Agre dulce is a type of vinegar that tastes sweet. Vinegar is usually sour and comes from things like fruit or grains that are fermented, or allowed to sit and break down. Agre dulce is made by taking vinegar and adding sugar to it, which makes it taste sweet instead of sour. Think of it like putting sugar on something normally sour, like a lemon. Agre dulce is used in cooking to add a sweet and tangy flavor to dishes, like in salad dressings or marinades for meat.