When making a recipe for a soup or stew, you will often run across the same first step: “Sweat the vegetables.” But what does that even mean and why should we do it?Sweating vegetables means to cook them slowly over low heat in a little bit of oil. The vegetables will slowly release some of their natural juices. The goal is to soften the vegetables without browning them. The vegetables end up cooking in a bit of their own liquid. This technique differs from the similar “sauté,” which uses a higher heat and shorter cooking time, and allows the vegetables to brown. Browning the vegetables affects the color and flavor of the final dish, which is not always desired. To really draw out the moisture, add a good pinch of salt to your vegetables. Also, cover the pan as it cooks to trap in steam. Make sure to stir them often so the vegetables don’t have too much contact with the bottom of the pan.
Sweating vegetables is the first step in building layers of flavor in many dishes. It is crucial in soups, sauces, braised dishes and stews. Cooking the vegetables in this way draws out excess moisture, concentrating the flavors. It also allows those initial key aromatics to slowly develop their sugars. As they cook, the flavors marry as they begin to get to know each other in the pot. Sweating is a simple step that only adds a few minutes of cook time and yields far better results than if the vegetables were added raw with all of the other ingredients.
Many vegetables benefit from this cooking kick-start. Onion, carrot and celery – a classic French combination called mirepoix – are the most common vegetables used for sweating. (Mirepoix is 2 parts onion, 1 part carrot and 1 part celery.) But don’t overlook other highly aromatic vegetables such as shallots, leeks, peppers, fennel, garlic, ginger, and even lemongrass.