How to collect CO2 from alcohol fermentation?

This is my high school experiment that i'm doing now, determining the optimum temperature for yeast to ferment. I added 11.5 g of yeast into a 1L water (about room temp.) , and then stir it well. After that i added 1.3g of ammonium dihydrogen phosphate into the solution. i left it in a foam box containing water with my desire temp. overnight ( i did it for 20, 40 , 60 and 80 degrees celcius) But i couldnt collect any CO2. Tell my why please. Your answer will me appreciated.