I make bread about 2-3 times a week (all the bread we eat) and get yeast in a small jar (Fleischmann's), kept refrigerated. For a mid sized bread, I use 5/8 teaspoon of yeast. However, I have noticed that, the older the yeast, the less the dough rises. When the yeast is pretty old, the dough is as much as an inch below where it rises when it's new, in a KitcheAid mixer metal bowl (about 1 gal). As a result, the bread is thicker and less fluffy.
Does yeast lose strength over time and should I add a little more yeast as it ages?