I came across a crockpot recipe for burritos. It calls for cooked hamburger (1 lb) as one of its ingredients and specifies that I should cook the mixture on low for 6-10 hours. Is this safe? Whenever I have cooked meat in the crockpot in the past I only use a high temperature and I take it off as soon as it is done so its not kept on 'stay warm'. Since the hamburger is already cooked this is not a question on will this cook it properly but more a question on is this safe and how long (max) can I leave hamburger on low?
food is safe so long as the Crockpot is on, and functioning correctly. The food will maintain a simmer as long as its on, which is too hot for bacteria.
I have a version of baked beans I make in a crock pot that cook for 24 hours on low. I've used a thermometer to verify that, once it comes up to temperature, it stays right at a simmer the entire time, which is above the 165F necessary to keep it "safe". I did the verification because of some of the horrified looks I got when I told people that these beans cook for 24 hours and the last 12 is when the changes happen that really make them good.
Basically, the main danger zone is 41F to 140F. If food sits in that range, it's dangerous, and your goal is to get it out of that range as quickly (within reason of course) as you can to maintain safety. If it's colder or warmer than that, you're safe. Unless your crock pot is broken, the low setting is definitely fine.
I would be more leery of the "Keep Warm" setting. That's probably just barely keeping food out of the danger zone, and if it's miscalibrated, it could be holding food right on the edge of the danger zone.
The hamburger meat itself is never going to burn in a crock-pot, and as long as there is a good enough seal and enough liquid, it shouldn't dry out. As long as the meat is in the bacteria-killing temperature range, I don't see why it couldn't stay there for 10 hours.