Desiccation is the removal of water from cells or materials, usually by drying, to inhibit microbial growth or preserve food. Without sufficient moisture, metabolic reactions slow or stop, limiting the ability of most bacteria, fungi and other organisms to grow【318303127244670†L330-L360】.
## Explanation
Microorganisms depend on water for biochemical reactions and structural integrity. Drying reduces the water activity of a substrate, creating an environment where enzymes cannot function properly and cell membranes become damaged. In food preservation, drying methods such as sun drying, air drying, smoking and dehydration slow spoilage by lowering water availability. Adding salt or sugar also draws water out of microbial cells through osmosis, further reducing water activity. However, desiccation does not necessarily kill all microbes; some bacteria form resistant endospores or cysts that survive long periods of dryness. Molds and yeasts can grow at lower water activities than many bacteria, which is why dried fruits sometimes develop surface mold. Freeze-drying (lyophilization) combines low temperature and desiccation to remove water under vacuum, producing shelf-stable products while retaining flavour and nutrients【318303127244670†L330-L360】. In laboratories, freeze-drying is used to preserve cultures and biological materials. Desiccators are devices that maintain low humidity environments using desiccants like silica gel. Extremophiles such as halophiles and xerophilic fungi thrive in environments with low water activity.
## Techniques and adaptations
Traditional drying techniques include laying grains, meat or fish in the sun or in heated chambers to evaporate moisture. Solar dryers improve efficiency and reduce contamination. Modern dehydration uses forced hot air or freeze-drying to produce instant coffee, powdered milk and vaccines. In microbiology labs, desiccation is used to preserve culture slides and reagent strips. Some organisms have evolved mechanisms to survive desiccation. Bacterial spores of Bacillus and Clostridium species remain dormant until water becomes available. Tardigrades and nematodes can enter an anhydrobiotic state, losing almost all body water and reviving when rehydrated. Seeds contain sugars and proteins that stabilize membranes during desiccation. Conversely, many pathogens become noninfectious after drying on surfaces because membranes rupture and proteins denature.
Drying is a simple and effective way to control microbial growth and preserve products, but complete sterility usually requires additional treatments such as heat or chemicals.
**Related Terms:** Lyophilization, Osmotic pressure, Water activity, Spore, Halophile