From the article Medieval Food Preservation - Keeping Food Edible for Months or Years during the Middle Ages :
DRYING FOODS TO PRESERVE THEM
Today we understand that moisture allows for the rapid microbiological growth of bacteria, which is present in all fresh foods and which causes them to decay.
But it isn't necessary to understand the chemical process involved in order to observe that food that is wet and left in the open will quickly start to smell and attract bugs. So it should come as no surprise that one of the oldest methods of preserving foods known to man is that of drying it.
Drying was used to preserve all sorts of foods.
Grains like rye and wheat were dried in the sun or air before being stored in a dry place. Fruits were sun-dried in warmer climes and oven-dried in cooler regions. In Scandinavia, where temperatures were known to plunge below freezing in the winter, cod (known as "stockfish") were left out to dry in the cold air, usually after they were gutted and their heads were removed.
Meat could also be preserved through drying, usually after cutting it into thin strips and lightly salting it. In warmer regions, it was a simple matter to dry meat under the hot summer sun, but in cooler climates, air drying could be done at most times of the year, either outdoors or in shelters that kept away the elements and flies.
PRESERVING FOODS WITH SALT
Salting was the most common way to preserve virtually any type of meat or fish, as it drew out the moisture and killed the bacteria. Vegetables might be preserved with dry salt, as well, though pickling was more common. Salt was also used in conjunction with other methods of preservation, such as drying and smoking.
One method of salting meat involved pressing dry salt into pieces of meat, then layering the pieces in a container (like a keg) with dry salt completely surrounding each piece.
If meat was preserved this way in cold weather, which slowed down the decomposition while the salt had time to take effect, it could last for years. Vegetables were also preserved by layering them in salt and placing them in a sealable container such as an earthenware crock.
Another way to preserve food with salt was to soak it in a salt brine. While not as effective a long-term method of preservation as packing in dry salt, it served very well to keep food edible through a season or two. 1022
Salt brines were also part of the pickling process (see next page).
Whatever method of salt preservation was used, the first thing a cook did when he got ready to prepare the salted food for consumption was soaking it in fresh water to remove as much of the salt as possible. Some cooks were more conscientious than others when it came to this step, which could take several trips to the well for fresh water.
And it was next to impossible to remove all the salt, no matter how much soaking was done. Many recipes took this saltiness into account, and some were designed specifically to counteract or complement the salt flavor. Still, most of us would find preserved medieval food much saltier than anything we're used to today.
SMOKING MEAT AND FISH
Smoking was another fairly common way to preserve meat, especially fish and pork. Meat would be cut into relatively thin, lean strips, immersed briefly in a salt solution and hung over a fire to absorb the smoke flavoring as it dried -- slowly. Occasionally meat might be smoked without a salt solution, especially if the type of wood burned had a distinctive flavoring of its own. However, salt was still very helpful because it discouraged flies, inhibited the growth of bacteria, and hastened the removal of moisture.
PICKLING FOODS
Immersing fresh vegetables and other foods in a liquid solution of salt brine was a fairly common practice in medieval Europe. In fact, although the term "pickle" didn't come into use in English until the late Middle Ages, the practice of pickling goes back to ancient times. Not only would this method preserve fresh food for months so that it could be eaten out of season, but it could infuse it with strong, piquant flavors.
The simplest pickling was done with water, salt and an herb or two, but a variety of spices and herbs as well as the use of vinegar, verjuice or (after the 12th century) lemon led to a range of pickling flavors. Pickling might require boiling the foods in the salt mixture, but it could also be done by simply leaving the food items in an open pot, tub or vat of salt brine with the desired flavorings for hours and sometimes days. 1022