There is a way to check for expired yeast.  This is how I do it -

Put 1 tsp. in a 1/3 cup of warm water (110 degrees) and add in 1 tsp. of sugar...stir it around
and wait 5 minutes...if it gets bubbly and foamy the yeast is good...if there is no 'action' the yeast is
probably bad and is not good. 

Hope this helps!