1) Curing:
The earliest form of food preservation in history is perhaps the curing of various foods, particularly meat.
The process involves the dehydration of liquids via drying, smoking, and salting the meat in specialized rooms.
The meat was hanged and after it was salted, it was left out to dry.
With that, people managed to get rid of potential bacteria and preserve the food longer.
It was mostly consumed during the winter season, as foods became scarce.
2) Cooling:
Before the invention of the refrigerator as a place to freeze foods to preserve them, people harvested ice.
The ice was then stored in special ice cellars, or any room where the temperature would be a constant of 0 Degrees Celsius or even below.
It was typically used for beverages, but later people used it to freeze any sort of food that was not already cured, which allowed them to cook it later for consumption.
3) Boiling:
Boiling was used typically for water and milk.
To get rid of bacteria, people would heat water or milk to their boiling point, or the temperature at which the vapor pressure of the liquid was equal to the pressure exerted on the liquid by its surrounding atmosphere.
As the water was the staple for various cooking recipes in cultures, people often boiled their foods as they cooked.
4) Heating:
The most commonly used method of food preservation is perhaps heating itself.
At high amounts of heat, the various foods placed in the pots were rid of bacteria, therefore, this method was mostly used when preparing stews and soups.
5) Sugaring:
As sugar cane was brought into Europe via trade, it allowed for yet another process of food preservation.
Fruits were at first dehydrated and later placed in jars filled with boiled water and sugared either with crystalized or raw sugar (or any natural liquid with high sugar density such as honey, molasses, or syrup).
These jars would later be kept in storerooms and before they were going to be used, they would be fermented.
6) Pickling:
Pickling was the counterpart of sugaring; only it was used for vegetables instead.
This process was used to store foods in an environment where bacteria could not reach and infest them.
People would put the vegetables in jars, which contained boiled water, brine, vinegar, alcohol, or vegetable oil.
Yet at times, the water was not boiled, allowing for the bacteria inside the jars to produce organic acids and become preservation agents, most typical of which was lactic acid that was formed during the fermentation process.
7) Lye:
Requiring a strong stomach to muster the foods after they were exposed to lye, allowed for the preservation of foods by making them too alkaline for bacterial growth.
The lye also converted the fats in the food, changing their color, flavor, and texture as well.
8) Fermentation:
Used specifically for artisanal foods: alcohol, vinegar, olives, bread, and cheese.
This process allowed specific acids produced by some bacteria to enrich the flavor, texture, and color of the foods and act as preservation agents, disallowing other forms of bacteria to infect and cause damage.