Its hard to say for a fact, i honestly dont like ground meat at all even when its fresh, but if it tastes fine i would say its likely fine. The only meat ive ever had that i think was bad tasted absolutely terrible, i bought 6 half off grass fed steaks in vacuum sealed packs from tom thumb that were supposed to go bad that night because i was out of meat from my normal supplier, two of them tasted like the most repelling thing ive ever put in my mouth i wouldnt even feed them to my dog i threw them out. I feel like in most all cases your senses can tell you whats not safe to eat, though that might not always hold true. If its bitter than i say get rid of it for sure, i theorize that the steaks fell to imporper temperatures and that combined with the vacuum sealed packs caused the bad growth if they had had air or been colder im sure it would have been fine
