The food that an astronaut ate some decades ago is very different from what it is today. In the early space-travel years, they ate dehydrated, paste-like food that was preserved in tubes and consumed through straws. However, in today's space age, they eat food in the same way as people do on Earth, the only difference being that it is sealed and packaged properly.
Astronauts are able to prepare and eat a variety of foods in space. Some can be consumed in their natural form, like fruits, while some need water to be added to them, like spaghetti or macaroni. Moreover, a forced-air convection oven is also provided in the space shuttle for them to be able to heat the food before eating it. However, as there are no refrigerators, the food has to be prepared and consumed without storing it for a long time. The style of eating in space is no different from the regular one, which includes opening the food packets using a scissor and consuming the food with a fork, knife, and spoon.
There are seasonings like ketchup, mustard, and mayonnaise available in the spacecraft, to add flavor to the food. Salt and pepper are provided but in a liquid form, as they cannot be sprinkled due to the absence of gravity, which will simply cause them to float away. There is also a possibility of them clogging the air vents, spoiling the equipment, or entering someone's eyes or nose.
Astronauts eat three meals a day which include breakfast, lunch, and dinner. However, they also consume some snacks periodically. The US space agency NASA has found that their diet reduces by about 70% when on a space mission. Nutritionists have ensured that the space food provided to them is capable of supplying sufficient vitamins and minerals to them. Calorie needs can differ from person to person, like a short woman may need around 1,900 calories a day whereas a tall man may need around 3,200. They have a wide range of foods to choose from like nuts, chicken, beef, seafood, and candies. The meat supplied to them is prepared in such a way that it absorbs sauce and mustard, which prevents dryness. It is also exposed to radiation before packing to preserve it for a longer time. The food packages are designed in a way that makes them flexible and easy to use. Drinks like coffee, tea, juices, fruit punches, and lemonade are also available.
Astronauts also eat high-protein cereal snacks, or dry fruits like raisins, almonds, and cashew nuts. They can also request some particular foodstuffs that they would like to carry with them, before the shuttle launch. Those foodstuffs that are permissible are given to them to take along. When it comes to disposing the meal packages, they are thrown in the trash compactor which eliminates waste.
Nutritionists and chefs are always experimenting and trying out different space foods that can be served on space missions. Space missions have progressed greatly in this aspect.