Friday, August 26, 2011

Crystal structures and catching CO2 with Sponge Candy

I really love science, and I love cooking, so it seems natural that I keep teaching Little BBQ lots of science in the kitchen. This time I took my Daring Bakers challenge which was candy this month and turned it into a science experiment for Little BBQ. Sponge candy is a very simple candy to make with lots of interesting science.
Basically sugar is heated to a high temperature where it turns into the “soft ball stage” then baking soda (Sodium bicarbonate [NaHCO3]) is quickly added to the hot sugar. The heat from the hot sugar causes the baking soda to release carbon dioxide bubbles. Then, the candy is quickly cooled and the carbon dioxide bubbles get trapped in the candy and the sugar does not have time to line up into ordered crystal structures. Another trick to sponge candy is that you add an interfering agent that contains high levels of fructose like corn syrup or honey. The interfering agent helps to prevent the sugar from lining up and making hard crystal structures that gives some candy a grainy texture.  Instead the sugar will look glassy and disorganized under a microscope.
For our little experiment we took microscope pictures of sugar as our control. Then, we made the sponge candy. We made sure that we had holes in our candy. Then, we placed the sponge candy back under the microscope to see if the sugar had enough time to make organized structures. It appears that we made our sponge candy properly because we found air pockets from the CO2 and glossy, disorganized sugar structures.
Little BBQ got so into this experiment and the science behind it that he wanted to know more, so I drew a picture of sugar at the molecular level. I let him color all the carbon, oxygen, and hydrogen atoms different colors, and we counted how many bonds each atom has connected to it to make general rules about hydrogen bonds, carbon bonds, and oxygen bonds. I am very proud of Little BBQ on this experiment. For the sponge candy recipe, please see my cooking blog post on sponge candy.

More microscope images of sponge candy:


  1. The Carnival of homeschooling is up, and this post is in it. Please help us all out by spreading the word.=)

  2. what a neat experiment! Thanks for stopping by, glad you found my post on co-ops useful :D

  3. Fascinating! What a great Science teacher you are! Does sponge candy taste good? How old is Little BBQ?

    I might try this. How do you take microscope pictures?

  4. Penney, Little BBQ is 4.5 years old, so the candy is appropriate for a young child if you are careful with the hot sugar. The sponge candy does taste good, but it is very sweet. For the microscope pictures we use Bresser Junior Digital Hand Microscope. The microscope does not require you to look through an eye piece to adjust the focus because the image comes up directly on your computer screen, so it is very easy for little hands to adjust. We got the microscope at Toys R Us. The product got bad reviews on-line, but we have been very happy with the product for our use. We also had no software problems on our PC. I think some Mac users have had trouble.

  5. What a cool experiment! Thank you for the recipes and the ideas. My children love science, even though I don't, and I think it's because I throw open the doors of the kitchen to them so they can explore and learn. I think I know what I'm doing for science this year...

  6. wow this is real retty cool. i am thinking abou using this for my school project. hmm...i wonder how much candy a bunch of pre-lunch teenagers will eat....thank so much for the idea :D


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