Two things I love: chocolate and science. This video shows you how to make chocolate pop rocks. Pop rocks was a crazy new candy when I was a kid. Put them in your mouth and let the crackling begin. Pop rocks is basically a mixture made when sugar and water are heated and then injected with carbon dioxide gas. The cooled mixture is the pop rocks. Put them into your mouth, the sugar disolves and the carbon dioxide gas gets released (the pop). Chocolate is a complex mixture of many ingredients, primarily sugar, cocoa butter, cocoa liquor, milk or milk powder (for milk chocolate), and vanilla. Chocolate can be melted and mixed in with other ingredients to make many different flavor combinations. Basically this demo shows how to properly melt (temper) milk chocolate and mix in flavorless pop rocks (called pastry rocks). The results are delicious pieces of chocolate that melt in your mouth which lead to a suprise crackling of the pastry rocks. Science topics that are covered include energy in phase changes, properties of mixtures, and crystalization (chocolate has to reach specific temperatures in the melting process so that cocoa butter crystals form evenly).
I recently started a food science club at school with a fellow teacher. It's a good way for me to try out new stuff with a small group of students, that I eventually want to incorporate into my classes. It's like a real life R and D department. I recently posted about a polymer called sodium alginate. I got a response from Earl Lee on how to make watermelon caviar. So I decided, let's try it out with an after school club. It demonstrates a technique used in molecular gastronomy. A polymer (which is in one of our standards), sodium alginate, is mixed in with watermelon juice. The mixture is then carefully inserted, with a syringe, into a solution of calcium chloride. A chemical reaction happens between the calcium chloride and sodium alginate to form calcium alginate. The calcium alginate is not soluble in water and thus forms a gel around the outside of the watermelon juice. The calcium alginate watermelon spheres are edible. We then experimented with making spheres of cola using the same technique. The students loved the more intense (not to mention the more sweet flavor which their palettes are more geared to) flavor of the cola.
This is another favorite demo of mine. Throughout the years I had mixed results. I finally figured out that Gold Medal all purpose flour works the best with some preparation. I sift a small bag of flour to reduce clumping and ensure the separation of particles. When doing this demo be aware of what kind of fire alarms/detectors are used in the building. In my classroom there is no sensor that will go off. Where I recorded the video, our school's multipurpose room, it (it was about 30 feet above the demo area) could detect the heat/smoke that was released (the alarm sounded about 1 minute after the actual demo).
A polymer, sodium alginate, reacts with calcium chloride to produce calcium alginate. Calcium alginate is a gel that is not soluble in water. A new branch of cooking, called molecular gastronomy, uses this technique to trap flavor sauces in gels to put over food. Not familiar with molecular gastronomy? Lifehacker has a good set of simple videos on the subject. You can order the kit that I used from Educational Innovations.
System A and System B monomers are mixed and polyurethane foam, a polymer, is produced. You can see the dramatic results in a clear cup, or a little more weird, in a latex glove.