preservation of mushroom stock

[Calvin Anderson]

Regards all,
  Recently gathered too many shaggy manes (coprinus comatus)to eat
before they would decay so decided to make a mushroom stock (boiled than 
simmered for about an hour, strained, cooled,and froze) to be used for 
soups etc. later.
  The stock is very rich and only takes a very small amount to highly 
flavour a sauce. I've never seen any mention of makeing a mushroom 
stock anyplace, and wonder if this is a safe practise. Seems like a very 
good way to stretch a short lived resource if it is safe. 
  Does anyone have an opinion about how safe this is.
                            Thanks, Cal