Flour and cornstarch may not be the best thickeners (especially for soups and sauces). There are other options out there that you might consider.

In general, a thickening agent, when added to an aqueous mixture, increases viscosity without substantially modifying its other properties, such as taste. They provide body, increase stability, and improve suspension of added ingredients.

Examples of common thickening agents besides wheat flour and cornstarch include: rice flour, potato flour or flakes, arrowroot, tapioca starch, agar, pectin, gelatin.

All-purpose flour is the most typically used food thickener, followed by cornstarch and arrowroot or tapioca. So what’s the difference?

ALL-PURPOSE FLOUR is typically used for thickening gravies, gumbos, and stews. It must be cooked thoroughly to avoid the taste of uncooked flour. Roux, a mixture of flour and fat (usually butter) cooked into a paste, is used for gravies, sauces and stews.

But note: cornstarch and arrowroot thicken more efficiently than flour since they contain no protein. They have 50 to 100% more thickening power than flour, thus, less of them is needed. They also thicken at a somewhat lower temperature and do not need to be precooked, like roux. However, they do need to be dissolved in fluid first.

CORNSTARCH is actually a flour. It is the endosperm of corn kernels that has been dried and ground. It’s used to thicken soups, sauces, gravies and custard. It’s often preferred over flour because it forms a translucent mixture, rather than an opaque one.

When using, first mix it with cold liquid until it forms a smooth paste, and then add it to whatever you’re thickening. If added directly into the cooking food, it’ll form lumps that are difficult to mash out for a smooth mixture. An easy way to get a lump-free mixture is to put the cornstarch and liquid into a jar with a screw on lid and vigorously shake the sealed jar until lumps disappear. This also works with a flour/water mixture and also makes it easier to slowly add it to a soup, sauce, or gravy.

RICE FLOUR is made from finely milled rice. It’s a particularly good substitute for wheat flour and for recipes that need refrigeration or freezing since it inhibits liquid separation.

POTATO STARCH isn’t a flour. It’s dehydrated potatoes ground into powder and is heavy and dense. It has no gluten. Like cornstarch, it needs dissolving in a little water before adding it as a thickener. And like cornstarch, it’s especially preferred over flour for thickening because it helps recipe remain translucent.

Used to thicken soups and gravies, it should never be boiled. Its main advantage over other starch thickeners is that it's a permitted ingredient for Passover, unlike cornstarch and other grain-based foods.

ARROWROOT, like other starches, is almost pure carbohydrate (no protein), thus it lacks wheat flour’s nutrition. It thickens at a lower temperature than flour or cornstarch, isn’t weakened by acidic ingredients, has a more neutral taste, and freezes well. Its drawback: it doesn't mix well with dairy, (it gets slimy). For acidic foods, it’s a better choice than cornstarch, which loses thickening potency in acidic mixtures.

Arrowroot should be mixed with a cool liquid before adding to anything hot. Heat your mixture only until it thickens, then remove from heat immediately (to prevent the mixture from thinning). Overheating breaks down its thickening property. To use, substitute two teaspoons of arrowroot for one tablespoon of cornstarch, or one teaspoon of arrowroot for one tablespoon of wheat flour.

TAPIOCA is a starch extracted from the cassava plant. It reheats and freezes well. As a thickening agent, it easily completely dissolves and goes clear. The only drawback about tapioca is that it breaks down a little quicker than corn starch, especially when using a very high temperature.

Then there are the vegetable gums:

AGAR (or agar agar), found in the cell walls of red algae, is not a substitute for gelatin. It sets very quickly at room temperature. Historically used as a substrate to contain culture medium for microbiological work, it has now been found to be a healthy and superior thickener for simple recipes (jellies and desserts).

PECTIN is a super thickener and is obtained from citrus fruit peel, apple peel etc. In human digestion, pectin goes through the small intestine more or less intact because it’s less a soluble dietary fiber. Used to make a gel, it doesn’t add any flavor to dishes and is commonly used in making jams and jellies.

And don’t forget this protein thickener:

GELATIN, made by partial hydrolysis of collagen extracted from the boiled bones, connective tissues, organs and some intestines of animals. Commonly known as Knox Gelatin and Jello, it’s typically used in making desserts.

Lastly, there’s a cooking process that will thicken liquids:

REDUCTION is the most flavorful way to thicken a sauce. This is the process of reducing the moisture content of a sauce by simmering over low heat and letting evaporation take over, which in turn causes the remaining ingredients to become more concentrated. But caution: Too much heat can cause the emulsion to break.

Finally, pureed vegetables and tomato paste make ideal thickeners. They also contribute a pleasing texture and nutrition boost.