Food preservation, being a focus of my studies in the SCA leads to a number of questions.
The most common question asked of me is that of overall safety. To such questions, my response is that of confidence in the medieval methods.
Methods of Preparation
In cooking manuals, there are a number of methods that are common threads throughout time. (Links to pages on specific pathogens will be added as those pages are finished.)
Covering an item in salt is one of the easiest preservation methods available. This is either done once, with the food being kept in salt, or the salt is changed out several times. Changing the salt in this way increases the drying/desiccating action of the salt. There is also brining, which uses a saltwater solution instead of dry salt to preserve. Bartlomeo Scappi mentions in his Opera that salted foods are to be kept in salt for storage, while semi-salted foods are to be kept in brine.
In De Re Rustica, by the Roman author Columella, one can find a simple pickle. Making this pickle requires only vinegar and brine. Columella indicates a ratio of 2 parts vinegar to 1 part brine. This gives a strong acidity to the final product, helping to ensure safety. While commonly used with a brine, vinegar can be used on its own as a preservative.
The beef jerky enjoyed today serves as an example of drying and smoking. Foods would commonly be hung in/near a fireplace to dry. This smoke imparts flavor, and smokes out any insects or other critters.
Water, as well as air, is required by many food-borne pathogens. The amount of available air and water is limited, by sealing your food in a layer of fat. Pathogens, such as C. botulinum do not require oxygen. Other steps are needed to address such pathogens. The most common step being the addition of saltpeter (potassium nitrate). While it is still used today, saltpeter has mostly been replaced by sodium nitrate/nitrite salts. These sodium-based curing salts provide more consistent results, compared to potassium.
How Safe Is It?
When comparing modern canning recipes with medieval equivalents, the safety is clear. Medieval cooks often went beyond what we now consider what considered safe. Often, a generous hand was used when adding vinegar and/or salt. Meats were often dried until they were hard as wood, often with a salt crust forming during the process.
For more information on food-borne pathogens, click here for my study of Scappi’s “Various salted fowl, preserved in oil and rendered fat”.