I am looking for a fast and easy marker to follow the grinding of yeast?

I grind baker yeast to perform a certain reaction. Unfortunately, the grinding is not always efficient and I obtain variable results. I have tried to follow it with a microscope but I do not see a significant difference before and after grinding: the same spheres both qualitatively and quantitatively. I am looking for a fast and easy marker to follow the grinding of yeast/ Any idea would be welcomed