I contacted a Makerjuice chemist and asked what happens chemically when resin goes bad but all he said was "Typically what you will see is the viscosity slowly increase and/or the resin will become less reactive when it reaches the end of its shelf-life. We normally give our products a 1-year shelf-life, but that's not to say that it could be perfectly fine after 1 year." So I still know nothing about what actually is happening.