Why Apple Juice?
Apple juice contains naturally occurring sugars, which makes it a common starting material for fermentation experiments.
That’s why a setup involving sweet juice + a balloon over the bottle immediately raises the possibility that someone is experimenting with fermentation.
However, the photo alone cannot tell us exactly what was inside the bottle or what your niece intended to do with it.
It could potentially be a science experiment, a fermentation project, or simply an unusual homemade setup.
