It may be too late for you, but one that my daughter did recently is to examine "how does the quantity of salt affect how much a loaf of bread rises?" She precisely measured out ingredients (to the tenth of a gram in some cases) ingredients for four loafs of bread, keeping all of the ingredients precisely the same except the amount of salt, which she varied from none to normal to twice to four times.
Her teacher said it would have no effect and initially rejected her idea. The teacher was very, very wrong!
Food science has a lot of interesting and pretty basic experiments.