Opening the lid of your slow cooker to sneak a peek at the meal being cooked inside is a mistake because the airtight lid helps maintain a consistent temperature inside the cooker.

Per the Extension at the University of Minnesota, the heat built up inside the cooker escapes each time you open the lid, dropping the internal temperature by 10 to 15 degrees F.

The university says each peek could add about 30 minutes to your cooking time. Plus, it could leave the meal undercooked and cause food poisoning if you’re cooking meat or poultry.

However, if you want to thicken the cooker’s contents, removing the lid for 30-45 minutes and setting the heat to high can be helpful, as it lets the steam and excess water escape.