In both the food and pet food industries, ensuring that products are safe for consumption is a top priority. One of the key methods used to achieve this safety is the "kill step"—a process designed to eliminate harmful pathogens like bacteria, molds, and viruses that may be present in raw ingredients. Freeze drying, a preservation method widely used for both human food and pet food, is not only effective at preserving nutrients and flavor but can also play a crucial role in meeting the kill step requirements. (The Freeze drying process itself is not a kill step. The Parker units allow for a kill step process to occur but it’s no longer Freeze drying when that occurs.)
The "kill step" refers to the treatment of food (or pet food) to eliminate pathogens, typically through heat treatment. This is vital for preventing foodborne illness, particularly in products that may be contaminated during processing. In most food processing, this step is achieved through methods like pasteurization or sterilization, which use heat to destroy microorganisms. For instance, the food industry generally targets a 5-log reduction in pathogens, equating to a 99.999% reduction in microbial load.
However, some products, such as freeze-dried foods, require different methods for achieving this safety level, all while preserving the integrity and nutritional value of the food. Freeze drying, with its combination of freezing and low-pressure conditions, has proven to be highly effective in achieving this goal.
Freeze drying involves three primary stages: freezing, primary drying (sublimation), and secondary drying (desorption). These stages not only preserve the structure and nutrients of the food but can also be adapted to kill harmful pathogens.
Freezing: The first step in freeze drying involves freezing the food or pet food product to temperatures well below freezing, typically around -40°F to -50°F (-40°C to -45°C). This step helps to lock in the food's cellular structure and nutrients.
Primary Drying (Sublimation): After freezing, the product is placed under a vacuum, and the temperature is gradually raised. This causes the frozen water in the food to sublimate, meaning it transitions directly from a solid (ice) to a gas (water vapor), leaving behind the dry product. During this stage, the food temperature may range from -10°F to +50°F (depending on the material), which is a critical point for pathogen control.
The temperature and vacuum conditions during this phase can be fine-tuned to ensure that harmful microorganisms are destroyed. Studies have shown that the combination of low temperatures and the vacuum conditions of freeze dryers can be enough to reach the required pasteurization levels without the need for direct heat.
Secondary Drying (Desorption): In the final phase of freeze drying, the product is gently heated to remove any residual moisture. This phase typically occurs at temperatures around 120°F to 160°F (49°C to 71°C). While this heat is lower than traditional pasteurization methods, it’s often sufficient to kill off any remaining bacteria or pathogens in the product without compromising its structure, texture, or nutritional content.
The pet food industry has increasingly turned to freeze drying due to its ability to preserve the natural nutrients in raw ingredients, while also offering a safe way to eliminate pathogens. Pet foods, especially those with raw or minimally processed ingredients, are particularly vulnerable to microbial contamination.
In the freeze drying process for pet food, manufacturers can carefully control the temperature and time spent at each stage to ensure that the food reaches temperatures high enough to kill harmful bacteria like Salmonella and E. coli. The controlled environment allows freeze drying to effectively meet the safety requirements of pet food products without using high temperatures that could degrade nutrients and flavor.
For example, raw pet food products that are freeze-dried may undergo primary drying at temperatures low enough to ensure that the texture and quality remain intact. In the secondary drying phase, temperatures are carefully raised to levels that can safely eliminate pathogens, achieving the kill step and ensuring the food is safe for pets to consume.
While traditional heat treatments like pasteurization and sterilization are commonly used in the food industry to achieve the kill step, freeze drying offers several advantages:
Preservation of Nutrients: Freeze drying is gentler on nutrients compared to traditional high-heat methods. Vitamins, enzymes, and other sensitive compounds are better preserved, which is especially important for both human and pet food products.
Retention of Texture and Flavor: Freeze drying maintains the original texture and flavor of foods much better than other preservation methods, making it ideal for high-quality, raw, or premium pet foods.
Reduced Risk of Overheating: The low temperatures in freeze drying reduce the risk of overheating, which can cause the food to lose its appeal or nutritional content. In contrast, conventional heat methods may degrade essential nutrients or alter the food's texture.
Freeze drying is an effective and versatile method for not only preserving food and pet food but also ensuring the elimination of harmful pathogens through the kill step. By controlling temperatures and pressure during the freeze-drying process, manufacturers can achieve the necessary microbial reduction to meet food safety standards, all while maintaining the product's nutritional integrity, texture, and flavor. Whether for human food or pet food, freeze drying offers a reliable and safe alternative to traditional heat-based methods, with the added benefit of producing shelf-stable products that are nutrient-dense and ready for consumption.