For 20 years, I have asked my kids, "Who wants to open up a new bag of yeast?" Invariably someone will. If not, I get all the fun to myself.
The vacuum-packed yeast starts out very hard.
Once the air hits the yeast, it immediately gets soft.
This 21 second video is of my daughter Amy. My husband didn't realize what we were doing so is talking to our dog at the end. I don't know how to edit his voice out. We couldn't do a retake because once the yeast goes soft, there isn't a way to make it hard again unless it would get re-vacuum-packed.
If you're looking for a cheap way to entertain your kids, this is the ticket.