I think I might want to open it first and make sure it hasn't skinned over.
Maybe shake it a little by hand first and make sure you can hear it
moving around first. If it's still liquid and not gelled or skinned over
it should be fine.
You'll know when you strain it.
In the future consider pouring off into 1 quart cans before storing.
A gallon can half full is a lot of air in there.