Peanut brittle may seem like the simplest holiday treat, but it requires complicated chemistry to perfect.
Nothing characterizes the holiday season like the snap of a good homemade nut brittle or the stretch of a soft caramel. Like many traditions, this is more about grandparents pulling out their candy thermometers and gathering families into the kitchen than it is about the finished toffee or hard candy. But like any successful experiment in the lab, knowing the purpose of every reagent in these candy-making reactions is the key to ensuring a good outcome.
Peanut brittle relies on sugar in its non-crystalline form, so the first step to making it is to break down the disaccharide sucrose (common table sugar) to separate it into the monosaccharides that make it up—fructose and dextrose—which requires acid, water, and heat. As the sugar dissolves in water, the hydrolysis reaction will continue as long as the sugar and acid are in a fluid state, which depends on the amount of water present and how quickly it evaporates. You can control this by watching the temperature closely. For peanut brittle, start with a quantity of water that is 20-50% of the sugar by weight, and heat the solution over high heat.
As the water converts to steam, the monosaccharides begin to saturate the solution, increasing their tendency to form crystals and precipitate, which results in a gritty brittle. To prevent this, you need to interfere with the ability of fructose to rejoin dextrose. Once the solution reaches a boil, stop stirring it, since this can create cool pockets that promote crystallization. At this stage, it helps to add agents that chemically interfere with crystallization such as other monosaccharide sugars or acids. Acids tend to make syrups more prone to browning and more hygroscopic, making them soft and sticky. For brittles, glucose is the best option. Keeping the sides of the pot clean of crystals by brushing it with water can also help avoid crystallization as these crystals may seed crystallization in the solution.
Cooking is complete when the sugar reaches a certain level of saturation, which can be measured using a refractometer. But luckily for those of us who don’t keep a refractometer at home, sugar cooked to a certain temperature will always contain the same percentage of dissolved solids, so we can simply monitor our reactions using a candy thermometer. For peanut brittle, the proper level of saturation occurs at 110oC, which is where you can quickly stir in the peanuts (or substitute sesame seeds, other nuts, or cocoa nibs). Continue cooking, stirring constantly to roast the nuts and further saturate the sugar solution until the mixture reaches 155oC.
While 155oC is actually below the temperature at which sugar caramelizes, the amino acids present in the nuts contribute significantly to the Maillard reaction—a set of chemical reactions that browns everything from roasted squash to seared ribeye steak—speeding up flavor development.
When ready, remove the brittle mixture from the heat and add butter, vanilla extract, and salt to flavor your candy. Baking soda is also very important at this stage since it reacts to the heat, creating carbon dioxide that aerates the caramel, enabling it to snap when someone bites into it rather than requiring them to gnaw at it until it breaks or pulls apart. Baking soda also raises the pH of the mixture, promoting the Maillard reaction and giving the brittle its particular color and flavor profile.
Finally, pour the mixture onto a marble slab or cookie sheet so that it will cool quickly and evenly. You can stretch it as it cools if desired, or simply break it into pieces and serve it after dinner.
FAQs
Baking soda releases bubbles into our candy (you can see this on a more extreme level in my honeycomb recipe, which uses 5x the amount of baking soda!). This makes the brittle more delicate, crisp, and less chewy, which ultimately makes it more snappy and less likely to obnoxiously stick to your teeth.
Why didn't my peanut brittle get hard? ›
The main reason why peanut brittle doesn't get hard and have the crunch we expect is because the sugar was not cooked long enough. The sugar needs to be cooked to what is called the hard crack stage, 300ºF.
Should you refrigerate peanut brittle? ›
To store: Store peanut brittle (once it's completely cooled) in an airtight container at room temperature. Do not refrigerate as the moisture from the fridge will cause the brittle to soften. Store for 6-8 weeks. To freeze: Peanut brittle can be frozen and stored up to 3 months.
Can you use parchment paper when making peanut brittle? ›
You'll also want to prepare a baking sheet, with either a silicone mat or parchment paper. The mat/paper will help ensure the peanut brittle doesn't stick directly to pan once it has cooled.
How do you fix failed peanut brittle? ›
Why Is My Peanut Brittle Chewy / Sticky / Didn't Harden?
- Break up the brittle and place it in a glass, microwave-safe bowl. Heat on HIGH heat 1-2 minutes until soft and semi-melted. ...
- Transfer the semi-melted brittle to a a clean saucepan. ...
- Immediately remove from the heat and add additional 1/2 teaspoon of baking soda.
If you overcook the brittle, it could be bitter or burnt. If you undercook it, the brittle won't properly set and the end result will be sticky.
How do you keep peanut brittle crispy? ›
To accomplish this, spread a layer of wax paper along the bottom of your airtight container. Then add a layer of brittle, ensuring there is a bit of space between each piece. Next, add a second layer of wax paper and a second layer of brittle. Repeat the process until all your brittle is properly stored.
Why does my peanut brittle have bubbles? ›
As the sugar is cooking and begins turning amber in color it accumulates small amounts of acid, and that acid reacts chemically with the alkaline baking soda releasing about a zillion minuscule bubbles of CO2 that get trapped, making the sugar porous and, well… brittle.
Does weather affect making peanut brittle? ›
I've learned that brittle is better when made on a cool, dry day. When I've made the candy on a warmer, humid day, it tends to be a stickier brittle. This is because the brittle takes longer to cool, and it reaches a point where it is no longer evaporating moisture into the air.
Why does peanut brittle turn out chewy? ›
Once your peanut brittle has fully cooled and set, break it into pieces and store in an airtight container. It's best kept at room temperature in a cool, dry place, away from any moisture. Brittle loves to soak up moisture, making it chewy. If you notice it getting sticky, it's likely exposed to too much humidity.
How Long Does Peanut Brittle Last? Properly stored (in an airtight container at room temperature), peanut brittle will last one to two months.
Why is my peanut brittle cloudy? ›
Pour onto prepared pan and spread to form a single layer of peanuts. Cool completely, then break into pieces. It is important not to stir this mixture after it has dissolved. This will cause the mixture to crystallize and will result in a gritty, cloudy product.
Why put baking soda in peanut brittle? ›
Baking soda is also very important at this stage since it reacts to the heat, creating carbon dioxide that aerates the caramel, enabling it to snap when someone bites into it rather than requiring them to gnaw at it until it breaks or pulls apart.
Why is my peanut brittle not turning brown? ›
If your peanut brittle reached 311°F but is a pale milky color, it's likely the candy cooked too quickly. It reached the correct temperature but didn't cook long enough to undergo sufficient Maillard reactions and develop the characteristic brown color and rich, roasted flavor. Next time, cook at a lower temperature.
How can you tell when peanut brittle is done without a thermometer? ›
If you do NOT have a thermometer, here's what you do. Take a very small cup of cold water and drop a bit of the mixture in. If it dissolves into the water, it's not ready.
What happens if you add too much baking soda to something? ›
Make sure to bake the batter immediately. Baking soda has an indefinite shelf life if stored in a sealed container in a cool dry place. Too much baking soda will result in a soapy taste with a coarse, open crumb.
What causes peanut brittle to be chewy? ›
Why did my peanut brittle turn out chewy? The likely cause is that the sugar mixture didn't reach the proper hard crack stage temperature. Ensuring it reaches 300˚F is key to getting that classic brittle texture.
What happens if you put too much baking soda in peanut butter cookies? ›
Using too much baking soda or baking powder can really mess up a recipe, causing it to rise uncontrollably and taste terrible.
