I have a container of sodium metabisulphite for sterilizing my fermenter and bottles that has gone hard. It is about 1 year old.
Can I still use this effectively or should I use another container that is still soft that I bought last week?
If it's gone hard, it just means that it's picked up moisture from the air. If you can break off the required amount and it dissolves in water, then it will still be effective.