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.
I just tested 50g/50g/1g (water/flour/yeast) stirred in a small glass bowl with my old (18month) batch of Fleishmanns ADY and my new batch. They are both stored in the freezer in a glass jar. Surprisingly the OLD batch rose slightly faster than the new batch. Both would more than double in about an hour at that ratio. My compressed yeast (OLD and NEW batch), also stored in the freezer, was a different story. This batch is over a year old and was stored in the fridge for 2 weeks before putting the 20# of blocks into the freezer. This new batch, I stuck in freezer right away. Hopefully it will fair better. The old batch was getting pretty weak. I'd guess 1/3 strength at 1 year old. Compressed yeast is crumbly when new and kind of squeaky, and light tan in color. After freezing a year, it turns more gel like and sticky and is more of a medium tan with almost a burnt orange color. It still works (just not as well). It still smells the same and probably tastes the same in the recipe.