I use protein sparingly, and it seems to last forever, at least in a tub. Probably depends what sort of environment it's been kept in. I agree with Ryano's caution, but your nose should be a reasonable indicator. You could always try an itsy-bit, and, if you survive the experience, try a bit more.
230 strict press @ 220; bodyweight+187 X 4 dips @ 180; 403 front squat @ 210; 10 000 push-ups.
Ignoring irrelevant credentials since I was 17.