I've been using compressed yeast which has been stored in the freezer for a year now. It rose bread very similarly frozen to how it did when it was fresh. But a year in and it seems like maybe bread is not rising as high. So the question here...
How do I tell when yeast has lost viability? Is there a simple test without making bread with a new batch vs the old?
If it's lost potency, can I just use more yeast?
I've been baking with sourdough a long time but I consider myself somewhat of a rookie when it comes to yeast breads.
Haha 2 posts. Anyway - if it helps ya - 5+yrs and I finally used it all. Can you use more - yes - but I wouldn't - unless it's really dead. Enjoy!
You can tell if it's still viable via proofing. Add yeast to some of the recipe's water (between room temp and 110F/43C) and a little sugar, wait 5-10 min. If it's foamy/bubbly it's good. You can search online for reference photos to see how it should look.
With IDY, going from using a ~7 year old bag stored in the fridge to a new bag of the same brand, I did have to decrease the amount used. So in my experience if the yeast is viable but not very strong, you can increase the amount.
I have no way of knowing how old my yeast (ADY) is but I just experimented on a few loaves and found that if I used the normal amount (x1) it rose much too slowly (took probably x5 as long to rise), and if I used x2 the amount or x3 it rose better and better, so lately I've been quadrupling what the recipe calls for and it's a fast rise but not too fast, still successful I'd say. If you're still insecure after doing the test VerdigRegis kindly shared, you can always make a mini-batch of dough and just watch how fast it rises. Compare that to what your recipe says; if the recipe says it should take 2 hours to double, and instead it takes 4, double the amount of yeast and assume your yeast has lost half its strength.