While the final freeze-dried food product might look similar, there are differences in the equipment used and the required food safety processes between freeze-dried foods prepared at home and those prepared by a food manufacturer in a processing plant. These differences are why you will find a wider variety of commercially prepared freeze-dried foods than those made and sold as cottage food products.
Freeze-drying equipment
At-home freeze-drying units are small and typically able to process 5 to 10 pounds of “wet” food at a time. “Wet” food means raw or cooked food that has not been freeze-dried. At-home units have pre-programmed settings or standard profiles that do not allow the home user to make adjustments. Some at-home units will allow the home user to add extra drying time. Testing of the functionality of at-home units has shown fluctuations in the temperature which can have an impact on the sublimation step.
Freeze-drying equipment used by food manufacturers is much larger. A pilot scale unit can process 20 to 50 pounds of “wet” food and is typically used for product research and development. An industrial or batch unit can process 250 to 4,000 pounds of “wet” food. Pilot and batch units have continuous monitoring systems that measure the temperature, pressure and time, recorded by a data logger system.
Processes and recipes
Freeze-drying is considered a specialized process. A food manufacturer uses a customized recipe for each product. The recipe and procedures are reviewed by a process authority to ensure product food safety. A process authority evaluates the product's formulation steps, the final water activity, and packaging materials and steps. A challenge study and shelf-life or stability study for each product may be needed. A challenge study is when a food is intentionally contaminated with illness-causing microorganisms and their survival and growth are monitored throughout the food manufacturing process.
A food manufacturer will also develop a HACCP (Hazard Analysis Critical Control Point) plan that is reviewed by a regulatory authority before production begins. The HACCP plan details how the food manufacturer will minimize food safety risks throughout the entire process.
The National Center for Home Food Preservation has not yet published any research-based recipes for those making freeze-dried foods at home. Validating freeze-drying recipes is a challenge due to the differences in at-home freeze-drying equipment. However, several universities are conducting research to develop safe recipe guidelines.
Want to learn more?
Check out the freeze-drying food page to learn about the process and science behind this food preservation method. Review how freeze-dried foods and ingredients can be used in cottage foods.
Have a question you want answered?
Email your questions to the food safety team at exfdsafe@umn.edu. It may be featured in this newsletter to benefit all Minnesota cottage food producers.