Space foods are processed to ensure quality and safety. Fresh fruits and vegetables are minimally processed -- they're sanitized with a 200 parts per million (ppm) chlorine rinse, air-dried and then placed on a food tray, ready to be stored in the fresh food locker. Some vegetables, like carrots and celery, are packaged in sealable bags. All fresh foods need to be eaten within the first few days of a mission because they spoil quickly.
NASA scientists use certain processing techniques to make foods shelf stable, or safe to store at room temperature. Thermostabilization, or heat processing, extends shelf life to three years. Irradiated foods are shelf stable because they're sterilized by a dose of ionizing radiation. Lowering the pH and water activity of foods can also stabilize them. Freeze-drying, or removing water from foods, inhibits microbial growth, and mold growth can be prevented by removing oxygen from packaging.
Shelf life is determined by noting changes in product quality, and the lab has specific methodology for testing. All foods intended for shuttle flights must have nine-month minimum shelf life. Foods going to the International Space Station must have a one-year shelf life, and any foods developed for future planetary expeditions or outposts must have a five-year shelf life [source: Iowa State University].
Testing at the Space Food Systems Laboratory begins with sensory evaluations. Astronauts rate food by appearance, color, odor, flavor, texture and overall palatability. Foods are then exposed to time and temperature changes, and sensory evaluations are repeated to determine how the foods hold up.
Scientists perform chemical analyses by testing the food's moisture, pH, water activity, nutrients, color and texture as well as considering time and temperature changes.
Packaging materials and methods are developed to reduce contaminates. The materials' weight, shape and waste are also considered during development. Currently, scientists take advantage of materials such as Mylar®, Aclar® and polyethylene to create flexible containers and pouches as well as sticking to old standards like foil pouches and aluminum for cans.
Since food weight allowance is limited to 3.8 lbs (1.7 kl) per person, per day on the ISS, and only 0.5 lbs (0.23 kl) per person, per day on the shuttle, the lab continues to develop new packaging materials to reduce weight and waste [sources: NASA and Iowa State University].
Each package is given a barcode and colored fabric fastener dots. The dots' colors match each crewmember with his or her menu items. Astronauts use the barcodes to log each food item when consumed -- information used by the lab back home in determining future food lists.
Once products and menus are green-lighted, they're given to the Flight Equipment Processing Contractor for processing, packaging and storing before being sent to Kennedy Space Center (KSC) in Florida. Two to three days before launch (or 24 hours for fresh foods), food lockers are placed onboard the shuttle, ready to go into space.
For more information about space food and how astronauts eat in space, visit our related resources on the next page.