Comfrey Liquid

I made some comfrey liquid last year or maybe the year before and was wondering if it is okay to use it this year, does anyone know how long it lasts ???

I make a large batch every couple of years and store it in 2 litre plastic bottles.  As far as I can tell, it's just as good when a couple of years old than when 'fresh' (in quotes as it's strange word to use for such a smelly liquid!)  My toms are going great guns on 2 year old stuff at the moment.  You could always do a test on something fast-growing, like lettuce - plant two in identical pots and only feed one with your comfrey brew and compare how they grow.

Thank you so much Bob, will give it a go.