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The importance of extrusion and some history
Roger Gilbert asked that I share some of the changes I've experienced over the years and what is in the future in terms of the importance of extrusion technology with an emphasis on nutrition and safety. That is a lot in a short article. When I started over 40 years ago not many people knew what an extrusion cooker was.. We had to convince the industry it was a possible production method for many products. Pet food was the predominate industry and was ever changing. In these cases, the process required proof of its ability.
Can an extruder run for 24 hours and not stop making good product?
Sometimes, but what happened when it did not do as intended? It was hard work figuring out what the situation was, you would listen to the machine, as it would talk to you and point out the error in your assumptions. This is back in the day when screw profile development was the area needing improvement. Screw buildup, product sticking to the screws, was just one area and preconditioning. Modern day extruders are equipped to handle all current existing possibilities without burnt product or the stickiness associated with inferior preconditioning. Single screw advanced profiles and twin-screw designs have eliminated this effect along with modern preconditioning practices. As you can imagine, extruders were operated manually, it was an art, understanding what was going on and what to do to get the desired product. There were only so many things you could change in the old days; water and steam input to the conditioner or barrel, dry feed rate and barrel temperature were the main options. If you can imagine putting indicator pointers on valve handles so you could see and record the fractions of a valve turn on steam inputs. Water rotameters were used so you had an idea of how much water was added. Operators did not work 24 hours a day so you had different conditions with each operator; they all thought they knew what was best. Controls changed slowly but the quantum leap was computer control, the point where extrusion turned from an art to a science. Everything could be set and flows controlled over a production period, even on the night shift. Dryer advancements occurred after the extruder control developed giving an even-ness in many aspects to the product out of the extruder. The deficiencies of dryer designs became obvious. It used to be three to four percent moisture variance and now it is in the 0.5 percent range, greatly improving profitability as well as product quality. Currently the industry has inline measuring devices allow for instantaneous data on the product density and moisture advancing control again to a new level. Other aspects can also be
measured greatly improving the extrusion technology. The topic of safety covers many areas, mechanically and the safety of the product in terms of quality comes to mind as the top two. Ever see a die come off the extruder based on extreme pressure buildup? Engineering designs allowed for improvements to safely increased power input for increased capacities. How do you ensure the salmonella is eliminated in the product? Much advancement in both areas over the years has occurred. Experience of being the initial developer of the technology resulted in many trial and error situations and feedback from loyal customers that generated the vast development of this technology backed up by attentive engineers solving and advancing the designs. The system can determine temperatures, hold the product to achieve a set point, usually 77 degrees centigrade is of interest, the point salmonella is eliminated. Specific Mechanically Energy can be controlled automatically with the in-line sampling devices and thus density control of products and the cell structure, porosity the product, for oil up take. Complete new designs exist to allow ultra-high fat or meat inputs in the extruder. Amazing products in the pet treat arena are made by extrusion, which started by simply making a brown and round pet food. Advancements in the pet food and aquatic sectors closely followed each other as they usually had similar situations; solving one solved them for both areas. Human foods also have made vast improvements over the years. Expansion of the products made and their quality were demanded and tested. Water holding capacity in textured soy or meat replacements, breadcrumb processing with an eye on the freeze and thaw and frying cycles. Starch modifications are a story all on their own. Shapes, varieties of colors as well as filled products are all made by extrusion for breakfast cereals and snack foods to mention a few.
What is the future of extrusion?
It seems endless; I am having a hard time thinking of one good challenge that was not achieved. Extrusion is a very versatile process, specialised machines made for exact processes or highly versatile designs that can do it all are available. As users of extruders or if you are interested don’t be bashful, ask and you just might receive what you are after, I can visualise the developments are just around the corner for your soon to be imagined product of the future. Examples would include engineered ingredients, the use of byproducts combined to make ingredients of superior quality. On the nutrition side, amino acids such as methionine, lysine and taurine can be attached to the normally included vegetable proteins in a feed or when creating an engineered ingredient when pumped into the process using the extruder as a production system and reactor to create the bond. Good luck and keep up the good work.
Joseph P. Kearns Retired from Wenger Manufacturing, Inc.
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