Time to turn up the heat in feed processing?
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by Detlef Bunzel and Andreas Lemme, Evonik, Germany
elleting is a core process in compound feed production for feed mill operators as it increases bulk density and stabilises the mixture. The resulting uniform particle size improves storage and handling properties which, in turn, also means lower transportation costs for mill operations. Compacting feed also enhances its nutritional value by increasing energy density and preventing selective eating. Animals are unable to avoid or reject individual ingredients, due to changes in palatability if components in the diet are altered for nutritional and/or cost reasons. This reduces waste, losses and production costs for farms. Alongside achieving these benefits, operators must ensure they are meeting food and feed safety requirements. In Europe, Regulation (EC) No 178/2002 lays down requirements for feed safety in Article 15: 1. Feed shall not be placed on the market or fed to any foodproducing animal if it is unsafe. 2. Feed shall be deemed to be unsafe for its intended use if it is considered to: • have an adverse effect on human or animal health; • make the food derived from food producing animals unsafe for human consumption.
Pellet quality, as well as size, should therefore be a key issue for operators. Studies have shown that feed formulation (40%), particle size distribution (20%) and mash conditioning (20%) have the highest impact on standards. If we assume formulation and particle size distribution are constant in the production process, conditioning of the mash is the most significant process variable that feed mill operators can influence to improve the quality.
Chemical preservatives are subject to restrictive regional regulations (e.g. 70/524/EG in the European Union), so heat treatment is a focus for feed producers when reducing and controlling bacterial contamination of feed mash in the production process. Equipment manufacturers have developed several approaches to deal with this challenge. All of them consider conditioning temperature and time as relevant parameters for the successful reduction of bacteria in the process. By inducing more thermal energy into the mash, mechanical influence factors, such as changes in raw material properties and particle size distribution, can be better balanced in the compacting or pelleting process.
Adapt conditioning according to formulation
In feed production, a wide variety of raw materials and formulations are pelleted. With raw materials of agricultural origin, handling and processing properties vary over time based on provenance, weather conditions during growth and harvest, preprocessing and storage conditions, as well as shelf life. Besides bulk density and particle size distribution, humidity or water content is the most prominent physical property affecting feed processing. Among chemical properties of raw materials, protein, fat and starch contents, as well as ash and fibre contents, have the most impact on nutrition and processing. Researchers and feed mill practitioners have found approaches, over the years, to address different physical and chemical properties of raw materials in diets by adapting the conditioning process. Assuming that inclusion of liquids is defined in the diet, theoretically the only parameters that pellet mill operators could adjust besides the feed rate would be steam pressure and temperature. As a rule of thumb, approximately 0.6 percent of dry steam added
26 | June 2019 - International Aquafeed