wheat upwards against a perforated screen to remove the excess moisture and scour the individual kernels.

The disadvantages of this system included the need for a high level of supervision and maintenance, bacterial contamination of the effluent discharge water and the fairly indiscriminate increase in moisture content.

Developments in the mid-to-late 20th century enabled the replacement of the washer and whizzer by the dry destoner.

The Paddy eliminator, widely used in the rice and oat industries, separated hulled from unhulled kernels by means of an oscillating deck with complex zig-zag compartments, which limited its capacity.

In the U.S., Sutton, Steele and Steele, and in Canada, Kipp Kelly, no doubt inspired by the paddy eliminator, drew air through a sloping oscillating perforated deck. This greatly increased the flow rate of the "floating" wheat stream while stones that remained on the deck were vibrated by the deck in a counter-flow direction. This provided effective dry stone removal for the first time.

The simple dry destoner was superseded by the so-called Gravity Selector, developed by Sangatti in early 1970s. This machine combined stone removal with a facility for concentrating impurities for more intensive subsequent cleaning.

Also in the U.S., studies were carried out by Glen Fisher at Kansas State University that led to the development of the Technovator Grain Tempering Mixer. This machine ensured that water added to a grain stream was uniformly dispersed over each and every kernel. The tempering mixer led the way to provision of a truly controlled tempering system when instrumentation from Chicago, Illinois, U.S.-based Kay Ray was applied. The Kay Ray moisture control instrument incorporated a cesium source to detect changes in density and used microwaves to detect water content to a high degree of accuracy. The Kay Ray equipment was adopted by Simon and was widely used in sophisticated milling plants.

European engineers soon followed suit and developed several alternative intensive dampeners and other devices to achieve similar results. The dry destoner/gravity selector, together with the tempering mixer, finally rendered the washer and whizzer obsolete and further simplified the operation of a modern flour milling plant.

Perhaps the most significant and ingenious invention for removal of injurious seeds, both larger and smaller than wheat, was the disc separator in about 1925 by the Carter Mayhew Company of Minneapolis, Minnesota, U.S. These machines are still in production, having been altered only slightly over the years.

Ernest Simon, later Lord Simon and son of Henry, became a lifelong friend of Howard Mayhew. He licensed the manufacture and introduced the Carter range of all metal wheat cleaning machines in Europe and abroad.

Electronic color separation promises to have a big impact on the cleaning of grain before milling. In the past, this technique has been confined to low-capacity specialist applications but recent advances in sensor and electronic technology combined with significant reductions in cost now make it a viable option for cleaning wheat. The savings in space and energy requirements are considerable.

The concept of removing bran layers before entering the grinding phase is by no means new, but a practical system operating at commercial capacities has proved elusive until recently. Gustav Adolph Buchholz in the 1860s and 1870s was perhaps the first to achieve a credible system. The Surrey, England resident obtained several patents at that time and his successes were described in an authoritative paper presented at a meeting of The Institution of Mechanical Engineers in 1872.

These and similar systems never took permanent hold for various reasons, and the milling industry had to wait until the end of the 20th century to see these aspirations fulfilled on a widespread basis.

As so often happens, two parties were working independently on the problem. Satake in Japan, having decided to enter the wheat milling business, believed they should incorporate their extensive rice pearling and polishing expertise to address the problem.

Meanwhile, Joseph Tkac of Canada, with the support of his employer, Robin Hood, a division of International Multifoods, was working separately on a process that was eventually commercialized as the Tkac & Timm Preprocessing System. In 1990, it was licensed to Robinson Milling Systems as the TrigoTec system. It achieved some impressive technical results but commercial success eluded the system due to its multistage complexity.

Satake spent several years adapting a new range of vertically disposed equipment. Having achieved its own technical objectives, the company set out to refine, optimize and simplify its process to ensure its commercial viability. Initially, it was applied to durum and later, common wheat milling. The Satake processes are known as PeriTec.

Other milling engineers have followed suit and announced their own means of decorticating, pearling or peeling.

Bryan McGee, a milling industry consultant and former special projects consultant for Satake Corp., may be contacted at bryan@bcmcgee.co.uk. We want to hear from you — Send comments and inquiries to worldgrain@ sosland.com. For reprints of WG articles, e-mail reprints@sosland.com.