Food Wraps

    Kids, did you ever wonder what the difference is between all those long, rectangular boxes of foils and wraps in your kitchen? This month we are going to have fun by making something tasty and then testing how best to keep it that way.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    First, bake a batch of cookies with an adult partner. Make your favorite kind, especially considering that the holidays are just around the corner. Bake a third of them on a plain, ungreased cookie sheet, a third on a greased sheet, and the last third on a sheet that is lined with kitchen parchment paper. What do you notice when removing your cookies? Greasing a sheet or pan will make the surface slippery so that food won't stick (like one third of your batches probably did). Parchment acts the same way but has the added benefit of making cleanup easier. Why didn't the cookies stick to this paper? Why didn't the paper burn? This parchment paper is coated with silicone molecules, which makes it more slippery and heat-resistant than regular paper. Silicone molecules are polymers of -Si-O- groups (actually, -Si(R2)O- groups).

    Now place half of the cookies on wax paper to cool, and the other half on paper (from brown paper bags or paper plates). When they are cool, what do you notice? Has the wax melted a bit? Wax paper is a thin sheet of paper that is coated with paraffin wax. Paraffin wax is a white wax made up of straight-chain hydrocarbons that contain 26-30 carbon atoms per molecule. And how about the paper that was used to cool the cookies? Are there greasy spots? Such spots are from the melted fat molecules (oil, butter) in the cookie recipe.

    Last, store your cookies individually in different types of wraps and containers. Seal them in plastic wrap, ziploc bags, aluminum foil, wax paper, Tupperware, and paper lunch bags, for example. Every day for a few days in a row (or for as long as they last), test your cookies for freshness. Which method or methods work best? Why? Some materials make better barriers than others against water molecules (which can make things soggy) and air molecules (especially oxygen, O2), which can make cookies stale. Think about how tight the bonding has to be between aluminum atoms, for example, to not let the tiny oxygen and water molecules pass through. Chemists use scientific words like "permeation", "diffusion", and "percolation" when quantifying such properties.


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    December 2003