Thickeners can be tricky, but they can take a meal from ok to Amazing! pretty quickly. Here I will attempt to explain uses, methods, and potential variations of a few types of thickeners.
Corn starch is a very inexpensive and quick thickener, resulting in a slippery and transparent sauce. It is used in stir-frys, gravies, desserts, and even white sauces.
Generally it works by mixing a small amount of corn starch into some water and then stirring that water into the sauce you are making. This eliminates lumps while the starch is in a small volume of water, and helps keep the finished sauce very smooth and lump-free.
A key tip for working with corn starch is to remember ‘Opposites’. If making a hot sauce, the water into which the starch is stirred should be cold. If the sauce is cold, stir the starch into hot water.
Some recipes use the starch directly in the sauce without the first dissolving step. If this is the case, follow the directions in your recipe.
A downside of cornstarch is that it can have a slight sweetness, so you will want to factor that into your recipe if you are cooking “off the cuff”.
Roux is the traditional French thickening method, and is both high in fat and sublimely delicious. Roux are great for savory dishes especially, and make the best gravy (in my opinion). I also use roux in white sauces, creamy soups, and cheese sauces. This method is used in my Baked Potato Soup recipe (pending).
The two ingredients traditionally used in roux are wheat flour (all purpose), and butter, in equal weights. Since not everyone has a food scale in their kitchen, I recommend using a little more flour than butter by volume. As you become more confident making roux, you will know what you want it to look like.
The method involves melting the butter in a small pan and sprinkling the flour over it, while briskly whisking. The goal is to make it completely smooth. Once they are fully incorporated, you will add broth or milk to it, or add it to broth or milk. Hot roux into hot liquid makes the smoothest sauce.
Some recipes will have you saute’ something (chopped onions or mushrooms, for example) in butter, add the flour, whisk, and add the liquid, whisking. This is a really easy way to kill two birds with one stone. You are cooking an ingredient in butter, and you are making a sauce with that butter. I find that the extra ingredients can help break up lumps of flour as well.
An obvious downside to roux is that they are very high in fat. Another drawback is that they can be tricky to get just right. If they are too thick they become like a jelly paste, or they can be lumpy if things don’t go well. I recommend practicing the technique to achieve perfection, and going to the gym afterward. (I couldn’t resist!)
Some recipes call for simple and inexpensive flour thickening. It is often the thickener in things like gravies, pies, and gelled desserts (like the topping in lemon bars). I have also used it to thicken certain white-sauced savory recipes.
If being used in gravy, it is generally sifted slowly into the broth while whisking briskly to eliminate lumps. If in pies, the flour is added to the fruit, stirred to evenly distribute, and then poured into the crust where the liquid from the fruit will actually thin the flour. If in gelled desserts, it’s just stirred into the filling. In some of my white-sauced recipes I have put the flour in a jar with some milk and shaken it hard to remove lumps. In others I have stirred it into sour cream, then added water to thin it. Refer to the instructions in your recipe.
This may seem redundant, but the biggest challenge with using flour is keeping it lump-free. I also personally dislike the blandness it imparts to savory dishes (I was raised on roux gravies). On the plus side, it’s faster than roux and much lighter from a calorie standpoint, making it a better option if you are trying to manage your weight or cholesterol. It’s almost endlessly versatile as well.
As you may imagine, tomato paste is best used to thicken tomato-based sauces and dishes, and is generally (I would say ‘always’ but how can I know?) used in savory foods. It is inexpensive, easy to use, and low fat.
It works best to scoop the paste out of the can into a small bowl and stir some water into it until it is smoothly incorporated. If you are thickening a large batch of something (spaghetti sauce or salsa to freeze or can, for example) it can be scooped directly into the sauce, since it will have lots of time to thin down and be stirred in.
On the down side, it is only for tomato-y foods. This is also a positive, since it removes the question “should I use this, or something else?” entirely. Be aware that tomato paste should not be thinned with water and used as tomato sauce. You can do this, but due to the extensive cooking/dehydrating process the tomato goes through, the flavor isn’t very good.