Discussion on dogfoods of different styles in the editorial and the addition of liquid containing ingredients such as meats, slurries, steam, fats or oils and water is a topic for further review. There are many different extruders in production with various designed conditioning cylinders. Singles, doubles, differential diameter and combinations of these feeding into the extruder and possibly with various levels of speed controls. The goal of preconditioning is to add liquids elevate the temperature while still having a free-flowing material continuously feeding the extruder inlet.
Sounds easy until you push the limits and having witnessed the limits conditioning was changed based on feeding the inlet, too wet and gummy did not allow long even production run as the downspout would block over. Temperature was not really an issue but the surface moisture on each particle results in uneven flow when higher moistures were attempted. Retention time became the issue which allowed time for moisture uptake from the surface into the particles yielding a more predictable even flow. An additional benefit was even heating from the added steam. Now add some fat and or meat and you are back at hard to flow mass out of the cylinder. More adjustments and effective methods developed to achieve a reasonable amount of meat and fat added in an extruder and flow evenly to the extruder barrel. Fat and water reduce friction in an extruder designed to cook in this fashion. Therefore, friction needed to be increased in order to handle the elevated difficult to cook ingredients. The extruder barrel needed to be adjusted with more disruptive cooking elements located in the barrel.
Any disruption in extruder barrel flow increases friction. Combinations of shearlocks, cut flight screws, screw volumes and end of barrel flow restriction devices allowed for smooth production up to about 20 percent fresh meat added. Combine these changes with variable speed screw adjustments allowed for the specifical mechanical energy inputs to handle these formulas. Fat could be added in the lower teens without much effect but as higher levels of these moisture and slippage ingredients were used then product densities increased. A whole new class of petfoods evolved. Twin screws showed that they also could be configured to do the same with an additional five percent meat or about 25 percent total added in the process.
Trying to reach higher levels in a frictional extrusion device became more difficult thus heat exchanger designs have allowed for even higher levels of meat to be added in an extrusion process. Conditioning also had to be elevated in order to handle higher moisture levels. As moisture levels increased there was a point the kibble was strong enough to exit the die but still a bit weak for handling thus gentle systems to reduce the moisture before the finish dryer developed. Plant designs and meat handling systems to keep the unprocessed meat separated from the finished extruded product area developed with pumps and sanitary system to inject the meat directly in the extruder conditioner. These precautions and GMP’S, good manufacturing practices, and SOP’S, standard operating procedures, are needed in plants where FDA rules of bacteria control would be in effect.
Published in the April 2024 issue of International Pet Food.