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Fig. 1: Freeze-dried strawberries. Source: FrostX.

Vacuum Preserves Food

Freeze drying with the help of vacuum technology

There are several ways to extend the shelf life of food. One of the oldest methods belong of smoking and salting is drying – which was used long before freezing, boiling or vacuum packaging. Freeze drying is a modern extension of traditional drying methods to protect food from spoilage for longer. This process is only made possible by modern vacuum technology because freeze drying food takes place under vacuum. FrostX produces such freeze dryers with small dimensions to make them ideally suitable for bakeries and restaurants. It enables freeze drying of many kinds of fruits, vegetables, herbs, mushrooms, meat and even ready meals.

The process of freeze drying

Freeze drying is a purely physical process that uses the principle of sublimation. Due to the vacuum in the drying chamber, the frozen water sublimates into water vapor. The ice skips the "liquid" state and becomes directly "gaseous" from "solid".

Before the actual drying process, the product must be deep-frozen. The frozen product will then be dried afterwards. After cooling, the actual drying process takes place in the air-tight chamber by reducing the air pressure in the chamber via a vacuum pump until a vacuum of 1 to 0.5 mbar is reached. The evaporation process of the frozen water now starts at -40° Celsius. The water vapor is suctioned out of the drying chamber by the vacuum pump into a downstream condenser. In this "ice trap" cooled down to around -50° Celsius, the water vapor sublimates and condenses as ice on the cooling coil. Most of the moisture is removed from the product in this process step.

During sublimation, thermal energy is extracted from the drying chamber. This means that the temperature in the chamber would drop during this process. The chamber therefore needs to be heated. Care must be taken to ensure that only as much thermal energy is added as is taken from the water as sublimation energy in order to keep the temperature constant or allow a slight increase in temperature.

The drying chamber is then ventilated to atmospheric pressure and the dried product with a water content of one to four percent is removed for further processing. Dry air or an inert gas is used for ventilation so that the dried product cannot absorb moisture from the ambient air.

FrostX freeze dryer with vacuum technology by Busch

The FrostX freeze dryers are smaller than a standard fridge and enable vacuum freeze drying of many kinds of fruits, vegetables, herbs, mushrooms, meat, and even ready meals. All this while maintaining the full nutritional and taste qualities of food. Freeze drying also helps to prevent food waste and makes food storage so much easier, because the durability of freeze-dried food is significantly longer. The compact dimension can fit in even small kitchens or bakeries and the low noise level and reduced operating costs bring even further advantages. Freeze dryers of FrostX are equipped with ZEBRA rotary vane vacuum pumps from Busch Vacuum Solutions. These vacuum pumps are robust and reliable in operation and enable a stable pumping speed even in low pressure range. The vacuum pump itself has a very low noise level and can be easy serviced if necessary.

Even Michelin star restaurants use freeze driers

FrostX just recently delivered one of its freeze driers to a three-star Michelin restaurant in Vienna, Austria. This example shows that the process of freeze drying has arrived in restaurants and enables a whole new way of cooking and taste. And all this without any loss of nutrients and flavor.