How you know if a person has experienced fermentation? explain

You have probably experienced fermentation yourself when you've had to run the extra mile really fast just so you will not be late to class. You know that burning or stinging sensation that you feel in your muscles when you push yourself running?  That's caused by a buildup of lactic acid in your muscles. No matter how hard your lungs and heart work to get oxygen to the cells in your leg muscles, they still aren't getting enough to produce all the energy they need through cellular respiration.  So, they are forced to switch to fermentation, and lactic acid is produced.

The answer is joseph is observing the colour of the reaction mixture to see whether proteins are present in the given solution.