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History of Pelleting History of pelleting BY DOM CASTALDO REVIEWED AND EDITED BY CHARLES STARK, CASSANDRA JONES, AND ADAM FAHRENHOLZ extrusion process greatly enhanced feed In the past 50 years, considerable changes have digestibility and improved handling, extruders were occurred in the structure of animal agriculture. No expensive and complicated to operate with early longer are agricultural animals produced to any 20th century technology. scale in “back yard” type production settings. Rather, animal production has evolved into a highly According to Pitsch, one of the first successful integrated volume-based business. This is pellet mills was a molding machine in which two particularly true for the swine and poultry industries counter-rotating rollers with pockets, formed and where essentially every phase of production is pressed mash into wafers (see Figure 1-1). The owned and/or controlled by a single entity. wafers had a much lower density than modern feed pellets, which provided no advantage to feed With the wholesale consolidation of the meat, milk, transportation. Also, the mash was not conditioned and egg production industries, feed manufacturing with heat and moisture; therefore, the “wafering” has become more industrialized. Though today, process did not greatly enhance nutrient utilization. there are fewer feed mills in operation, feed production has increased and continues to grow. Figure 1-1. Diagram of a mold type pellet mill. This general shift from on-farm or small- cooperative type feed processing operations to larger industrial-type feed manufacturing facilities has made processing technologies, such as pelleting, more economically feasible. As such, the pelleting process has become a standard feed processing technique. Since the introduction of pelleting in the early 1900’s, the pelleting process has evolved in size and capacity enabling pellet mills to be operated with less labor and greater precision than ever before. The In the 1920s, feed manufacturing equipment following chapter reviews how the pellet process designers introduced the Schueler pellet press has evolved to become a standard feed processing (Pitsch 1990). This design used a spur gear integrated with two rolls (see Figure 1-2). The machine moved mash through indentions in the gear teeth, resulting in a dense pellet. Although this was Pellet evolution an improvement over the earlier designs, the Between 1900 and the 1930s, equipment designers Schueler pellet press was relatively expensive to proposed several feed processing machines, operate and the gear and roll assembly was subject according to pelleting expert Larry Pitsch (1990). to wear. Around 1910, feed manufacturers began extruding feed to increase its value. The extruders conditioned the mash with heat and moisture prior to forcing it through a die plate and knife assembly. While the Feed Pelleting Reference Guide Section 1: Introduction Chapter 1: History of Pelleting Feed Pelleting Reference Guide Section 1: Introduction Chapter 1: History of Pelleting Figure 1-2. Diagram of Schueler type pellet system. through the die holes. Compared to the flat-die pellet mills, the ring-die design had the advantage of quick die change, allowing feed manufacturers to produce a variety of different pellet sizes from a single pelleting system. Pitsch (1990) pointed out that in the first modern ring-die pellet mills, the rollers rotated along the inside surface of the die. However, in later designs, the die rotated while the rolls remained in a fixed position. Other major improvements in ring-die A short time later, the flat-die mill—a machine that pelleting systems have included the addition of a was an immediate precursor to the modern roll-and- second and third roller, greater mash conditioning, die pellet mill—was introduced to the commercial the incorporation of binding aids to feed formations, feed industry. The flat-die mill consisted of rollers larger dies, more efficient coolers and greater power traveling around a vertical axis on a stationary motors (see Table 1-1). Generally, these horizontal die (see Figure 1-3). The movement of modifications have increased pelleting throughput the rollers forced the mash through holes in the die, and pellet quality, while reducing the relative cost compressing the mash forming pellets. Flat-die of the process. mills are still used in the production of some specialty feeds today. Table 1-1. Changes in the power of pellet mills. Year Maximum motor kW Figure 1-3. Diagram of flat die pellet mill. 1930s 22 1940s 37 1950s 93 1960s 187 Mid 1970s 261 Late 1970s 448 1990s 522 2000s 597 2010s 750 During the remainder of the 1930s and 1940s, equipment designers and feed manufacturers focused on using pelleting technology to the In 1928, the first commercial pellet mills were greatest advantage. For example, in 1936, Beacon imported from England to the United States Milling produced pelleted duck feed. This (Schoeff, 1976). The S. Howes Co. sold one of the achievement was important because ducks are first U.S. built pellet mills in 1930 (Schoeff, 1994). particularly sensitive to fines. Other feed companies The next year, California Pellet Mill Company began producing pelleted dog food. In 1946, designed a 22 kW pellet mill that utilized a stainless Wenger Mixer Manufacturing Company developed steel horizontal-plate die. Shortly thereafter, feed a method of producing high-molasses pellets, an manufacturers and livestock producers began to important feed for beef cattle and dairy cows. The recognize the numerous benefits of feeding next year, coarsely ground pellet crumbles were fed pelletized feed and the design which employed a to young chickens for the first time. Crumbles roller inside a vertically-positioned cylindrical enabled broiler producers to obtain the advantages die—the modern ring-die pellet mill—was of pelleting over the entire growth curve of the bird. developed into a commercial machine. In the ring- die pellet mill, the roller forces the mash outward Feed Pelleting Reference Guide Section 1: Introduction Chapter 1: History of Pelleting After World War II, US pellet mill manufacturers pelleting temperatures kill bacterial pathogens, began a period of expansion. California Pellet Mill including Salmonella and E. coli, and deactivate Company built three manufacturing plants in the anti-nutritional factors. In the 1970s, feed United States and began exporting machines to companies were building completely automated Europe. During the following years, several feed mills. Improvements in the control of heat and pelleting technology experts made moisture addition to the mash enabled equipment recommendations on the most efficient operation of engineers to develop steam jacketed conditioners by pelleting systems (Behnke, 2001). the mid-1970s. Jacketed conditioners were used mainly to manufacture high-quality fish feeds (Pitsch, 1990). Century of the conditioner Few pellet mills in the early 1930s had the Table 1-2. Changes in mash capability of conditioning the mash with heat and conditioning temperature (°C) over moisture prior to pelleting. Though it was time. Source: BASF, 2001. recognized that steam conditioning enhanced pellet General Broiler Pig quality, concerns over nutrient degradation, such as 1970 65 68 65 the destruction of the water-soluble vitamins, 1975 66 71 68 overrode the desire to strive to produce a perfect 1980 68 74 71 pellet. 1985 70 76 74 1990 71 79 76 By the end of the 1930s, pellet mill designers began 1995 74 82 79 installing conditioners—originally referred to as 2000 77 86 83 “ripeners”—which added steam to the mash prior to pelleting (Pitsch, 1990). The early mash By the 1980s, pellet mill operators and designers conditioners were barrel-shaped devices. A rotating were focusing their attention on steam quality. Their shaft with various pitched paddles moved the mash aim was to maximize the amount of heat added to forward towards the pellet mill die. Manifolds, the mash—to optimize starch gelatinization, but connected to the feed mill’s boilers, injected steam minimize moisture addition. Excess moisture in and water into the mash. The design of the conditioned mash must be removed post-pelleting conditioner remained largely unchanged until the and tends to plug rolls and dies. The pelleting 1960s. experts at the time moved from using low-quality wet steam, which contained a combination of water One noticeable change in conditioner design over vapor and free water in the form of high-velocity the years has been a steady increase in the suspended droplets or low-velocity drops of water, conditioning temperatures (see Table 1-2). Between to high-quality superheated steam, which contained 1990 and 2000, the average mash conditioning water vapor at temperatures or pressures higher than temperature increased more than it did in the saturated steam. previous 10 years. This difference was likely due to the introduction of high-temperature conditioners A steam harness, which consisted of a separator, such as short-time/high-temperature (ST/HT) regulator and trap, was eventually developed to systems and annular gap expanders, and the ability improve steam quality (Reimer and Beggs, 1993). to add heat and moisture independently to the mash. During the late 1980s, pellet mill system designers developed short-time/high-temperature Modern mash conditioning systems focus on greater conditioners. The aim of the ST/HT conditioners gelatinization of the starch in the grain. Higher was to maximize starch gelatinization, while at the levels of starch gelatinization enhance pellet same time minimizing the retention time of the durability (quality), improve carbohydrate and mash in the conditioner in order to maximize pellet protein digestibility and utilization by the animal output. Also during the 1980s, pellet mill engineers and increase pellet production. In addition, higher focused on steam delivery into the conditioner. One Feed Pelleting Reference Guide Section 1: Introduction Chapter 1: History of Pelleting innovation towards this end was the direct-fired 5). He discovered that 60% of the quality of pellets steam generator, which replaced traditional tube is due to formulation and particle size—activities boilers (McEllhiney, 1987; 1988).
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