What meats can I serve medium rare and why?
It is generally accepted that pork and chicken must be cooked completely (unless put through a strong curing process) while certain cuts of beef and lamb can be served on the rare side. Why is this?
Are particular bacteria populations present in some animals but can't survive in others? What is the inherent differences between these animals that makes the difference when eating? How can I objectively decide if it is safe to eat something partially on the rare side that does not involve simply trusting the "common knowledge" of the more experienced.
(Don't get me wrong - I appreciate any and all advice that I get from anyone who is more experienced than I am in anything, but I'd like to know how they came to their conclusions).
Add-on to your question: How come duck is always served medium? One would think it would be similar to chicken...
Beef (and Lamb): The surface of beef is often contaminated with pathogens such as e-coli. However, the meat is very dense and the bacteria cannot migrate from the surface into the flesh. Therefore, beef is safe to consume once the external temperature exceeds, 160 degrees F. The internal uncontaminated meat is safe to eat raw.
Pork: Like beef the surface of pork needs to be fully cooked. Unlike beef, pigs harbor a parasitic roundworm called Trichinella spiralis. Infection with the worm is called trichinosis and can be fatal. This worm is killed when the flesh reaches 150 degrees F and is held there for several minutes. Therefore pork is safe to consume when cooked to medium. (Commercial pork in North America almost never has the roundworm present. Almost every case (all?) of trichinosis in the last 15-20 years have come from undercooked wild boar or bear meat). Trichinella spiralis can also be killed by freezing (time and temperature dependent).
Chicken: Almost all chickens have Salmonella or Campylobacter present on the surface (at least). However, chickens have a less dense flesh than pigs, sheep or cows. Therefore, the bacteria can migrate deep into the flesh. Also, the processing of chickens is much more invasive than the previously mentioned animals which also means the interior meat can get contaminated. This means the meat must be cooked to well done throughout.
Duck: With duck it seems to come down to a matter of processing verses chicken. Also, they are raised in a much less confined manor, which helps prevent the spread of pathogens. There is still a chance of getting a salmonella infection from undercooked duck but cooking the breast well done basically ruins it, so people take the (small) risk.
Ground meat: Grinding meat, by its nature, implies the surface and the interior is mixed. Therefore, one must assume the meat is fully contaminated and must be entirely cooked to well done.
Interesting info, I never heard of these things. Do you have more in-depth links for "chicken meat is less dense"? Also, the sentence "almost all chickens have salmonelly or campylobacter" sounds improbable, do you have a source? (I agree that campylobacter is a common bacterium, but I would expect it on other meats too. Salmonella infected chickens are not that common, as far as I know).
Bacteria found in 83% of chickens (http://www.usatoday.com/news/health/2006-12-04-chicken-bacteria_x.htm). 37%–51% Campylobacter in Canada (http://www.cmaj.ca/content/177/6/570.full)
Chicken meat is less dense than beef or pork (http://busycooks.about.com/od/cookinglessons/a/foodsafety.htm). Not the most authoratative source, but I could not find anything else that explained why cooking the surface of chicken meat would not follow the same reasoning as beef.
I suspect it's not really "density" but fat content; ducks are fairly fatty and fat tends to protect pretty well against bacteria, but chicken is very lean. Farming/confinement and simple popularity may also be a part of it; I think duck is a lot less likely to be contaminated, and being less frequently eaten, there's no reason for farmers to try to mass-produce it on the same scale as chicken.