Reviewing a few of the articles in this issue it is interesting to see the development and advancements in the post-biotic arena.
It is mentioned the stability for production systems and thus an increase in heat stability is suspected to be improved greatly. Millions of metric tonnes of petfood are made by a wide variety of extrusion designs and most are good at cooking thus heat generation, reducing heat lability in this product in an advancement needed. This leads into one of the topics this month, conditioning.
Conditioning also known as preconditioning is the area of an extruder that begins the process. Dry and liquid ingredients are metered into the pre-conditioner starting the process. Moisture and steam are the major liquids added but other liquids can include fat, digests as well as meats and liquid ingredients to control Aw, water activity, when making semi moist petfoods.
Basically, a preconditioner is a continuous mixer where a shell or tube surrounds rotating beaters or paddles with a dry material inlet at one end and liquid injection ports located along the conditioner with a discharge on the down steam end. What happens between the inlet and discharge is the science of material preparation for extruding petfoods and other materials. Mentioning other materials as an example, corn curls or balls, extreme high-pressure extrusion to yield 50 gm/l density requires virtually no water added and if it is added in the inlet of the extruder is sufficient for production thus no needed preconditioner. Not so with petfoods, high- capacity medium shear extrusion requires proper high-quality preconditioning to achieve the desired product and associated profitable capacity.
The style of petfood being made can be limited to the abilities of an extruder to make that petfood so determining the effective operational ranges is an important factor for your petfood production mix. Reviewing the styles available, single shafted preconditioners are not as popular now as they initially were due to limitations of capacity, moisture input and non-interruption of the flow which would improve mixing. Series of single shaft cylinders form multiple level preconditioners. This staged approach allows for various sets of conditions in each level. Higher speed for mixing, lower speeds to increase retention time. Double cylinders came into the picture and in one cylinder retention time and ability to increase moisture levels improved. Longer retention times allowed for moisture to be absorbed better and thus a huge reduction in a sticky mess between the cylinder and extruder inlet.
Differential diameter designs where the shafts had different diameters and speeds yielded a huge increase in ability to mix thus more meat could be added and flow homogenously out of the cylinder and into the barrel, most important for long continuous operation or running time. Improvements on this DDC design continues and elevating the abilities to new heights, CVs of right at 3, couple this with water and steam injection with improvements of eliminating escape of free steam. Couple this with controls to signal acceptance to discharge based on use of inline sensors for mainly a preset minimum temperature.
We would not be seeing improvements in preconditioning if it was not effective. Historically, trends were for increased flexibility of ingredients use in extrusion and the conditioners coupled with barrel designs have fulfilled this need. The use of liquified meats, vegetables, fruits and any other liquids formulators are considering is increasingly possible. Overall system designs can result in limitations on the moisture levels allowed in the extrusion process. Standard extruder designs would usually operate in the mid 20 percent moisture ranges. As more energy and flow restrictors are used in the barrel coupled with matching the ability of conditioners the limits are upward with flexibility in non-traditional ingredient use. New systems exist with thermal cooking techniques where moisture levels approach 40 to 50 percent of the formula, high meat inclusion products.
Another topic of interest is shaping. The act of cutting the product out of an engineered and specifically design orifice to give a specific product shape. What can be done with die holes is amazing and interesting. Allows for production of unusual shapes if desired. When making general standard petfood the goal is perfectly shaped high capacity across the die face. There are guidelines for this in terms of open area per tonne using the desired final density and expansion rates based on the starch source and percent inclusion in the formula. These high-capacity product are usually sold for less per kilo then the exotic and unusual shapes usually due to the fact that the intricate dies automatically reduce capacity to make an acceptable product, quality of shape of the final product. Also, these advanced shapes usually have a more expensive formula, could be elevated meat and fat levels coupled with non-traditional starch sources.
Recycling under processed material is not unusual due to the cost of raw materials. Typically, this material which mainly comes from the extruder start up from the cylinder by pass and the die until the product is judged to be acceptable. Years ago, the product was sent to the dryer and a marker was used to determine when to collect the product out of the dryer to continue back to reprocessing. This allowed the dryer to dry the material out of the die and thus be reground and reincorporated in the mixing area. Developments with controls and the idea of why dry the materials, why not just put in a tank of water soften it up and have a solids content of approx. 10 percent. Pump this into the cylinder as you are adding water in any case and the rework is handled right at the extruder. Typically, a small amount is generated with today’s computer-controlled machinery. However, a 40-kilo collection of startup waste over a year, as an example, 1000 startups is 40,000 kilos of waste. Worthy of interest based on cost of the ingredient, the additional handling, drying, extra bin for rework and all associated with handling this material. It is contained in the processing area and leaves only when it passes through the extruder and reaching same temperatures for bacteria elimination. In conclusion systems not only handle the waste but use water from the head jackets as make up water, preheated, it also can create a vacuum to control the free steam from the atmospheric pre-conditioner and die knife area. Simply makes the extrusion area much cleaner, an all- around benefit.
Article Contributed by Joseph Kearns, Editor, International Petfood Magazine