Food preservation

Food preservation plays a crucial role in ensuring that meals prepared for astronauts in space remain safe, nutritious and palatable over extended mission durations. As space travel often involves long-term storage, limited resupply opportunities and exposure to challenging environmental conditions, a robust understanding of preservation techniques is essential. These methods serve not only to control microbial growth and prevent chemical deterioration, but also to reduce waste, strengthen food security and support environmentally responsible food systems on Earth.

Background and Scientific Basis

Preservation processes slow or halt the biological and chemical mechanisms that cause food to spoil. Microorganisms, enzymatic activity and oxidative reactions are the primary drivers of decomposition, rancidification and visual deterioration. Techniques such as heating, cooling, dehydration and fermentation modify the internal environment of food, making it unsuitable for microbial proliferation. They also stabilise fats and carbohydrates and prevent reactions such as enzymatic browning in fruits.
Effective preservation reduces food waste, lowers production costs and increases the efficiency of modern food systems. It also supports environmental sustainability by reducing the agricultural footprint associated with frequent production, transport and disposal. Many preservation methods are combined to achieve more reliable and longer-lasting results, as seen in the preparation of jams, cured meats and packaged rations.

Traditional Preservation Methods

Many traditional preservation techniques originated long before the advent of modern agriculture. These methods relied on controlling environmental factors such as temperature, moisture and oxygen levels and remain relevant today, including within the specialised context of space food research.
BoilingBoiling is one of the most straightforward techniques for destroying harmful microorganisms. Liquids such as milk and water have historically been boiled to eliminate pathogens. When incorporated into food preparation, boiling both cooks the ingredients and raises their temperature sufficiently to weaken or kill bacteria, increasing storage life.
BurialBurial exploits environmental conditions such as darkness, cool temperatures, lack of oxygen and the desiccating qualities of certain soils. Dry, salty or frozen soil can inhibit microbial growth, making it suitable for preserving vegetables and sometimes meat. Root vegetables, for example, can remain edible for months when stored underground. Cultural practices such as the preparation of sauerkraut, kimchi and even traditional bog butter also demonstrate the effectiveness of burial under controlled conditions.
CanningCanning involves cooking food, placing it in sterile containers and sealing those containers before heating them again to destroy any remaining microorganisms. Introduced in the early nineteenth century, the technique revolutionised food storage, especially for military and maritime use. Canning conditions vary according to the acidity of the food:

• High-acid foods, such as many fruits, require only brief boiling.
• Low-acid foods, including vegetables and meats, require pressure canning to achieve the temperatures needed for safety.

While properly canned food can remain safe for extended periods, spoilage occurs once the container is opened. Inadequate canning can allow the growth of Clostridium botulinum, which produces dangerous toxins without visible or olfactory warning, underscoring the need for precise quality control in space-grade food processing.
ConfitConfit preserves meat through salting, slow cooking in fat and storage while fully submerged in that fat. Historically widespread in Europe, it remains popular for its distinctive flavour and extended shelf life. Though unsuitable as a primary space-food method due to the mass of the fat involved, its principles—salt-based dehydration and exclusion of oxygen—inform modern preservation science.
Cooling and RefrigerationRefrigeration slows microbial activity and enzymatic reactions. Before mechanical refrigeration, root cellars and iceboxes performed this function. Today, cooling remains central to food safety on Earth, though it is less practical in space where ambient temperatures and power limitations require specialised refrigeration units. Nonetheless, the science informs ground-based preparation, packaging and transport of astronaut rations.
Curing and SmokingCuring relies on salt and, in contemporary practice, compounds such as sodium nitrite. Salt draws moisture from food via osmosis, reducing water activity and inhibiting bacterial growth. Smoking adds antimicrobial compounds, including phenols and catechol, which further supress spoilage. Though effective, cured and smoked meats may carry health considerations due to the presence of carcinogenic compounds formed during processing.
FermentationFermentation fosters the growth of beneficial microorganisms that produce acids or alcohol, creating environments hostile to spoilage agents. Cheese, yoghurt, wine and beer are all products of controlled fermentation. Fermentation can enhance nutritional value as microorganisms synthesise vitamins and break down complex molecules. Historically, it also provided safe beverages during periods when water purification was inconsistent. While astronauts do not consume alcoholic products, fermentation remains important in the broader study of food stability.

Modern Preservation Approaches

Contemporary preservation methods adapt traditional principles to meet industrial and space-specific requirements. Astronaut meals typically undergo treatments that ensure stability, safety and acceptable sensory qualities in microgravity conditions.
FreezingFreezing is one of the most widely used preservation techniques for domestic and commercial foods. It halts microbial growth by lowering temperatures below the point at which most organisms can function. Frozen meals retain structural integrity and nutrition well, though they require reliable temperature control. In space, the use of freezers is limited, but freeze-dried foods—items that have been frozen and then had moisture removed via sublimation—are common due to their lightweight nature and long shelf life.
Dehydration and Freeze-DryingRemoving water from food drastically reduces microbial activity. Dehydration by heat is an ancient practice, but freeze-drying is a modern development ideal for space travel. Foods are frozen and then placed under reduced pressure so ice transitions directly to vapour, preserving texture, flavour and nutrients. The result is extremely light and stable food that can be rehydrated quickly aboard spacecraft.
Combined Techniques for Space MealsSpace foods frequently use multiple preservation methods together, such as:

• Thermostabilisation, which uses heat treatment to sterilise foods in flexible pouches.
• Irradiation, which destroys microorganisms without raising temperature significantly.
• Modified-atmosphere packaging, reducing oxygen levels to slow oxidation and prevent spoilage.

These combinations ensure safety even during long missions and offer greater menu variety for astronauts.

Importance of Food Preservation in Space Exploration

Reliable food preservation is vital in space because storage periods may extend across months or years, depending on mission length. Space diets must remain safe under microgravity, resist radiation exposure and maintain flavour and nutritional balance. Packaging must also endure launch conditions, prevent crumbs that could interfere with equipment and allow easy handling in zero gravity.
The principles of preservation directly influence mission planning, ration design and crew wellbeing. Well-preserved foods reduce the need for excessive supply loads, support psychological comfort through familiar flavours and maintain the energy levels essential for scientific and maintenance tasks in orbit or on other celestial bodies.