In Part I of this series on food thickeners we looked at a variety of different items that can be used for thickening. In this part we will be focusing exclusively on flour, as a thickener, as that is what most people turn to when something needs thickening. As stated in Part I, flour is not the thickener of choice for everything. Fruit sauces, clear soups, certain meat glazes, and many pie fillings are just a few examples of items that do not do well being thickened with flour. On the other hand gravies, many sauces and a whole variety of soups are best thickened with flour, or more specifically a roux.
There are four main methods for incorporating flour into a sauce or soup to thicken it. These four ways are 1.to make a flour slurry made up of flour and enough cold liquid to form a thin paste, 2. to sprinkle flour into a pan of sautéing vegetables or meat and stirring it into the excess fat (what the French calls singer), 3. to make a roux, or 4. to make a beurre manie, a paste of flour and butter kneaded together. You will notice that the one way not to thicken something is to just add flour directly to the simmering liquid. This is one sure way of making a lumpy sauce full of little ball of flour. What happens is this-as you toss the raw flour into your simmering sauce the flour tends to clump together. As the flour on the outside of these clumps comes in contact with the hot liquid the starches immediately gelatinize forming a barrier around all the other starch molecules, not allowing them to gelatinize and expand. At this point no matter how much you whisk the sauce you will never get all the lumps out and much of the flour goes to waste without having done its job. What all the proper methods have in common is the fact that they work by separating the starch molecules, allowing them to expand and do their job as they gelatinize. Let's look at the four methods individually.
Many of you will probably remember your grandmother using a flour slurry to thicken her gravies. It is a method seen quite often, but it is not necessarily the best option. Sure it thickens sauces and soups without lumps, most of the time, but you can get a better flavor and texture by using a roux.
The method of sprinkling flour into the sauté pan, or singering as the French say, is nothing more than making a roux right in the pan you are cooking in. This method is often employed when you want the flavor of the fat to be an important part of the finished dish. A great example of this method is that Southern classic, Sausage Gravy. Once the sausage has been browned flour is added directly to the pan to make a roux with all that flavorful fat that rendered from the sausage.
A Beurre Manie is often used when making "pan sauces" at the last minute. Adding this flour and butter paste to a quick pan sauce thickens it and gives the sauce a nice sheen while enriching the sauce with the butter. These sauces must not be cooked longer than a minute or 2 or the starchy taste of the flour will start to become noticeable and the sauce will then need to be cooked for a minimum for 15-20 minutes more to get rid of the raw starchy taste.
That leaves roux, probably the most used of all these methods. Unfortunately many people don't really understand this relatively simple, commonplace item and they end up with soups and sauces that are lumpy and starchy tasting, but by following the guidelines below all that will be remedied. First off a roux is nothing more than a mixture of flour and fat that is then cooked. The fat can be butter, oil, lard, bacon fat or any other fat, though butter is most commonly used, especially in sauces where it helps to enrich the sauce. There are 4 main stages to roux.
Stage 1. White Roux
This is where the flour and fat are mixed together and quickly cooked for 5 minutes to start cooking out some the raw starch flavor.
Stage 2. Blonde Roux
The roux is cooked for about 20 minutes, which allows the flour to lose more of its raw taste. The mixture also tends to thin out a little as the start begins to cook.
Stage 3. Light Brown Roux
At this stage the roux darkens to a light brown which imparts a slight nutty and toasty flavor to a sauce.
Stage 4. Dark Brown Roux
It is at this final stage in the roux that provides a deep, rich nutty flavor and just a slight hint of bitterness to a dish. It also provides a good amount of color. This is type of roux is commonly used in Cajun cooking. Gumbo will not have its familiar taste without a properly made dark roux added to it.
All of these rouxs start out with equal amounts of flour and oil, by weight. How much of each all depends on how much liquid you have to thicken and how thick you want it. For 1 gallon of sauce or soup you will need 12oz of roux (6oz flour & 6 oz oil) for thin, 16oz of roux for a medium body, and 24oz for a thick soup or sauce. Once a roux is added to the liquid, it must be brought up to a boil for it to thicken completely. After boiling, return the liquid to a simmer and cook for, at least, 15-20 minutes to cook out the raw starchy taste of the flour. Again butter is the most often used fat for making roux because of the richness it brings to dishes, but other fats are always acceptable. In fact, when making darker rouxs it is better to use clarified butter or vegetable oil as the solids in whole butter will burn at the high temperatures that dark rouxs get cooked to. Talking about dark rouxs there are two things to keep in mind. First of all, once the roux starts to darken turn your heat to medium low and stir constantly. If at any time you see dark flakes in the roux it is burnt and will need to be started again. Secondly, brown rouxs are very, very hot, were talking liquid napalm. Not only will it burn badly if it splatters, it also has a tendency to stick. Burns from brown rouxs are not pleasant so please be careful. Another thing that must be kept in mind when working with roux, never add hot roux to a hot liquid. You will get lumps as the starch will gelatinize too quickly for the fat to do its job. Best bet is to add warm roux to a liquid below simmering then bring it up to a boil from there. Flour, used as a thickener, tends to breakdown when frozen and thawed so if you freeze a flour thickened soup you might have to re-thicken it when you reheat it. Finally, as rouxs are cooked to a darker and darker level they lose their thickening power. In general, a dark brown roux has about ¼ the thickening power of a white roux.
Well, I hope this series has answered a few questions about thickening agents, especially when to use certain starches for thickening. And now that you understand what makes a gravy lumpy it's time to go out and show Grandma a thing or two. Enjoy!
Check out Making Sense Of Food Thickeners Part I