Honeycomb Toffee

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Note: this is not an experiment—because you can eat the results. This is a cooking project that shows how science is part of our everyday lives! Take care! The syrup formed in the recipe gets extremely hot. Please make this recipe as a family—with plenty of adult supervision.

Sugar is a very important part of candy. While candy is sweet, it usually doesn’t look or feel like the sugar we use to sweeten coffee or tea.  Heating sugar causes it to change in many ways, including the color and texture.   Careful heating turns sugar into caramel. 

You can make and eat caramel by itself or you can pour it over nuts to make nut brittles.  You can suck on it and it will dissolve in your mouth.  Caramel is hard and brittle.  But, if you add just a bit of baking soda, you can make an entirely different type of candy—still sweet but with a totally different texture. 

Baking soda is a very versatile substance.  It can be used in food, as a medicine and even to clean your counters.  Baking soda is a leavening agent, which means it causes cakes and cookies to rise when they are cooked.  Baking soda is used in the batter along with an acid (such as vinegar, lemon juice or buttermilk).  The baking soda and acid react to form carbon dioxide gas.  The carbon dioxide gas bubbles throughout the batter, created a light an airy texture. 

Honeycomb toffee uses the same principals to make a light and airy candy.  Vinegar is added to the sugar/corn syrup mixture.  The mixture will become very hot when it is heated (be careful!).  Observe carefully when you mix in the baking powder.  Watch how the syrup changes colors and textures as the baking soda is distributed.   

Honeycomb Toffee (Sponge Candy)


  • 1 cup sugar
  • 1 cup corn syrup (light or dark)
  • 1 tablespoon vinegar
  • 1 tablespoon baking soda
  •  9 x 13 inch baking pan

1) Line the baking pan with foil and grease the foil. 
2) Mix the sugar, corn syrup and vinegar in a medium saucepan.  The mixture will bubble, so be sure the pot is large enough to hold everything!
3) Heat the sugar mixture over medium heat, stirring until the sugar melts. 
4) Once the sugar melts and the mixture starts to bubble stop stirring.  Cook until the mixture measures 290oF (hard crack) on a candy thermometer.   The solution will be extremely hot!
5) Turn off the heat and mix in the baking soda.  The mixture will lighten in color and become opaque.  Do not over mix because too much mixing will deflate the bubbles.
6) Pour the mixture into the pan.  Allow to cool.  Break into pieces and enjoy!