There are all kinds of ways to thicken soups, including the addition of various grains, a roux or some white sauce, egg yolks, and vegetables.
A common way to thicken soups that also adds to the character of the soup is to add grains or cereals to the soup. Bring the soup to a boil, and in the last hour of cooking, add the following amount of the grain specified for each cup of liquid you have. Immediately reduce the soup to a simmer, and let cook for an hour. These amounts will produce a light thickening effect:
- 1 teaspoon barley
- 1 teaspoon rice
- 1 teaspoon oatmeal
- 2 tablespoons wheat germ flour
- 2 tablespoons peanut flour
- 2 tablespoons soy flour
- 1/2 teaspoon quick-cooking tapioca
You can thicken soups with flour in several ways. One is to make a roux with 1-1/2 teaspoons each of butter and flour for every cup of liquid in the soup. Pour the soup into the roux, bring it to a boil, stirring constantly until smooth. You can also make a paste of 1-1/2 teaspoons of flour for every cup of liquid in the soup. Mix the flour with twice as much cold stock, water, or milk, and pour the paste into the boiling soup, stirring attentively. Let it simmer for 5 to 10 minutes as you stir.
The addition of egg yolks to a soup thickens and also makes it much richer. For each cup of soup, you could add 1 egg yolk beaten with a tablespoon of cream or sherry. It is safest to temper the eggs by adding a little of the hot soup to the egg container, mixing it thoroughly, and then adding that mix to the soup. This will help keep the eggs from curdling (scrambling). You add eggs to a soup right when you are about to serve it, and at all costs, keep the soup from coming to a boil.
You can also grate three tablespoons of raw potato into your soup for every cup of liquid. Simmer the soup for at least 15 minutes after you add the potato.
A common peasant method of thickening soup is to stir in dry, crustless French or Italian bread, and let it simmer for a bit.
You can also make a white sauce and add as much or little to your soup as you like.