Q&As about dry pet food processing

Q: Some pet food producers argue that dry rendered meal has better flavour for pets than the meal that produced from a wet rendering process. What is your view?

A: We at Alfa Laval are not experts on animal behaviour. With that in mind, we will split the answer into two parts:

• Cats are meat eaters with the instincts to catch and immediately eat their prey. They are sensitive to the off-flavours and oxidation generated in the dry rendering system. So dry rendering for pet foods for cats is a definite 'no'.
• Dogs are by nature scavengers and may be attracted to the off-flavours from ill-rendered old meat and meat by-products. However, pet owners consider their pets family members, and longevity is essential. The concerns we have about our food choices also apply to our pets' food. So pet owners choose pet food without trans-fatty acids, rancidity, and burnt proteins to prevent exposing their pets to adverse health impacts. The off-flavour characteristics are better achieved by enzymatic treatments, for instance, in the Alfa Laval HyPro system.

Q: Will water removal create issues due to viscosity of the meats?

A:The purpose of the Alfa Laval Centriflow meat concentration is to produce pumpable fat-reduced, concentrated products. The water phase is concentrated to the maximum viscosity level for the evaporation system, while the solids are treated with enzymes at approximately 40% dry matter to ensure pumpability. The key is pumpability of the water-reduced product. For the fully hydrolyzed product, the viscosity also limits concentration further.

Q: What is the typical fat content in meal from an Alfa Laval Centriflow processing line? Or how low a fat content in meal can Alfa Laval obtain?

A: For a protein meal with 8% moisture, the final fat content largely depends on the raw material and the fat content usually varies between 8% and 15%. With the Centriflow system, proprietary Alfa Laval technologies can reduce the fat content in the produced meal to 6-9% fat, depending on the raw material type and freshness. For Alfa Laval HyPro spray- or roller-dried products, the low fat content levels in meal depend on the acceptable levels of fatty colloidal material for discharge as a separate residue material. Fat can be produced if there is no or low limitations, such as a spray-dried product with 1-2 % fat content.

Q: Can you "over hydrolyze" and negatively effect palatability?

A: Managing the enzymatic process and understanding the palatability aspects is essential in achieving the correct and final diet formulation. The design of the processing system provides an utmost focus on temperature and time control. From that perspective over hydrolyzing is not possible and, therefore, poses no risk of negatively impacting palatability. It is always possible that unforeseen events may occur that adversely affect palatability.

Q: What is a typical mass flow of a three-phase decanter centrifuge?

A: The typical mass flow rate of a three-phase decanter centrifuge depends on the product composition and the size of the decanter. Alfa Laval has solutions operating within 100 kg/h to 30-40 tons/h for a single machine.

Q: Does Alfa Laval conduct tests for customers?

A: Alfa Laval has a test facility where we work with customers to conduct pilot-scale tests, including evaporation and drying of the product.

Q: Some customers claim that parts of bone can block the Twin Screw pump. Can you explain if it makes sense to apply a strainer or filtration device to avoid blockage?

A: Generally speaking, all pumps may experience blockage if the bones or bone fragments are too large. It is therefore essential to adjust the pump design for raw material preparation, including grinding. The Alfa Laval Twin Screw pump technology can handle particles up to 38 mm in size and can process particles up to 2 mm in size in the pretreatment stage of dry pet food production. For the coagulated product in the Centriflow system, it is important to optimize the intermediate tank agitator design to prevent any type of settling since the tendency of coagulated meats is to agglomerate when settling. Agglomeration causes the formation of lumps. These can settle in the pipes, elbows and connections blocking the surrounding piping system and equipment – not necessarily in the pump. For fully hydrolyzed products, the same concerns must apply. Pumping hydrolyzed fish pulp, for instance, can be extremely difficult and resemble pumping a mixture of water and paper clips. Alfa Laval offers solutions to remove bone to reduce the mineral content. We recommend fine grinding to 3 mm.

Q: Is there a difference in the pet food end-product, for different markets? In other words, is there a difference in the requirements for raw materials, in different regions, which result in different demands for technologies ?

A: Alfa Laval mainly sees a difference in pet food segmentation between the basic segment and the premium segment – not regional differences in raw material requirements. Price is always a key factor. The raw material price is not factor when producing premium pet food; processing the right product in the right way is critical. Some premium pet food brands uphold standards of hygiene that are tougher than those used at food processing plants producing meat. Cleanability and sanitation are important parameters when designing process solutions for the premium pet food market. Market segments focusing on price competitiveness rely on temperature and time to achieve exceptional cleanability and sanitation.

Q: Do any antioxidants need to be added to the meat for the Centriflow process?

A: The Centriflow process is designed to process fresh raw materials as quickly as possible. It operates under air-restricted conditions to limit oxidation. However, adding appropriate antioxidants prove advantageous to minimize oxidation during onward handling after the process. The system is also designed to add antioxidants to the product.

Q: Does the digestibility increase with those processes?

A: Compared to a conventionally rendered product, digestibility improves using these processes. It does not, however, provide significant improvements compared to special drying such as flash drying, which alters the structure and enhances digestibility. Digestibility and weight gain is not particularly important for pets. The preservation of functionality, flavours and micronutrients is the key. Here the drying aspect has a significant negative impact.

Q: Can you briefly explain the difference using this process with insects as the raw material instead of meat?

A: The main difference occurs in the pre-treatment. Insects have chitin, a rigid substance that makes up their exoskeletons – not bone. It is important to conduct testing before processing chitin to document the time and enzyme profile required to soften the solids.

Q: One of the presentation slides showed a Centriflow chart in concentrated meat system showing the injection of steam into the decanter separation stage. Please can you clarify this?

A: The Centriflow heating system consists of two stages: (1) the direct steam injection (DSI) heater for raising the raw material temperature from storage conditions to the desired process temperature, and (2) an intermediate balance tank with agitator and steam injection. The tank is the hazard analysis and critical control point (HACCP) for the process to secure a precise temperature before the separation phase in the three-phase decanter.

Q: Why use the concentrated meat process? Why not use enzymatic HyPro processing and then remove more water?

A: The HyPro process secures more water removal. However, using the Centriflow produces three product streams: (1) fat for coating the pellets, (2) the solids fraction, slightly modified, and (3) the highly functional concentrated stick water – a pumpable binder and flavour enhancer for ingredient formulations.

Q: Is it correct to call it meat after the product has been processed to such a level?

A: After introducing the untreated meat to the cooking process, the temperature of the meat increases to well above 100⁰C. As a result, the meat proteins coagulate and release water and water-soluble fat. After extrusion, the pellets undergo drying to evaporate the water. Concentrating the meat this way only rearranges the sequence and may improve the product's properties.

Q: Is it necessary to heat above 50⁰C?

A: At temperatures below 50⁰C, the product will only consist of free water (blood water) and any liquid (melted) fat. Some fat reduction can be achieved. However, reducing the water content to acceptable levels calls for the coagulation (denaturing) of proteins and the reduction of significant amounts of water through evaporation. Increasing the temperature above 50°C is required. The ideal temperature is 95⁰C, enabling coagulation and separation in a few minutes.

Q: Can Alfa Laval provide the enzymes for the HyPro system?

A: Because Alfa Laval is not an enzyme provider, we recommend customers select the best enzyme solution for their products. We will then design the process line accordingly. If required, we will work with international enzyme providers, leveraging their knowledge to identify the optimum solution.