I am having an email conversation with a friend on 7th century dysentery. That got me thinking about early medieval cooking and food related disease. One of the dangers of medieval (and really most pre-modern farming) is fertilizing with manure including human feces.
Three phases of possible food contamination: production, storage, and preparation. That about covers it. So in other words the whole process: contamination in the fields primarily from manure (animal and human), improper storage causes primarily fungal contamination and not washing hands and food during preparation and improper methods is another source. Weather or not human feces was an intentional fertilizer is unknown but its likely that field workers just went in the field.
Letting pigs into a field after the harvest can set up a perfect parasite situation. Humans and pigs share parasites, especially worms, very well. I’m sure it looked like a win-win to early farmers. Pigs root out any remaining nutrition on the field fattening the pigs. They also broke up the ground making it easier to plow and fertilized it with their feces. What they couldn’t see was that pig feces contains worm eggs that make their way to the product and the life-cycle continues in the person who consumed it. No other domesticated animal can make use of a harvested field like a pig. This is probably why pigs have been domesticated just about everywhere in the world except areas where they were considered ritually unclean (like Muslim lands).
The value of the pig still outweighs the infectious disease burden that they bring if the meat is cooked properly and they are managed properly when not in the field. Allowing pigs to roam in the woods, I think, would decrease the chances of them carrying worms in the first place because they are less likely to consume eggs themselves if foraging in the wild.
Even with the best cooking some worms encysted in the meat would get through. These worms would develop into adults in the human host who then passes eggs from their feces. If human feces is used to fertilize crops, then these eggs go back into the life-cycle using both humans and pigs. The cycle can continue completely within humans by poor hand washing during food preparation. Considering pre-modern people rarely washed their hands, we can expect that this would happen fairly often. It would be disastrous for a monastic cook to be infected. Any intestinal disease would be disastrous in a monastic cook; hopefully they had the sense to remove frequently infected people from that job. Some people are more vulnerable to intestinal infections so this would have been an issue.
Most food contamination is bacterial. Animal and human feces normally contains dozens of bacterial species (for each animal it comes from). Many species can cause a mild diarrhea if consumed in a high enough numbers. Some species like typhoid fever cause more serious disease, some of which will be dysentery (bloody diarrhea). Bede recorded that Bishop Eata died of dysentery (dissenteriam) in his Life of Cuthbert.
So how do you handle food to get around all this contamination? You can use osmotic preservatives like salting or preserving in honey. The solute concentration of salt or sugar dehydrates any bacteria and prevents their growth. (Honey is a great antiseptic for skin wounds for the same reason!) One of the problems here is that when the preservative is diluted many bacteria are capable of growing again. This has been a problem in modern times with honey (some cases of SIDS are botulism from honey). Freezing in winter doesn’t clean meat either; it slows growth. As I tell my students, if it goes in the freezer contaminated, it will come out just as contaminated.So we are left with good cooking.
Good cooking obviously depends on what it is. A solid piece of meat should be sterile inside, so it is only necessary to sear the outside of the meat over a fire. If the flames lick the meat, then most of the bacteria should be gone, though I recommend cooking it all the way through. Hamburger has to be cooked very carefully and completely because its been through grinding and processing. It is no longer sterile anywhere. You would have to be very careful with baking or a pit to make sure that the outside of the meat got hot enough and the center cooked well enough, just as you have to be careful today. Honestly boiling would have been the overall safest method of cooking. Given that their teeth may not have been great, boiling had the added benefit of being easier to eat. Raw vegetables would have been the most dangerous, just as they are today. Fruit if picked from the tree or bush should have been safe. The thing about washing food was that the water wasn’t clean anyway unless it came directly from a spring. Wells and small streams can become contaminated with fecal material. Luckily boiling was probably the most common method of cooking, but you needed a good immune system and hardy constitution to survive childhood in pre-modern times.