Help - Wormery liquid fertiliser

Two questions please.  The latest three pints or so from my liquid fertilizer from my wormery is light in colour, almost the same as tea - and smells quite acidic.  It almost fizzes when I add water.  Why has my wormery produced this in contrast to the lovely brown liquid it has provided for years.

And, I've been told that liquid fertilizer from wormeries doesn't keep very long because its full of bacteria.  I have some from last year, is it useless now?