Learn the science behind:
Nothing better than a lasagna coming out of the oven, bubbling like crazy, with a perfect light brown cheesy top. Even though there are loads of ways to make a lasagna, our favorite remains one with tomato sauce and a creamy bechamel sauce on top.
Lasagna is made best (I find) with home made pasta dough and sauces. None are hard to make, but when doing it yourself you can do it to your own taste. The advantage of using homemade pasta dough is that it’s a lot more flexible and easy to assemble! Since we discussed pasta dough before, let’s discuss the bechamel sauce (especially since the tomate sauce isn’t as sciency).
Before I realized bechamel sauce ‘belongs’ on a lasagna I didn’t really appreciate it too much. In cheap lasagna there tends to be a lot of bechamel sauce whereas I always preferred the tomate sauce. In other words: I always thought it was a cheaper version of lasagna. But, if used in a good ratio, it can enrich a lasagna and I’ve come to quite like it.
So what is a bechamel sauce? It is a thicker gooey white sauce, pretty neutral in taste actually, made with only three ingredients: butter, flour and milk. The flour does most of the work in the bechamel sauce, but do not be fooled by the importance of butter!
Flour is a super versatile ingredient in our kitchen. We’ve explored it many times before. It can be used to give gumbo tons of flavour in a dark roux, thicken your pie filling, make choux pastry and of course is the basis of bread, scones, biscuits and tons of other baked goods.
In some cases the gluten of flour is what we’re looking for, in other cases, it’s the carbohydrates and sugars. In the case of a bechamel sauce, flour thickens the bechamel sauce, giving it the characteristic thick, gooey texture. It’s the starch that does the magic here, starch is one of the components of flour.
Flour + moisture + heat
When flour is mixed in water and heated the power of flour sets in, more specifically, the starch. At higher temperatures the starch will absorb moisture and start swelling. It’s this swelling of the starch that gives flour its thickening power. The thicker granules prevent water from flowing freely and thus it thickens.
More is not better
What’s important to know here, is that this thickening power of flour can actually be reduced over time. If you keep on heating or cooking your flour, it will lose the thickening power. This is what happens when making a dark roux. You heat the flour so long while it’s a roux that it loses this thickening power. Instead, the starch will break down.
Making bechamel – importance of the order of steps & preventing lumps
So it’s the flour that gives bechamel the thickness. But when using flour there’s often a risk of lump formation. Think of making pancake batters. These lumps occur if flour has not been disperserd properly when it’s heated. As long as water and the liquid in which you disperse it are cold, it is easy to mix the two. However, since the starch starts swelling as soon as it get hot it can be hard to mix the two when the liquid is hot. The swelling of the starch will prevent water to travel to the inside of the flour lumps.
So, when making bechamel (or any other sauce using flour as a thickener) you should prevent this thickening of flour, before you have had a chance to mix it in properly. For making a bechamel the ‘inventors’ have found that using butter greatly helps here.
By first melting butter and mixing in the flour, the flour gets covered and coated with the butter. This prevents the formation of lumps. Once the liquid (milk) is added, the flour particles have been ‘protected’ by butter and that way you prevent the formation of lumps.
The butter helps to disperse the flour through the milk. The principle is very similar to the effect used to make choux pastry.
Summarizing all what’s above, here’s a general recipe for any bechamel sauce. Feel free to vary and change bits and pieces to improve, there’s no one perfect bechamel sauce for sure!