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Steam Conditioning in Feed Pellets Processing

Steam Conditioning in Feed Pellets Processing
Along with grinding, conditioning is one of the most important factors in achieving good physical quality of feed pellets. Conditioning creates thermal, chemical and mechanical energy; the steam used during conditioning disrupts the structure of the starch and causes gelatinization and also plasticizes proteins and softens fibres. The process of gelatinization creates natural ‘glues’ which allow the feed particles to compress tightly and adhere to each other when passing through the pellet die. Optimal ‘cooking’ of feed will result in more durable feed pellets and reduce levels of fines.

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In most cases, the main problem with achieving maximal efficiency of pellet mill is quality of steam. Steam conditioning of the pellets is about the application of heat and moisture. You must apply the right amount of heat and moisture in order to produce the best quality pellets.
The most effective mean of moisture and heat addition to the feed is using dry saturated steam. Because dry saturated steam consists mostly of vapor as opposed to wet steam which consists of free moisture. Wet steam transfers its heat less efficiently (lower enthalpy of evaporation) than dry saturated steam and can cause uneven moisture distribution in the mash, resulting in choking or slipping of the pellet die. Dry saturated steam has been shown to increase mash temperature by 60 ºF (16°C) for every 1% added moisture, while wet steam increases mash temperature by 56 ºF (13.5°C) for each 1% increase in moisture. It has also been shown that poor steam quality can reduce conditioning temperatures by 43 ºF to 52 ºF (6°C to 11°C), depending on the amount of added moisture.
Effect of steam conditioning
A poultry layer-diet was used in experiments to determine the effects of steam-conditioning level on pelleting variables. Dry pelleting was compared with steam conditioning (to 65 and 80° C) before pelleting at both constant and maximum production rates. Temperature rise of the material being extruded through the die and electrical energy required to pellet showed that steam decreased mechanical friction during pelleting. Pellet durability and percentage of fines from the scalper showed that steam improved pellet quality. Pressing the mash through the pellet die caused more starch damage during dry pelleting than during steam pelleting. Starch was not damaged during the steam-conditioning process. Total energy required for pelleting (electrical plus steam) was highest for the 80° C treatment. However, steam conditioning allows increased production rates and improved pellet durability during handling and transportation of finished feeds.