Papain (natural Papaya-based enzymatic meat tenderizer) does not have a fixed expiration date where it suddenly flips to zero activity. Its tenderizing strength declines on a curve, and storage conditions matter.
- Sealed, cool, dry storage: best - can likely hold meaningful activity 1-2+ years.
- Exposed to heat, humidity, or light: activity drops much faster - it could be significantly weaker in months.
- Package opened and repeatedly exposed to air or moisture: faster decline than an unopened jar.
If your papain is older, but still smells like papain, and has been stored reasonably cool and dry, it will likely still tenderize, just possibly less aggressively than when fresh. If you want to be sure it is still active, a simple test is to sprinkle a bit on a small piece of raw meat and check for surface softening or breakdown after 15-20 minutes. That tells you directly rather than guessing from age alone.