What is freeze-drying?
Freeze-drying is a process that locks in the nutritional composition and structure of the food by drying through the interplay between temperature and pressure, turning the water molecules into vapor (sublimation). This process ensures a long shelf life by removing approximately 98% of the water (more than air-drying) within fruit, but maintains its shape and color. The unique freezing and then drying technique provides a crunchy treat that’s full of flavor.
What does this mean for the consumer of freeze-dried food? The essential nutritious parts of the food remain in a crunchy, shelf-stable form that can be enjoyed anytime, anywhere.
Why freeze dry fruit?
When freeze drying, one completely removes water from the food material while leaving the basic structure and composition intact. There are two reasons someone might want to do this with fruit:
- Removing water keeps food from spoiling for a long period of time. Food spoils when microorganisms, such as bacteria, feed on the matter and decompose it. Bacteria may release chemicals that cause disease, or they may just release chemicals that make food taste bad.
- Freeze-drying significantly reduces the total weight of the food. Most food is largely made up of water (many fruits are more than 80% to 90% water). Removing this water makes the food lighter in weight, which means it’s easier to transport. The food product is now shelf-stable at ambient temperatures, no longer requiring refrigeration. The military and camping supply companies freeze-dry foods to make them easier for one person to carry.
The basic idea behind freeze-drying is to “lock in” the composition and structure of the food product by drying it without applying the heat necessary for the evaporation process. Instead, the freeze-drying process converts solid water (ice) directly into water vapor, skipping the liquid phase entirely.
Freeze-drying is a closed and controlled process. The food is frozen to a specific sub-zero temperature before being placed onto a large stainless-steel racking system inside of a vacuum chamber. The temperature is carefully lowered to below freezing (i.e., -50°to -80°C) while the atmospheric pressure inside the chamber is lowered causing the moisture (ice crystals) inside and surrounding the food product to be vaporized and drawn off onto the ice condenser that lines the vacuum chamber.
The water in the food moves from a solid state to a gaseous state (water vapor) – maintaining the structure of the food and keeping the nutritional value intact. The liquid phase is completely skipped. The moisture in the food product (ice crystals) moves directly to vapor rather than thawing to liquid form.