<human>:  Why do you need to add the sugar to a recipe for braising vegetables?
<bot>: Sugar is added to the recipe to help the vegetables caramelize. Caramelization is a chemical reaction that occurs when sugar is heated. When sugar is heated, it breaks down into smaller molecules, which then combine with other molecules to form new compounds. These compounds are called caramel. Caramelization is a key step in the cooking process, as it helps to create a rich, flavorful dish.