As some of you know, I've been making bread a long time, about forty years now. I've used those little cakes of yeast (rarer now--very common when I started, to find them in the refrigerated shelves in stores), active dry yeast, "Rapid-Rise" dry yeast, active dry yeast in little brown jars, bulk dry yeast in sealed 1 pound plastic bags, (bought years back from some place in Austin I've now forgotten--it was where I bought flour in bulk.) I've made bread abroad, using locally available yeast and flour. With all of those I had no trouble producing good loaves.
Awhile back, I bought what was supposed to be dry yeast with indefinite shelf storage until opened, a one-pound package. It was in a heavy foiled-paper packet. The first batch of bread--the same brown bread recipe I've used for years, with flour that had worked perfectly in the previous batch (with packeted active dry yeast) did not do well. There's always an adjustment period from one kind of yeast to another (especially the shift from cake yeast to dry yeast) but I didn't expect a problem with this yeast. And yet...it's acting a bit like "weak" yeast. Although it bubbles up in the initial mix, and feels normal during kneading, the "lift" doesn't keep going. The first rising of dough goes soft before it's as big as usual. Second rising can look normal, but does not even hold in the oven, let along give that final "puff" that a good dough gives. The top of the loaf "crumples" before the bread is baked. I've made three batches with it now, and all have behaved the same way. Flavor is fine, texture--though denser than usual--is even, indicating that the yeast is acting evenly throughout the dough, just insufficiently.
My next step will be increasing the amount of yeast in a batch to see if that's the problem--it's just not as "strong". But too much yeast in a recipe (if it's normal yeast) creates other problems. However, I'd be interested in others' ideas on what might be wrong, and what might be the best way to handle it. And, if you know a brand of bulk yeast that holds its oomph for long shelf-storage before opening, I'd love to know it.