The evolving landscape of extrusion
Pet food has progressed significantly in recent times, with the process of extrusion required to accommodate new developments.
European pet food body FEDIAF reported 10.5 million tons of pet food products sales in 2023. The majority of this is manufactured through extrusion, mainly dry kibble. In what is a constantly innovating industry, the extrusion process needs to adapt to changes in the content of pet food.
Benefits of commercial food
Dry kibble has some marked benefits over table scraps. The food is designed to meet specific nutritional requirements and contains only appropriate ingredients. It is also more convenient to serve dry product from a bag that contains multiple servings and can be stored at ambient temperature for long periods.
Dry versus semi-moist and wet
Dry pet food contains little moisture, commonly between 6-10%. This makes it lighter per meal than semi-moist or wet foods that contain more water: 15-30% and 72-85%, respectively. Transport and storage costs are therefore higher for a wet than for a dry serving.
The higher moisture content also poses a higher risk of microbial growth, requiring mitigation through preservatives in semi-moist products.
Wet food is sterilized after the packaging is fully sealed and deteriorates quickly once opened. Wet food is generally more palatable to pets than dry food. The use of brewer’s yeast and other ingredients that aid palatability is common in dry food.
Raw meat inclusion
There has been an increase in raw or frozen meat materials being added into dry kibble formulations, which then needs twin screw extruders to handle the material.
These higher inclusions are advantageous for labeling, which is based on the ‘mixing bowl principle’. These high-moisture materials weigh in at a higher inclusion and are therefore declared earlier on the label – irrespective that they get cooked and dried down to the finished kibble. The ash and calcium content of raw meat materials is also lower than for meat meals, which again allows for higher inclusions.
However, the high moisture content of such meat materials needs to be transported to the manufacturing plant, which adds costs and in itself gives challenges for contingency planning. The resulting high crude protein content – up to and around 40% – is nutritionally excessive.
Declaration of meat materials
Inclusions of raw meat materials are usually declared as ‘freshly prepared’ and limited to 36% maximum. Together with meat meal, the total meat or animal- derived inclusions can easily exceed half the declared values. This opportunity has seen some brands in a race to the extreme with 75-90% inclusions of animal- derived ingredients. These cases include animal fat, animal digest and fish within the claim.
Claims referencing ‘meat’ or ‘meat content’ can only be made specifically about skeletal muscle, whereas reference to ‘meat and animal derivatives’ encompasses meat and all products and derivatives of the processing of the carcasses of warm-blooded land animals.
Fish and its parts or derivatives would be referenced as ‘fish and fish derivatives’, or more targeted to the species and format.
Allowing sufficient cook
After the raw materials have been mixed, they move to the conditioner to be formed into a dough through the addition of water and steam. This spends a few minutes at a specific cooking temperature. Cooking continues into the extruder through sheer or mechanical energy, pressure and further steam addition. The extruder and conditioner settings affect bulk density and palatability.
After extrusion the kibbles are dried to the final moisture levels, coated and bagged into consumer packaging. The entire cooking process is required to gelatinize starch and denature proteins, thereby enhancing digestibility of the food. It is also the killing step for microorganisms including Salmonella.
Opportunities and limitations
Plant managers become familiar with their specific extruders over time. Manufacturing plants can therefore optimize the unique set-up of their facility. I have heard of extruders struggling with certain levels of gluten or starch sources, whereas other extruders have no problem handling more challenging levels of the same materials.
There are manufacturing opportunities as well in lowering energy costs by choosing materials that improve cooking or reduce drying energy.
The choice of starch source (required for binding) can be decided on with a degree of influence by consumer perception. Traditional sources include wheat and barley, whereas rice is more upmarket. For grain-free recipes, potato, pea and tapioca are often used. Recipes high in meat do not have much space for starch, resulting in dark, dense kibbles due to the lack of expansion.
When push comes to shape
Extrusion is the process of funneling a substance with force through a hole or die, with the shape of the die determining that of the extrudate. Dry kibbles are formed by cutting the extrudate into very short sections.
A different concept, such as textured vegetable proteins (TVP), are also manufactured using extrusion technology. It can make vegetable proteins look like shredded chicken breast, and offers opportunities for fresh, frozen or wet food recipes that want to create a chicken-like appearance in a non-meat formulation.
Configuration matters
The shape of the kibble is targeted to the animal. For example, some shapes are better picked up by the tongue of cats, others are better suited to short snouts. Others can be comfortable for some mouths but in others cause discomfort that can lead to rejection.
More practical considerations include wanting to ensure an even distribution of palatant, or preventing breakage of kibbles due to a delicate structure.
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