One of the traditional dishes we took on in Modernist Cuisine at Home is classic mac and cheese. While we have always loved this family staple, there is an inherent problem with traditional preparations: all of the virtues of using good cheese are lost when you make a cheese sauce with flour and milk, as in a traditional béchamel sauce, the standard in nearly all macaroni and cheese recipes.
Cheese is an emulsion of dairy fat and water, but that emulsion tends to break down when it gets hot. The starch particles and milk proteins in béchamel act as emulsifiers, but they aren’t very good at their job and result in poor flavor release. So, either you sacrifice the flavor of the cheese by adding far too much béchamel, or you dilute the cheese less at the cost of greasiness. We solve this problem with a little emulsion science and the use of sodium citrate.
Our modernist version of mac and cheese owes its chemistry to James L. Kraft, who in 1916 patented the first American cheese slice. He showed that sodium phosphate keeps the water and fat droplets mixed when the cheese is melted. We use sodium citrate, which has the same effect and is easier to find. The resulting texture is as smooth as melted American cheese, but as complex and intense in flavor as any of your favorite cheeses.
adapted from the recipe for Mac and Cheese on page 310 of Modernist Cuisine at Home