A number of topics for this month are energy efficiency in petfood production, starch gelatinisation, preconditioning and in general aquarium feeds. Discussion below can be considered for both extrusion of pet and aqua products.
Energy efficiencies are improving in the various areas of a plant and each area more than likely has different requirements. What might assist in understanding this is every motor has a required duty factor, power, speed/range and torque requirement to achieve the desired requirement. Doing the intended job with the lowest energy cost over time can greatly save on electrical costs. The best bet for this discussion is to ask questions on motor efficiencies for your calculations and project specifications.
Starch gelatinisation, a topic for the ages, is one that was initially judged in non-scientific methods, in fact the first test on this strange, expanded product from Sabetha Ks. At Kansas State univ. was 100 percent cooked method unknown. Recalling back in the day when there was no real easy method to test cook and you had some tested by labs, you reviewed the products accordingly and determined some physical characteristics. Two quick alongside the extruder tests were the kibble stretch test, good stretching of a caught kibble off the die showed good cook. A hand full thrown in a bucket of water caught after the die would swell about two times in diameter thus showing good cook. In today’s standards petfoods have become more complex and thus lab work is generally used in determining the degree of cook. My preferred method was the glucose amylase method of testing. It involved getting a sample and test for total starch and gelatinized starch with enzymes and a water bath. Prep a solution use a glucose analyser and the numbers are used in the equation percent Gelatinized starch/Total Starch X 100 is percent cook. Typical petfoods are in the 90 percent cook range based on this style test which is one of the harder tests to get the desired results. Do a comparison on methods of cook comparison, there are differences. NIR is being developed to do on line or in line testing of starch gelatinization, last search showed they are almost there with this being a predicable method of testing. This would be a big deal to be able to instantaneously reject non cooked kibble.
Another point of view is that advanced computer control is so exact that if you feed the system a raw mix which is predictably reproduced over time and the operational specs are slaved to this formula as well as the physical changes, the die, then the results should be predictable. Note over time extruders wear and if operational specs are saved over their lifetime and used accordingly the same product is produced every time. Backed up with scheduled testing to verify results on cook to confirm.
Preconditioning, the part of extrusion where the raw materials get metered in to begin the process with this area adding liquids so as to have a homogeneous mix going to the actual extruder barrel. Liquids include steam and water and liquid ingredient streams. It is amazing the designs and styles over the years ending up with today’s styles. My personal review, single shafted cylinders constant speed, double shaft counter rotating constant speed, double shafted differential diameter counter rotating variable speed and now double shafted differential diameter with rotation and speed change abilities. What drove the changes in these cases. Mainly how much liquids were hoped to be added and have a flowable product so as to not jam up the downspout due to stickiness between the cylinder and extruder. Retention time was a big factor. Singles about 15 to 30 seconds, doubles about 60 seconds and then the differential diameter versions which took it up into the 240 second range maximum. At preconditioning temperatures and times lysine can be deteriorated if over 240 seconds retention. Traditionally, the old artist operators who had no idea of exactly what was being added into the cylinder felt the product in hand to see if it was too hot to hold and did it kind of form a ball when squeezed. Adjustments made accordingly. Now numeric flow details or computer controls allow for a much more exacting repeatable method of control. In fact, it seems computer control would be mandatory simply from the regulations required to meet FDA requirements, day in and day out, how about minute by minute? Not just flow rates and motor starting, we are talking about controlling in line temperature, pressure with sensors, flow restriction and readings used to automatically change the conditions to meet the immediate results out of the extruder in terms of density and moisture. Cameras can be used to verify appearance.
It boils down to what are the possible losses by not having a computer control system. Hard to give an exact number as it can be calculated in each instance. For me it is obvious, I used to stand there and watch the pile build up on the floor until it was correct and off to the dryer via a belt conveyor or air system. Hundreds of kilos if not tons and now you would be lucky to see 20 litres of waste on startup, same on shut down, the controlled system knows when the conditioning cylinder has emptied and in essence runs until the last possible moment yielding good product.
Back to losses, loss of raw materials on startup shut down and costs associated with rework. Higher percentage of quality product over time. More exacting moistures out of the extruder yields more exactly moistures out of a good dryer thus less shrinkage due to water loss. Quality products less possible returns. Exacting known amounts of energy used in product produced. Lower manpower requirements. In addition, many control system will inform you if the system is not ready to produce due specified line pressures etc. or if a problem develops. Maintenance schedules with reminders and abilities to record data makes computers a real tool in a modern 24 hour a day petfood facility.
As mentioned above on less shrinkage, computer control and dryers and are in the top two of how to increase profits in a petfood plant. Dryers can be computerised but if the moisture variance is not up to standard then no point. Steady state on product in feed rate, air movement, temperatures and bed level are among the top topics when achieving the standard of +/- 0.5 percent moisture variance. Lowering the moisture shrinkage out of the dryer and for every 0.5 percent reduced in a 60,000 tonnes per year plant is 300 tonnes of additional water sold. What is 300 tonnes of finished product worth?
Article contributed by Joseph P Kearns, Editor, International Petfood Magazine
