By: Editorial Team Reading time: 4 Minutes


Freeze-drying for health

Active pharmaceutical ingredients and the vitality of bacteria cultures remain intact for extended periods: freeze-drying is an indispensable conservation method for the pharmaceutical and biotech industries. And liquid nitrogen is ideally suited to provide the required cooling.

Anyone bitten by an animal should absolutely get vaccinated against rabies. And fortunately, this also works after the fact! For people who work in veterinary medicine or spend a lot of time out in the woods, preventive vaccination and regular booster shots are recommended. In both cases, the vaccine takes the form of a white powder that protects against rabies viruses. It can be stored for years in a normal refrigerator and is available for use as needed immediately after dissolution in water. The key to the extended shelf life of the rabies vaccine is freeze-drying, also known as lyophilization: for many vaccines and pharmaceuticals, it is the optimal method to enable simple storage and to prolong effectiveness. It is also used to conserve laboratory samples, starter cultures, blood components, membranes and biocatalysts.

As a natural component of the air, nitrogen is not subject to the strict regulations applied to refrigerants.

Hubert Sell, Head of Design for Hof Sonderanlagenbau

Freeze-drying units from HOF

In the freeze-drying segment, Messer has been working with the Hessian mechanical engineering firm Hof for many years now. It is one of the leading providers of freeze-drying systems for pharmaceutical and biotechnical applications. The company’s product portfolio ranges from small devices for laboratory needs to large vial and bulk units for production.

Using ice to make steam

Freeze-drying relies on the physical process of sublimation. In a vacuum, the frozen water contained in the products transitions directly from the solid state to the gaseous state, because the boiling or sublimation point of the water falls along with the drop in pressure. The product loses its moisture without having to be heated to high temperatures or subjected to long, slow drying. In so doing, ingredients and cell structures remain practically unchanged. In the first step, the substance is deep frozen at normal pressure. This can be done using refrigeration equipment much like freezing food in a freezer. Another frequently applied method uses liquid nitrogen (N₂) as a source of cold. It serves both to freeze the product uniformly on the trays of a freeze-drying unit and in the further drying process to draw off the released energy generated as the water vapor resublimates into ice in the condenser. The liquid nitrogen evaporates with the cooling of a secondary circuit in a heat exchanger. The cold from that circuit is then used to freeze the active ingredient. Larger ice crystals cannot form or damage the cells. “Other benefits of liquid nitrogen cold include the simple process control, practically zero noise emissions, and the low maintenance requirements of the plant, which does not need many moving parts and provides extremely highly reliable operation,” says Hubert Sell, Head of Design for Hof Sonderanlagenbau.

Gefriertrocknen mit Stickstoff EN/Freeze drying with nitrogen EN

Located in the town of Lohra in the Hessian region of Germany, the mechanical engineering firm with nearly 300 employees specializes in, among other things, the design and manufacture of freeze-drying systems for the pharmaceutical and biotech industries. “As a natural component of the air, nitrogen is not subject to the strict regulations applied to refrigerants, which often contain hydrofluorocarbons that are harmful to the climate and whose use will be banned completely by no later than 2030.” But its list of strong points doesn’t end there. Since it needs no active refrigeration equipment, a nitrogen-based system is much more compact and has a much smaller footprint. Its operation requires less electric power and less cooling water, which can be important arguments depending on the existing infrastructure and building statics. Huber Sell adds: “And last but not least, a nitrogen unit features the lowest investment cost in terms of building services – above all when the existing building already has a nitrogen supply – as well as low maintenance costs.”

Freeze-drying of food

Freeze-drying was invented by the Incas and the Aymara in the High Andes, long before the Spaniards arrived there. They set out potatoes at night at about minus ten degrees Celsius, used straw insulation to keep them cold during the day, and let them dry out in this way over a long period of time. The highly shrunken spuds had a virtually unlimited shelf life and were easy to transport. Once swollen in water, they became a nutritious meal again. These are the same benefits that also speak in favor of freeze-drying food today: with dramatically reduced water content, food is well preserved, weighs much less, and is easy to transport and store. Drying in a frozen state conserves the ingredients and the cell structure. Once water is added, freeze-dried food closely approximates the fresh version. The process is used for, among other things, coffee, instant beverages, muesli fruits, spices, emergency rations and astronaut food.