This is a great activity to allow students to learn about the additives within their food. Most students don't think twice about what they put into their mouths, and this activities gives students a bit of insight into their favorite foods.
The project usually takes about two weeks (depending on how many times you see your class). It's a great activity that the kids really love doing. At the end, I generally ask them what they learned, and many say that this was a great experience and enjoyed it.