Thick soups and thin soups both have their adherents, and both are widely popular. Thick soups are especially comforting during colder parts of the year, or at any time when the weather is inclement. Many thickened soups rely on a "roux" of flour for their thickening, but with celiac disease and wheat allergies becoming more common, it's not always the best option. Fortunately there are other thickeners for soup, ranging from pure starches to vegetables such as okra and melokhia.
Pure Starch Thickeners
Bring your basic soup recipe to a simmer. Stir your cornstarch, arrowroot or other powdered starch thickener into a quarter-cup of cold water, making a thin slurry.
Pour the starch slurry into the soup slowly, stirring or whisking constantly. Continue to stir until the starch has reached its maximum thickening. The time required will vary from one starch to another. Consult the instructions on the packaging.
Repeat, if necessary, until the desired consistency is reached. Taste the soup, and adjust the seasoning if necessary. Remove the soup from the heat and serve immediately, as the texture of the soup may change if it is cooled and reheated.
Thickening with Starchy Ingredients
Dice potatoes, sweet potatoes or other starchy vegetables. Add to your soup pot, and bring the contents to a simmer. Cook until the vegetables are fork tender.
Puree the soup in small batches in your food processor or blender, or use an immersion blender to puree the entire pot of soup.
Return the pot to the stove top, and simmer until it has thickened to the desired degree. If the soup becomes too thick, add water or broth until it reaches the desired consistency. Taste and adjust the seasoning before serving the soup.
Follow the same technique to thicken the soup with bread or rice. Rice is the traditional thickener bisque, and bread is often found as a thickener in older European soups such as ribollita.
Using Vegetable Thickeners
Trim the stems from okra pods, and peel the tough skin at the stem end. Cut crosswise into rings of the desired thickness. If using fresh melokhia, cut off the stems and mince the leaves finely. If using dried melokhia, crush the leaves and water them, so they reconstitute and swell.
Bring your soup or broth to a simmer in a suitable pot. Add the okra, if using, and simmer until the okra is very tender. It will produce a gelatinous thickener as it cooks.
Bring your pot to a full boil, if using fresh or dried melokhia. Fresh melokhia will need to be boiled for 10 to 20 minutes to develop its full thickening power; dried melokhia will need to cook for up to 30 minutes.
Taste the soup and adjust the seasoning, once it has reached the desired consistency. Serve hot.
Melokhia is a green, leafy vegetable native to Egypt. Like okra, it produces a gelatinous thickener when cooked in liquids. It is available primarily from specialty retailers catering to the Middle Eastern market. Melokhia is available in fresh or dried form.