Peanut Brittle Woes / Sugar Physics Questions

Joined Dec 19, 2010
I decided to try my hand at peanut brittle today and results have been less than stellar. I'm a bit baffled why.

I started with 1/2C water, 1C sugar over medium heat. My understanding is that hard crack happens at 300-310F, so that was my target temperature. At 275F, the whole thing seized into a powdery mess. Applying further heat gradually turned the powder to a brown, carmel-y substance.

My analysis of what happened: I overshot the target temperature. At some point past 310F, every last bit of water was gone, resulting in the powdery mess. The further heat just melted this remaining sugar into a carmel. Conclusion: I need a new candy thermometer.

I grabbed a different thermometer and started again. At 275F, the exact same thing happened.

Two thermometers being off by an identical amount seems like an incredible coincidence - hence, I'm pretty confused. Is my analysis reasonable? Ideas what I should be doing differently?


Staff member
Joined Oct 7, 2001
It's not a temperature issue.  Your sugar just crystalized.  You may have had some impurities in it (small enough that you couldn't even see it), or in your pan, that sugar crystals started to form around.  Once this happens, no amount of heat will melt it again and applying more heat will just burn it.  This can be avoided by adding a small amount of corn syrup (an invert sugar syrup) or a small amount of acid such as lemon juice or cream of tartar to your sugar as you melt it.  Both will help in avoiding crystalization.  Since I'm not a candy guy though, I don't know if doing that will affect the final outcome of brittle, in term of texture.  You can also help avoid crystalization by washing down the sides of your pan with a pastry brush dipped in water, during the early stages of cooking, and making sure you don't stir the syrup after all the sugar has dissolved.
Joined Dec 19, 2010
Thanks, that makes sense. I'll try to track down a recipe that incorporates corn syrup and/or tartar. If an impurity that small can cause problems, it seems to me the peanuts themselves would be pretty likely to trigger crystalization with a straight sugar/water mix.
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