When astronauts leave for a mission, they will not be able to refrigerate their food, so anything they take along must be nonperishable. The space food that they bring must also be easy to eat without making a mess, since the astronauts will be outside the gravitational field, and any crumbs could float around and get stuck in equipment or in the astronauts' eyes. Because astronauts will often be in space for weeks or months at a time, they are usually unable to bring fresh food, such as fruit and vegetables, on board the craft.
Many types of space food are dehydrated, or freeze-dried, and sealed. When an astronaut is ready to eat, he or she can add water to rehydrate the meal so that it will be edible. Though there is no refrigerator on board a spacecraft, there is an oven, so astronauts are able to heat up or bake their meals as necessary.
While in space, astronauts generally use flour tortillas for sandwiches, rather than bread. This is because bread can have a lot of crumbs, which will float around in the vehicle. For condiments, ketchup, mustard, and mayonnaise are provided in their standard forms, but salt and pepper are provided only as liquids, because the powdered version would be likely to float away.
Today, a wide variety of menu items are available for astronauts as space food. They can choose from meals including beef stroganoff, chicken teriyaki, and turkey tetrazzini. Typically, an astronaut will have the chance to decide his own meals from a menu list well in advance of launch.
Food is provided in disposable containers that can be attached to the astronaut's meal tray, which is strapped to his lap, so that the containers do not float freely in space. The astronaut must consume each part of the meal separately, not starting on another course until the previous one is finished. Once the meal has been eaten, the packaging must be disposed of and is put into a trash compactor to eliminate waste.
In recent years, some chefs have begun to experiment with creating meals for astronauts. Celebrity chefs, including Emeril Legasse and Rachael Ray, have designed meals that have been offered on space flights.