Before humans evolved from hunters and nit-pickers to farmers, we have always stored food and drinks for different reasons. Regardless of the varying reasons for storage, we generally want them to be fit for our consumption.
Over time, preserving farm produce has always been a challenge for human beings. We live among billions of organisms, especially insects and microbes (bacteria and fungi) that feed or live on anything organic. Microbial activities on food and farm produce result in bio-degradation, food poisoning, pollution, loss of value etc. Living things are exposed to chemical activities around all around that can alter the state of organics.
For instance, sunlight can trigger an oxidation process in chemicals that are found in food, converting them to chemicals that are not fit for consumption. However, nature has devised a way of protecting plants and animals from these degrading agents, such as microbes and sunlight. Melanin as an example is a natural colour pigment, secreted by the human body to protect humans from the damaging effects of ultra-violet rays from the sun. Plants and fruits have hydrophobic, protective layers (cuticle) that serve as defensive barriers to various biotic and abiotic stresses.
A fruit or vegetable with a cut will rot faster than one without a cut because the penetration of microbes is made available. When fruits and vegetables are harvested, or when animals are slaughtered, they lose these protections; they become defenceless to bio-degrading microbes and chemicals, which immediately become active on them, till the point of rot.
The higher the moisture content of a vegetable, fruit, seed or slain animal, the higher the chances of losing such a product to decay and waste, because microbial activities are higher in moist environments. Also, the greater the lipid content, the faster they become rancid, as a result of oxidation, mainly caused by exposure to sunlight.
To store farm produce or food for a long time, they have to be artificially protected from microbes, oxidizing chemicals and sunlight. To do this, factors like heat, light, moisture, mechanical stresses, microbial activities and chemical contamination must be controlled. Over the years, methods have been discovered and adopted in controlling these factors. These methods range from thousands of years (traditional) to less than fifty years old (modern). In most cases, these methods are combined to get a desirable result.