I make bread and pizza bases using "fast action" dried yeast (like this: http://www.sainsburys.co.uk/groceries/index.jsp?bmUID=1287396076254 ).
My bread recipe calls for one sachet, my pizza dough recipe for two sachets. I notice that when I have just purchased a packet that still has a few months to go on its "best before" date, I get really lovely fluffy bread and pizza. As the yeast approaches its "best before" date, it gets less and less effective, but simply adding more of it doesn't give the same results - should I change the recipe in some other way? For example, add more sugar, or less salt?
I saw this similar question: http://cooking.stackexchange.com/questions/2532/does-active-dry-yeast-really-expire but it doesn't quite answer my query.