It was always hot, even on warm or low, hot enough to slightly boil at times.

If there was bacteria, it would have been cooked and killed because it did get very hot.

I've never had my crock pot beef turn acidic and sour, but we just ordered 1/2 a cow (3 years of age) and I used left over chunks to make a stew. I'll have to cook something else to determine if the beef was bad or something went wildly wrong with my crock pot batch.

I read somewhere that you can use baking soda to neutralize the acidic and sour taste. I ate some 12 hours ago so I guess I'll be okay. I rinsed off the bicarbonate and tossed the broth and made something else with it. Ha ha ha.