Amylose. Molecular structure. Retrogradation. And why some foods with sauces are best served hot.
One of my favorite Spanish tapas is croquetas (also commonly called croquettes). They are best served and eaten hot. This is especially so if the filling has been made based on a sauce that has been thickened, such as Béchamel. Eat it hot, and we get a warm and oozy interior. Eat it cold, and the sauce and filling begin to feel too thick and even semi-solid.
Why does this happen? It has to do with the long, straight-chain molecule amylose, and its behavior when cooked and cooled.
We start with the flour, which is used to make the roux (pronounced “roo”) that is then used to make Béchamel. As we cook the roux, starch granules in the flour begin to take in water, eventually bursting and leaking amylose and amylopectin, the two components of starch.
The long amylose straight chains line up and cross-link with one another to form an entangled 3D fishnet that traps water and swollen starch granules (find out why and more about roux in the 1-Minute NomNom “Thick and saucy between the sheets”).
As a rough analogy, you can think of this as a fishnet of small and large balloons. The different balloons are filled with either water or gels (since the starch granules are swollen with water), giving the roux and its sauces a viscous and paste-like texture.
When the sauce is warm or still heated, this 3D fishnet has a fairly loose structure. As it cools though, the amylose and amylopectin molecules begin to realign themselves. This process, called retrogradation, can be thought of as the amylose and amylopectin molecules trying to get back into a more organized structure. When they do, they squeeze out water in the process (this is called syneresis).
Hence the sauce is now more gel than water in the 3D fishnet. The outcome is the sauce becomes less liquid and more semi-solid. And this is why our sauce-filled croquettes are less oozy, smooth and yummy when we eat them cold. The same is true for any foods made with such sauces, such as lasagna, which is often also made with Béchamel sauce.
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photos: in order – depositphotos/edu1971; ajafoto; coolfonk; jacklondon