Good soup is easier when you understand the decisions behind the recipe. Use this guide as a practical reference, then adapt the ideas to the ingredients and equipment in your kitchen.
Reduce the liquid
An uncovered simmer evaporates water and concentrates flavour. This method is best when the ingredients are already tender and the soup is only slightly thin. Stir more often as the soup thickens so solids do not catch on the bottom.
Blend part of the soup
Remove one or two cups, blend until smooth, and stir it back in. This works especially well with beans, potatoes, squash, lentils, corn, and cauliflower. It adds body without changing the ingredient list.
Use a roux
Cook equal parts butter and flour for about one minute, then whisk in liquid gradually. A roux gives dairy soups and chowders a stable, velvety texture. For best results, avoid dumping dry flour directly into hot soup because it forms lumps.
Make a starch slurry
Mix cornstarch, arrowroot, or potato starch with cold water before adding it to simmering soup. Start small. Cornstarch produces a glossy texture and thickens quickly; arrowroot is useful for some gluten-free soups but should not be boiled for long.
Add a starchy ingredient
Rice, barley, pasta, potatoes, and lentils absorb liquid and release starch. They can turn a broth into a full meal, but they also keep thickening leftovers. Store cooked pasta or rice separately when possible.
Use dairy carefully
Cream, evaporated milk, sour cream, and yogurt add richness more than true thickening. Add them over low heat and avoid hard boiling. Temper yogurt or sour cream with a little hot broth before stirring it into the pot.
Finish with a purée or paste
Tomato paste, bean purée, mashed potato, nut butter, or coconut milk can thicken while adding flavour. Match the thickener to the soup rather than using a method that fights the recipe.