How much should yeast rise?

Question

At some point in the past, I had purhased a large amount (maybe a pound) of instant yeast at a restaurant supply store. I transfered it to a glass container, and have been keeping it in the fridge. I don't remember when I bought it -- I suspect it was 2 years ago. (I know it was more than a year old).

When I make bread, it's still rising, and if I try proofing it, it works ... but the time to get bread to double in volume is taking longer (sometimes up to twice as long) as many recipes give as estimates.

Is there some good test that I can use to estimate what the decreased activity is, so I can adjust the amount of yeast that I'm using? Or is there some other technique that I can use to compensate (eg, start proofing the yeast with sugar before using?)

Answer 1

Sadly, there isn't really a better answer than "enough". You can of course proof the yeast in warm water with a bit of flour to make sure that it's still active (by looking for foam after a few minutes). As far as home testing goes, it doesn't get much more specific.

Even yeast manufacturers doing far more advanced testing of their yeast admit that testing gas produced in a laboratory is a poor predictor of proof times. There are so many other factors going on in yeast doughs that yeast activity alone is a drop in the bucket of protein levels, enzyme activity, amylase levels, falling numbers, farinograph and a host of other test scores that can effect dough.

As far as a technique for compensating, the best method is just to rely on proofing to the size required and allow more time as needed. If you know that your batch of yeast tends to perform slowly you can either work with it warmer or add a bit more yeast to start. If you start proofing with sugar, you're just allowing the yeast some time to reproduce so the effect is pretty much the same as just adding a bit more yeast than called for to your dough.

And, of course, it's also important to make sure that you're handling the yeast appropriately for it's type. Instant yeast doesn't require hydration prior to use, but active dry yeast needs to be added to the liquids in your recipe before the dry ingredients are combined.