I accidently left out a steak the other night after cooking for about 6 hours.
It shrunk in size and gained a bit of a tint on the exposed side.
In my pizza eating days, I wouldn't blink twice at leaving a pizza out overnight and eating it the next day for breakfast. But that was loaded with miles of junk. And wasn't steak.
What I want/need to know, if I wish to preserve the sanctity of my grass-fed sirloin, is what's safe? The internet has returned inconclusive ask yahoo results, and I'm certain someone here can break down the science and convince me not to chop up and eat my sadly tainted beef or do so with a reassured mind. (Note: I will not personally hold anyone responsible if I get sick, so be as objective as possible. I am okay with erring on the side of caution, but if I have unneeded worry, I'd rather know so.)
This shouldn't be a problem, so long as your kitchen isn't particularly hot all the time. I've left out cooked beef plenty of times and the only real issue is the exposed surface that dries out. Probably what you are seeing is discoloring on the cut edge due to oxidation or drying out.
I'm not saying that there is zero risk, but remember: when we're talking about beef, the exposed surface is where most of the bacterial action happens. You had just cooked the steak, so the surface had been heated to a hostile temperature for bacteria. You probably also salted the surface, which contains bacterial growth even further. In most cases, spoilage control is moisture control, which is why you can salt and dry beef into jerky by running air over it for 12 hours. I would say heat it up again before you eat it again, but eat with confidence.
EDIT: another poster on this thread told you to use your nose and find out if it still smelled good or developed some funk. This is the correct thing to do. Let your senses guide you as they are better than any time heuristic. I still think your steak will smell steaky, though.
Chance are it's fine, but I wouldn't risk it. I prefer to take the better safe than sorry approach. I know grass fed meat is expensive, but it's cheaper than a bout of food poisoning (considering lost work time, potential doctor or even ER/hospital visits, pain & suffering, etc.).
Personally, if I made it in my own kitchen, I'd eat it. I'd heat it up til it was good and hot and throw it in some broth. If it was in someone else's kitchen or from a restaurant... Not so much. I don't have an iron stomach, but I've eaten food all my life that was set out "European style", since my dad was from a farm town in Sicily and my mom a farmers daughter from Ireland. Both of them were born in the early 1920's, and most homes there didn't have refrigeration. Food, including sliced meats, would be put out on the sideboard at lunchtime, and sit there till dinner at 8, so if the menfolk came in hungry, they'd be able to grab something and go back to work on their own schedule. Purely anecdotal, so take it for what it's worth.
I have never had a basceria-based stomach crisis. Friends have beat me to the punch. Of all the potential weight loss methods, this one is pretty gruesome. Grass-fed cost more, and "sirloin" suggests you shelled out. Let me also suggest that you not risk it.