Preserving food is not a modern process. Over time, there have been various methods of food preservation in nearly every culture and every period of time. Drying, freezing, curing, fermenting, pickling, canning, and jamming are all forms of food preservation that have been used in the past.  Below is brief description of each:

Drying- This method has been used by the Romans and in the Middle East. It can be done by the sun and wind. 

Freezing- As food is frozen, its molecules lose kinetic energy and slow down. This slows the aging of the food. Some bacteria cannot live in such cold temperatures.

Fermenting- Fermentation was used to make beer as  early as 10,000 BC. Fermentation is done via microorganisms. Some of the microorganism release vitamins, which add to the nutrition of such foods. 

Pickling and Curing- Such methods add vinegar and salt (respectively) to food, which deter bacteria from growing in such foods. 

Canning- Canning keeps food from the air and free of exposure to bacteria. 

Jamming- Greeks and Romans are noted to be the first jammers. At that time, fruits kept in honey was considered jam. It was stored in tightly packed jars. Like canning, this kept food from being exposed to bacteria in the air.