Pyrolysis has many applications in food preparation.
Caramelization is the pyrolysis of sugars in food (often after the sugars have been produced by the breakdown of polysaccharides). The food goes brown and changes flavor. The distinctive flavors are used in many dishes; for instance, caramelized onion is used in French onion soup. The temperatures needed for caramelization lie above the boiling point of water. Frying oil can easily rise above the boiling point. Putting a lid on the frying pan keeps the water in, and some of it re-condenses, keeping the temperature too cool to brown for longer time.
Reaction of Caramelization : 
Pyrolysis of food can also be undesirable, as in the charring of burnt food (at temperatures too low for the oxidative combustion of carbon to produce flames and burn the food to ash).