This is just a brief overview on different techniques you can use to thicken certain dishes, usually things like sauces, gravies, and soups. I don’t want to get too into things here just because it’s a topic with a lot of information, so I just want to give you the most basic information. I’m sure, as time goes on, we’ll get into things more in-depth on a need-to-know basis. Yes, I just said “need-to-know” basis, like I’m the James Bond of thickeners or something. If only I were as hot as James Bond.
There are three basic thickening techniques: flour and water, cornstarch and water, and roux (pronounced “roo.” Darn French and their superfluous letters.) Each has its place and its own pros and cons. In both the cornstarch and flour methods, the general rule of thumb is equal parts starch and water, although you’ll definitely find recipes that call for different proportions. And if the recipe tells you to do it differently, do it.
Cornstarch and Water
Cornstarch is finer, silkier, and doesn’t have the protein of flour. It needs to be mixed completely with cold water before being added to boiling liquid, and once added, it needs to be cooked only until the liquid has thickened. If you cook it too long, it will break down and the liquid will lose its thickness. Cornstarch also makes things clear, so keep that in mind when you’re deciding whether to use cornstarch or flour. You’ll find a lot of Asian dishes calling for cornstarch as a thickener. Also, if you’re using cornstarch in a recipe that calls for flour, you’ll need 1/2 as much cornstarch as the recipe states.
Flour and Water
When you use flour as a thickener, you’ll find that it makes your sauce, soup, or gravy thick and opaque. While cornstarch can’t handle being cooked for very long, flour must be cooked in order to release the thickening properties and also to lose the “raw” taste. However, when cooked for a long period of time, the cooking flour will take on a fantastic taste, especially in highly-flavorful dishes like stews and gravies. Only use white flour as a thickener (it’s a protein thing…and a texture thing…”smooth” and “whole wheat” are two words rarely heard together).
Roux is a combination of fat and flour. I live in Roux Country (and also where “roux” is usually pronounced with at least 2 syllables) and can say that most Cajun cooks I’ve talked to hold their roux recipes near and dear to their secretive little hearts. The fat can be butter, lard, vegetable oil, or animal fat and is melted and combined with flour and then cooked to a desired level; very little for something mild like corn chowder or breakfast gravy, or long and dark for something like gumbo or some kind of game stew. Many recipes, especially those for cream-based soups or of French or Cajun origin will call for roux and it’s really not as complicated as it sounds. Basically, you want to melt the fat, whisk the flour in as quickly as possible and make sure you get any lumps out, and then, when you start adding additional liquid, make sure the liquid combines well with the roux so you don’t wind up with lumpy roux bits in your final dish.
So here are the rules of thickeners:
1. Cornstarch and flour are mixed with water and added to hot liquids; roux is cooked with fat first and the liquids are added to it.
2. Work quickly to remove lumps before adding (or adding to) any additional ingredients.
3. Cornstarch can’t be cooked for very long; flour must be cooked for awhile.
4. Cornstarch produces a clear result; flour makes it opaque.
5. Use twice as much flour as cornstarch (and half as much cornstarch as flour) if you’re substituting one for the other.