Jan 2, 2024

VACUUM MICROWAVE DRYING: AN ALTERNATIVE TO FREEZE DRYING

PART 2 – RAPIDLY DRY WITH MICROWAVE

In part 1 of our series, we briefly outlined their drying techniques and end-products. While both operate at low temperatures with vacuum, freeze drying is a longer three-step process that requires freezing, followed by two heating steps. Vacuum microwave drying on the other hand is a relatively simple and fast process with one drying step. This allows for better preservation of original material appearance. As a result, it is ideal for applications where retaining the original material appearance is crucial, like producing fresh-looking single ingredient dried fruit snacks.

In part 2, we’ll discuss their processing time, potential system configurations, energy efficiency, and energy sources.

TIME

Processing time fluctuates for both methods depending on the material, but generally speaking, vacuum microwave drying is a faster process. It can be completed anywhere between 10 minutes to 2 hours. Whereas freeze drying takes between 10-52 hours depending on the material. This is because freeze-drying is a slow three-step process, that risks the final product quality if rushed. For instance, shortening the freezing stage could result in uneven freezing, and ultimately uneven drying in the material. While trying to speed up the sublimation stage could risk causing the ice to melt rather than sublimate, potentially leading to a loss of nutrients, flavors, and aromas.

OPERATIONS

With regards to energy, both are electric emission-free drying technologies that may require little to no installation of services (like gas lines) compared to gas powered systems. Although, freeze drying is more energy intensive as it requires about 50% more energy than vacuum microwave drying. This is because freeze drying is a slow process that requires freezing the material, followed by two long drying phases. While vacuum microwave drying is a rapid and energy-efficient one-step process, and the majority of the energy is absorbed by the material.

Both techniques operate at relatively low temperatures and in an oxygen-free environment to preserve material quality. Freeze drying is often used as a single drying step in a production process, but vacuum microwave drying can be used as the single drying process or in combination with another drying method (like freeze drying) for pre- or post-processing. Adding vacuum microwave drying to an existing drying process can be ideal to potentially increase throughput and energy-efficiency (and lower emissions if added to a process that uses natural gas).

In terms of systems, both methods have closed systems that can capture any volatized components due to their vacuum pump. Freeze-dryers are often continuous or batch tray-based systems that require a larger footprint and more space. Vacuum microwave systems are compact machines that can be manufactured based on the client’s material and processing needs. For example, they can be continuous or batch systems with tray- or mixer-based material handling.

CONCLUSION

Both techniques offer low-temperature drying, ideal for emissions-free processing of food materials. Although, vacuum microwave drying is a rapid process that’s faster and more energy-efficient compared to freeze drying. This is because freeze drying is a long three-step process that can take more than 2 days. Whereas vacuum microwave drying is a relatively simple and fast process that can usually be completed in less than 2 hours. Ultimately, the choice between drying methods depends upon the material, processing time, operation parameters, and end-product goal.

CURIOUS ABOUT DRYING YOUR MATERIAL?