A thick bowl of clam chowder may be just the thing for a cool evening. But even then, you don't want a soup so thick it will hold up your spoon. You might be tempted to just add a bit of water when you need to thin the soup. That simple solution works for some soups, but it may thin the taste as well as the texture. When thinning soup, err on the side of adding too little liquid rather than too much. You can always go back and add small amounts of liquids incrementally. Since most soups provide a nourishing meal, it makes sense to choose thinning agents that help to maintain a high level of healthfulness and flavor.
Add Some Water
If your soup is a hearty mix with lots of strong flavor, 1/4 cup of water is just the thing for thinning, adding neither fats nor calories. For example, a bit of water won't drown out the taste in a sausage gumbo with a dark roux or in a spicy soup based on classic chile con carne. On the other hand, water will thin the balance of ingredients in a delicate fish consomme.
Acidity to Brighten and Thin
A little vinegar, lemon juice or lime juice add a brightness to soups as well as thinning them to a small extent (not to mention adding a small dose of vitamin C). Use about 1 tablespoon for a pot of soup to serve three or four people. Lime works especially well in Thai or Korean-inspired soups, while lemon juice complements mild-flavored cauliflower soup or stronger tasting carrot or sweet potato soup. Try rice wine vinegar for chili soup and red wine vinegar, sherry vinegar or balsamic vinegar for mushroom soup or lentil soup.
If you need to thin even more, go with about a 1/4 cup of white wine for vegetable or fish soups, red wine for beef-based soups and sherry for mushroom soup. Cook the soup for about 5 minutes after adding wine to remove any alcohol while retaining the deep wine flavor.
Stocks and Broths
For the most healthy choice to thin soup, choose low-sodium beef, chicken, fish or vegetable stock (an unseasoned blend simmered for a long time) or broth (typically seasoned and cooked for a short period). Add either liquid to meat, vegetable-based or fish soups in whatever quantities you need. Begin with a few tablespoons of the liquid or up to 1/4 cup until your soup gets the consistency you want. Boost the nutrition and flavor of the soup by first simmering store-bought stock or broth with a chopped onion, celery and carrot for 30 minutes to an hour.
Milk and Milk Alternatives
Reaching into your fridge for dairy milk, cream, soy milk, almond milk or any other kind of milk gives you a ready-made thinning liquid for pureed soups and soups with a dairy or creamy base. Begin with a few tablespoons of milk and add up to 1/4 cup. Milk of any sort adds extra nutrition to soup, but add it carefully so as not to curdle the soup. Remove the soup from the burner when adding milk, then reheat it on low. Or, warm the milk by adding a little of the hot soup to it before pouring it into the pot. The more fat the milk contains, the less likely it is to curdle when you add it to the soup.