By The Foodist
Bob's last post and Jennie/Tikka's comment about using roux in Alfredo sauce got me thinking.
Most of us rarely, if ever, use roux these days. There are a few reasons why:
A) It's time consuming
B) It's fatty/Considered not-healthy
C) It can sometimes be hard to work with
But there are a few cases where nothing else but Roux will do. So what do you do? How do you ensure it works out well for you? Well here are a few steps and hints to ensure that your product comes out tasting good and looking swell.
First, we need to understand what Roux is. Anyone who has taken the basics of a culinary course could tell you that its the combination of a flour and fat. But to really understand how it works we should take a page from that foodie-chemist Harold McGee:
"Flour is about 10% protein by weight, and much of this fraction is insoluble gluten. Gluten aggregations probably get caught in the starch network and so slightly increase the viscosity of the solution, through the pure starches are generally more powerful thickeners overall...
Finally, Fats are usually present in the form of butter, oil, or the drippings from a roast. They do not mix with water or water-soluble compounds, but they do slow the penetration of water into starch granules. Fat does contribute the sensation of the smoothness and moistness to a sauce, and when used to precook the flour in a roux, it coats the flour particles, prevents them from clumping together in the water, and so safeguards against lumps."
Ok so ... in English please?
Here's how I think it works. The gluten in the starch of flour is combined with the fats in the butter, oil, or fats from drippings and bond creating a mushy mess we call "roux." Think of making a basic vinaigrette, you combine oil and acid with a binder to hold the emulsion, same basic principle applies. Cooking the roux allows moisture to evaporate leaving a stronger bind between flour and fat.
So now that we have an understanding of what it is, what's the problem?
There are a few things you need to know when using roux. First off, starch takes awhile to cook away. That floury/starch flavor you get from roux means that it needs to cook longer. Starch needs time to break down leaving only the gluten and fat bond to add viscosity and texture to the product.
Secondly, Roux is very very finicky. It takes a trained eye to judge the correct amount of roux to use. There is no set rule on XX Amount of Product requires XX Amount of Roux mainly because different products are different viscosity to begin with and chemical composition is different between products. For example, chicken stock will generally have less natural thickeners than veal stock made with joints and connective tissue.
The worst part of this is that the only thing you can count on with a roux is time. Allowing a product to cook out the starches and hence thicken the product correctly is the only way to judge if you need more or, worst case, less.
So you're probably asking yourself, Why on earth would I choose to use roux ?
Well, roux imparts a very unique flavor and texture that modern food science has come close to copying but hasn't quite gotten right. It is also safer to use roux to thicken dairy based sauces because of the impartial flavor of roux, cornstarch tends to create an unappetizing look and mouth feel, as does potato starches.
So when do you use roux?
I haven't thickened a sauce with a roux in a long time. Mostly because I don't mess with a lot of dairy based sauces . But if you're making a homemade Bechamel, need to thicken an Alfredo sauce, or want to make a classic veloute (Chicken stock thickened with roux) then there's your chance. But a word of warning, it is almost always best to season a sauce made with roux after you are sure the starches have cooked out and you have your desired thickness, even then its always a good idea to strain the sauce as well in case any wayward flour lumps survived your whisk.
In cases like Jennie/Tikka's Alfredo sauce, it's also best to add the roux to thicken the cream, then add the cheese. This way you prevent the cheese from burning and becoming bitter, just remember to under thicken slightly, the cheese will also act as a thickener.
Hope this helps with any roux related questions and concerns, and remember sometimes the classics are the best!