There’s a million ways to thicken sauces, some that have an impact on flavour and others that don’t… here I’ll share my experiences with my favoured methods, and the failures and successes I’ve had with them.
A roux is a mixture of a fat (usually butter) and flour in equal weights that’s cooked until the raw flour taste is gone. Rouxs can then be added to your sauce, but make sure the sauce isn’t too hot or else the roux can get lumpy. My biggest problem with this method is that it’s a bit of a hassle, and adds fat to the sauce. I also struggle at times to know just how thick the final sauce will get after adding the roux. However, it is the most traditional of thickening methods and is in of all classic French sauces (Bechamel, Demi-glace (Espagnole) and Veloute) Great about Rouxs is that it’s flexible, a dark roux (one that’s spent a lot of time on the heat) will add a rich nutty flavour to your sauce, while a light one (not cooked for long) will be more delicate and subtle.
I came across this ingredient by accident, it’s basically a starch that can be added to sauces to thicken them, almost directly (just dissolve a teaspoon in a quarter cup of water). Only caveats is, use it sparingly, as too much of it will over thicken the sauce and will really come out in the taste. Make sure your sauce isn’t too hot or else the arrowroot won’t thicken well. Great replacement for a Roux as it doesn’t really cloud up your sauce (can be used to thicken a jus), is tasteless and doesn’t have this nasty cornstarch shine to it.
Hard to think of as just a thickener because: a. it doesn’t thicken very well and b. it affects taste so much. Cream must always be seen as an ingredient more than a thickening agent, and cream based sauces must always be runnier than you imagine; the sauce will always be runnier than the original consistency of the cream, otherwise it must have over-reduced. A good test of how thick a cream sauce should be is the “coat the back of a wooden spoon” test, and the “pour a dash of sauce on a plate, run a spoon through it, if it divides and comes back, should be done” As with all other sauces, just make sure not to add the cream to a really hot sauces, and don’t take the temperature of the thickened sauce beyond a simmer.
Used as the base and thickener of mayonnaise and hollandaise sauces, egg yolks can be used in other sauces (I feel it goes well with creamy sauces a la carbonara) as well. Egg yolks add a nice richness to sauces, just make sure not to add them directly to a sauce, the easiest way to do it is to add some of the actual sauce (warm, not hot) to the yolks and whisk them together, once a uniform slurry is formed, slowly add the slurry to the sauce, whisking it in well. Never take the sauce beyond a soft simmer otherwise you’ll end up with scrambled eggs in your sauce.