Cold brew souring that fast usually comes down to how clean the pitcher was, not just the time on the counter. Any milk protein or old coffee oil left in the corners feeds bacteria way quicker than people expect, so even a 12 hour batch can turn if the jar wasn't scrubbed well. A vinegar rinse before each batch has kept mine from going off, and it also fixes that weird stale taste that shows up after a few days in the fridge. Two days on the counter is still a gamble though, so the fridge method is the safer call either way.

Been there, mine tasted like regret with a splash of disappointment.

Man, 62 tries is wild but I believe it. My buddy does stand-up in Tulsa and he keeps a notebook where he just writes tally marks next to each joke, one mark per bomb, and he won't cut a bit until it hits like 20. Some of those marks turn into whole new jokes, which is the part that gets me.