Fermentation needs sugar as fuel. Yeast turns that sugar into gas and alcohol. Juices with more sugar produce more fermentation, which is why orange juice fermented the most in this test.

Yeast is a tiny living thing that eats sugar and makes gas. You add one gram of yeast to containers of orange, apple, and cranberry-grape juice. The juice with more sugar produces more gas.

Sugar content varies across fruit juices, and a Brix meter lets you measure exactly how much is present before and after fermentation. You pour 250 milliliters each of orange, apple, and cranberry-grape juice into separate containers, then measure the Brix reading of each. After adding one gram of yeast and waiting 72 hours, you measure again. The drop in the Brix reading shows how much sugar the yeast consumed.