by Joe Kearns, Extrusion specialist, JPKearns
Consulting, LLC and Director of Sales at Meridian Ingredients LLC
This is a comparison of two different feed preparation processes. A simple comparison and definition would be cooking versus compressing a feed into pellet form with the percentage of cook being at a higher level with the use of extrusion over pelleting.
Material preparation
Let’s review the processes starting with the material preparation before processing. All is the same in terms of batching and weighing until grinding. The possible need for finer grinding exists for the extrusion process. Finer grinding as the possibility to achieve product diameters as low as 0.5mm exist in the extrusion process. Finer grinding is considered important for good pelleting quality also but typically it is not required to get to the 200-micron raw material size. Extruders can make 0.5mm feeds thus finer grinding for extrusion over pelleting. Ground particles should be 1/3 the die opening size for extrusion thus a 0.5mm feed needs very fine grinding.
Processing differences
This brings us to the actual process differences. The feeding system is similar, as both systems need even raw material feeding with volume or weight deliver control. Weight delivery or gravimetric is common on extrusion cooking as it allows for more accurate control of the process additives such as water and steam and other liquids or solids. Why is more accuracy needed with extrusion, simply put the additions by weight give a more accurate pellet characteristic?
Exacting diameters, density, expansion rates for oil uptake, sinking rate and others are controlled by the process and additions. Having stated the above the conditioning systems are usually more advanced on extrusion cookers. Rotational speeds, retention times and mixing effects are controllable for the accurate inclusion and evenness of the preconditioned mass headed to the extruder. This is required as higher levels of liquids are used in extrusion. It is not unusual to add water to be in the mid 30 percent moisture range when extruding some types of aquatic feeds. Pelleting has a liquid or percent water limitation and it is in approximately the 17-18 percent moisture range.
Read the full article in the International Aquafeed magazine online, HERE.
This is a comparison of two different feed preparation processes. A simple comparison and definition would be cooking versus compressing a feed into pellet form with the percentage of cook being at a higher level with the use of extrusion over pelleting.
Material preparation
Let’s review the processes starting with the material preparation before processing. All is the same in terms of batching and weighing until grinding. The possible need for finer grinding exists for the extrusion process. Finer grinding as the possibility to achieve product diameters as low as 0.5mm exist in the extrusion process. Finer grinding is considered important for good pelleting quality also but typically it is not required to get to the 200-micron raw material size. Extruders can make 0.5mm feeds thus finer grinding for extrusion over pelleting. Ground particles should be 1/3 the die opening size for extrusion thus a 0.5mm feed needs very fine grinding.
Processing differences
This brings us to the actual process differences. The feeding system is similar, as both systems need even raw material feeding with volume or weight deliver control. Weight delivery or gravimetric is common on extrusion cooking as it allows for more accurate control of the process additives such as water and steam and other liquids or solids. Why is more accuracy needed with extrusion, simply put the additions by weight give a more accurate pellet characteristic?
Exacting diameters, density, expansion rates for oil uptake, sinking rate and others are controlled by the process and additions. Having stated the above the conditioning systems are usually more advanced on extrusion cookers. Rotational speeds, retention times and mixing effects are controllable for the accurate inclusion and evenness of the preconditioned mass headed to the extruder. This is required as higher levels of liquids are used in extrusion. It is not unusual to add water to be in the mid 30 percent moisture range when extruding some types of aquatic feeds. Pelleting has a liquid or percent water limitation and it is in approximately the 17-18 percent moisture range.
Read the full article in the International Aquafeed magazine online, HERE.
The Aquaculturists
This blog is maintained by The Aquaculturists staff and is supported by the
magazine International Aquafeed which is published by Perendale Publishers Ltd
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