Wheat starch and Gluten Manufacturing

by Teresa Acklin
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Flour millers should consider several factors before expanding in this area.

By David Sugden

   If anyone thinks flour milling is difficult, he should try wheat starch and gluten processing.

   What makes this processing so comparatively difficult? Starch and gluten manufacturing is a wet process, which means an excess of water to flour is used to make a slurry or batter.

   Those who know maize starch manufacture, a well known technology and the major starch source worldwide, will appreciate the greater subtleties of wheat starch. And while maize offers a major profit opportunity in maize oil, wheat offers a greater one in gluten, in terms of both value and tonnage.

   Gluten has unique functional properties that are used principally in breadmaking. It is also used in pet foods and breakfast cereals, although substitutes are available for the latter. But gluten carries greater price volatility than maize oil because it often is traded internationally and is subject to supply and demand influences.

   Another principal difficulty with wheat starch and gluten manufacturing lies in separating the two because each has very different physical properties. Gluten is awkward to extract from a parent flour because of its rubbery stickiness.

   A major factor in any decision to build a wheat starch/gluten factory is the market for its products. Such a factory manufactures six main products, as seen in the accompanying diagram: "A" (or primary) starch, gluten, "B" (or secondary) starch, solubles, bran and germ. The market must be able to support competitively the profitable disappearance of these goods.

   The uses of "A" starch are found foremost in the fine paper and food industries, where low protein maize starch and farina (potato starch) compete. Modified starches can also be derived for either industry.

   In the fine paper industry, "A" starch is used for sizing. "A" starch also is incorporated in many varieties of food and is used as a feedstock for ethanol production and conversion into glucose syrups. In some countries, "A" starch is sold in wet or slurry form and transported in tankers. This cuts out the need for drying to a powder.

   Gluten today is sold as a powder, although in the past it was common to trade it in wet form in some countries. "B" starch is marketed in the adhesive and corrugated paper industries, as well as for food. Solubles are marketed in syrup form for ruminants.

   The input for a starch/gluten facility is wheat and flour. The nature of the particular wheat flour will vary from location to location depending on wheat variety, quality, price and availability.

   Typical yields from a wheat starch process will be between 50% and 54% of "A" starch at less than 0.4% protein, 8% to 12% of gluten at 75% protein, 6% to 10% of "B" starch at less than 1.2% protein and 14% to 20% solubles at up to 4% protein, all expressed on a dry basis. But yields can vary considerably from these examples.

Process Technologies

   The technologies used for wheat starch and gluten separation have evolved from the early Martin Process. This was essentially a flow starting with a stiff continuous dough, not too unlike the continuous dough processes popular in the United States in the 1960s and 1970s.

   The problem with this system was the large amount of process water used (more than 15 parts of water to one of flour), the length of time taken to complete the process, a tendency for the gluten to begin to devitalize through the working of the dough and the relatively small capacities of fewer than five tonnes per hour. Effluent was a big problem, creating treatment costs at the sewage plant, and energy costs were high.

   A milestone breakthrough came in the late l970s with the patented Raisio Process. The essence of this process was the observation by the Finnish inventors that a centrifuged slurry of flour and water produced a layer: "A" starch first, gluten next, then "B" starch and lastly solubles.

   While this characteristic was well known, the Finns used this knowledge for the first time in wet processing. They came up with the clear concept to separate the constituent parts in their natural sequence of specific gravity.

   Other companies and workers have devised in-house systems that are not dissimilar, the objectives being to maximize yield and product purity while minimizing water usage and therefore energy.

   Technologies have advanced with the advent of various batter, rather than dough, methods. Capacities today reach well over 40 or 50 tonnes per hour of flour, using water to flour ratios of 2.5 to 1 or better. Also, processes now are self-contained in that material does not disappear down the drain, which helps prevent environmental problems.

   The flow illustrated in block form in the diagram includes wheat flour milling as part of the starch/gluten manufacturing facility. This is not strictly necessary, but the objective of producing starch/gluten from wheat flour clearly is better served by a dedicated flour mill.

   Of course, economics is a factor. If an existing flour mill close by has sufficient spare capacity, then why build another one?

   On the other hand, a flour mill under the total control of the wet processor means that extraction and particle size can be optimized. What is more, wheat supplies can be sampled and selected according to best advantage.

Process Specifics

   In a dedicated flour mill, typical flour yields will be around 76% to 78% with an ash content of 0.8%, dry basis. For starch/gluten processing, flour characteristics are important.

   Protein content generally should be higher rather than lower because that will give higher gluten yield and therefore financial gain. Gluten values vary between U.S.$600 and U.S.$1,600 per tonne, compared with "A" starch at U.S.$200 to U.S.$400 per tonne in powder form. Gluten powder moisture content is around 8% to 10%, with "A" starch at 12% to 13%.

   Ideal flour particle size will be up to 180 microns, whereas most flours for bread and baked goods are fewer than 130 microns. The larger particle size reflects less grinding, which keeps the damage to starch content down. This in turn enables a sharp separation of gluten and starch during the wet process, resulting in a finished gluten that is high in protein and an "A" starch that is low in protein.

   Alpha amylase activity also should be kept low for the same reason. The Hagberg Falling Number on the 7 gram per 25 milliliter test should be greater than 160, preferably higher.

   If excessive alpha amylase is present, the centrifuge and hydrocyclone separators within the wet section have to deal with undue foam; this causes clean separation difficulties, producing too high a protein in the "A" starch — greater than 0.4% up to 0.6% dry basis. This may well be unacceptable to the market, especially to the fine paper industry that is accustomed to the 0.3% protein consistently found in maize starch.

   After the milling process, flour is mixed with water, homogenized and fed to a decanter separator. This machine produces "A" starch for refining and dewatering, gluten and "B" starch for separation and solubles.

   A series of recovery and reprocessing runs for product purity are necessary in the plant, which is built with stainless steel. Fiber screens are strategically placed to dispose of branny particles.

   After the "A" starch is refined, it is dewatered and dried in a straightforward flash dryer of the single pass type and stored prior to shipping in bulk or bags. The "B" starch is handled similarly.

   Gluten is different in that after dewatering, it is dried by a so-called ring dryer because of the need to keep gluten vitality at its maximum when reconstituted with water. The gluten ring dryer works on the principal of a ring, loop or almost closed circuit where the heavy, still damp particles are flung to the outside of the ring for redrying. The lighter fraction of finished gluten is bled off by a valve to a bag filter, storage and packaging.

   Solubles are put through a multistage evaporator and concentrated to a thick syrup form typically for sale as animal feed. An option is to produce methane gas by anaerobic digestion techniques. The solubles fraction contains principally suspended protein, fibers and pentosans.

   Another important factor in starch/gluten processing is the regular need for bacteria control. This is carried out by a regular "Cleaning in Place" system using sodium hypochlorite, which is filtered and recirculated. Cleaning frequency should be at least every three weeks.

Quality and Economics

   The quality control laboratory attached to a starch/gluten plant must measure many flour characteristics, especially protein content, alpha amylase activity, ash content, particle size and starch damage. Moreover, the laboratory should be able to quantify the likely yield of products using the centrifuge test; for example, some wheat flours will have a high gluten-to-total-protein ratio, whereas others will not. If the starch/gluten plant has a mill attached, the laboratory also must test incoming wheat.

   The laboratory also will compare finished product measurements to specifications. Gluten, for example, normally is sold at 75% protein, dry basis, or even as high as 80% (higher proteins are essentially impossible). The remaining 20% or 25% is made up mainly of starch material and fat, and if gluten protein tests high, it is possible to blend starch or flour to meet a lower specification.

   In starch/gluten processing, the biggest cost factor by quite a degree is the cost of the raw material, be it wheat or flour. In the European Union, wheat is normally more plentiful and cheaper than maize; accordingly, wheat starch and gluten processing today is overtaking maize starch in the European Union.

   In the United States, where maize normally is more plentiful and cheaper, maize starch is the principal product. Canada and Australia are large wheat producers and also have major wheat starch industries.

   Remember that wheat starch extraction is some five times greater than gluten — even though the revenues are roughly equal — and the personnel skills needed are very different from flour milling in certain respects.

   Starch/gluten manufacturing is much more of a chemical process, needing a constant watch of plant parameters, yields and qualities, and process staff are trained differently from millers. Salesmen with knowledge of starch users and uses are required to move a considerable amount of product at the best prices. The laboratory is usually more extensive than that of a flour mill because of the greater number of variables.

   All in all, wheat starch/gluten processing is an exciting and fascinating, if volatile, business. The market for the various products demands careful local research and assessment together with identification of well qualified people who understand the technicalities and financial consequences.

   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.