Short Answer: High cooking temperatures and inappropriate cooking materials can cause the sugar mixture to burn or heat too quickly.  Peanut brittle requires low heat for cooking. You may feel tempted to speed up the cooking process by increasing the heat. However, this causes the sugar to brown too quickly and easily burn. You should also keep a close eye on the sugar as it cooks, stirring it constantly with a wooden spoon or heatproof spatula. Using a heavy-bottomed pan also helps to distribute the heat evenly. If you notice the sugar browning too quickly, remove the pan from the heat and continue stirring before returning it to the stovetop.