The Freeze-drying Technology Behind Astronaut Food
There is no such thing as refrigerator or microwaves to store food in the space station. So, how do the astronauts preserve their food for long periods of time in space and maintain their necessary daily intake of calories, vitamins, and minerals? What kind of preservation method is used? Freeze-drying is the answer!
Foods in outer space are mostly ready-to-eat or can be prepared simply by adding water. The freeze-drying process is an elective one for space foods, as it allows nutritional and sensorial qualities to be retained, together with extreme reduction in weight, water content, high solubility, long shelf life at moderate temperature and the possibility to perform rehydration at any desired level (Sharma & Arora 2007).
The stages in freeze-drying mainly consist of pre-freezing, primary drying and secondary drying. Basically, the principle of freeze-drying is allowing frozen water (solid state) in food to sublime into gas or vapor (gaseous state) without passing through liquid state under vacuum condition (0.5 torr – 4.5 torr), thus resulting in food with freeze-dried characteristics such as light, porous product with almost retained original shape and texture (Jennings & Thomas 2002).
The freeze-drying process itself involves the use of freeze-dryer, a machine that provides a large chamber for freezing, vacuum pump which lower the pressure environment of product and support the removal of product moisture content, and collector system as a cold trap to collect moisture leaving from frozen product (Ratti 2001).
During pre-freezing, food is adequately frozen to solid state in order for it to be ready for freeze-drying. Meanwhile in the second stage of primary drying, low temperature and low pressure play a critical role in the sublimation process to remove the ice from the food and produce a dry and structurally intact product. By nature, molecules migrate from area having higher pressure to lower pressure. In addition, pressure is also related with temperature, hence it is crucially important for the product to have a higher temperature than the cold trap. After primary drying, bound moisture still exists (7-8%) in the product even though the ice has sublimed. Therefore, secondary drying needs to be conducted at warmer temperature to reduce moisture content and reach optimum values. At the end of secondary drying, water is desorbed from the product (Jennings & Thomas 2002).
If you do curious and wonder how does astronaut food taste like, then you can simply try to make it yourself at home or at laboratory.
Below is the following video on how to successfully make freeze-dried food at home. All you need is food and a freeze dryer! Good luck with making your own freeze-dried food!
Jennings, Thomas. 2002. Lyophilization: Introduction and Basic Principle. Florida (US): CRC Press.
Ratti C. 2001. Hot air and freeze-drying of high-value foods: a review. Journal of Food Engineering. 49: 311-319.
Sharma NK, Arora CP. 1995. Influence of product thickness, chamber pressure and heating conditions on production rate of freeze dried yoghurt. International Journal of Refrigeration. 18: 297–307.
by Levina Caroline – F24130059