The optimal duration to keep an electric slow cooker on varies depending on the recipe and the specific slow cooker model. Generally, for most recipes, it is recommended to cook on low for 6 to 8 hours or on high for 3 to 4 hours. However, this can vary. For example, a stew or soup may require longer cooking times on low, while a casserole or rice dish might cook effectively on high. It's important to follow the specific recipe guidelines and consider the type of food being prepared. Overcooking can lead to a loss of texture and flavor, while undercooking can result in an unappetizing dish.

The reason for these guidelines lies in the slow cooker's design and cooking principles. Electric slow cookers use low, consistent heat to gradually cook food, which allows for the flavors to meld together over time. The cooking time is longer than traditional cooking methods because the slow cooker maintains a steady temperature, which is ideal for certain types of dishes. For instance, meats need to be cooked at a lower temperature to ensure they are tender and not overcooked. According to the National Center for Home Food Preservation, slow cooking is a safe method for tenderizing meats and ensuring that they are fully cooked without the risk of foodborne illness.

In summary, the recommended cooking times for an electric slow cooker are typically 6 to 8 hours on low or 3 to 4 hours on high, but these should be adjusted based on the specific recipe and food type. Overcooking can lead to texture and flavor issues, while undercooking can pose health risks. It's crucial to follow recipe guidelines and understand the slow cooker's cooking principles to achieve the best results.