Fudge Factor

    Kids, what is it about the texture (the “mouth feel”) of fudge that just makes it taste so good?  Did you know that this texture can be defined by crystals?  Little teensy sugar crystals that are completely surrounded by a very concentrated sugar syrup.  So, in making your own fudge, you are actually doing your own science experiment in making crystals.

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

    As a demonstration, you’ll need a heavy-duty 2-quart saucepan, a wooden spoon, 2 cups sugar and 2 cups H2O.  Combine and have an adult partner bring to a boil on a stove.  You’re also going to need a really good thermometer (best is a digital candy thermometer).  When all of the sugar crystals dissolve, a syrup is created.  On a molecular level, the solution's not too hot, so they're moving around slowly and the molecules are more attracted to the surrounding water than they are each other.  Put on the lid for three minutes.  The trapped steam will condense on the lid, roll down the sides, and dissolve any sugar crystals that might be stuck there, waiting to set off a chain reaction of crystallization.  Take off the lid and put in the thermometer.  As the solution boils it becomes more concentrated because the water can escape as steam but the sugar can't.  As a result, the temperature of the solution begins to rise beyond 212 oF.  So not only are the sugar molecules moving around a lot faster now, they don't have near as much room to move in.  In other words, this solution is concentrating.  Now, by watching the temperature, you can gauge when the concentration is right for forming the crystals.  This controls the candy of your choice.

    An adult partner can try this with a wooden spoon.  When a small dollop of syrup is dropped into cold water, it behaves in a very specific way that depends on the sugar concentration.  From 230-234 oF, it forms soft threads.   Between 234-240 oF, it forms a soft ball, which is just right for fudge or pralines.    Between 244-250 oF, you get a firm ball, good for caramels.  From 250-266 oF, you get a hard ball (great for nougat).  Taffy makers wait for 270-290 oF when hard but pliable threads form in the water.  Threads also form between 300-310 oF, but these are very brittle but perfect for hard candies, brittles and lollipops.  The website version of this article shows pictures of all these stages.  Let the syrup cool completely and dispose.  The reference below has a true fudge recipe; the trick is to keep the crystals small enough by proper temperature and vigorous stirring.  Big crystals make grainy fudge.  Yuk.

    Can you make decent fudge in a microwave?  No.  But you can make a nice fudge-like candy and it’s a whole lot safer.  Cut up 2 sticks of unsalted butter and add a cup of peanut butter in a microwave-safe bowl.  Stir till smooth.  Cover with plastic wrap, poke a couple of holes for steam, and microwave on high for 2 minutes.  Since we're not making a syrup, the large amount of fat here will make a liquid thick enough for the crystals to suspend in.  Carefully remove the plastic wrap just enough to get a wooden spoon in.  Give it a good stir, re-cover, and microwave for another 2 minutes of cooking on high.  It’s really hot now so use oven mitts.  Add 1 tsp vanilla and 16 oz powdered sugar.  Stir until the luster is gone (it gets so thick that a potato masher works best).  Scoop into a well-greased 8” x 8” glass baking dish and put in the refrigerator. 


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    May 2006



    Alton Brown of TV Food Network’s “Good Eats” at