Dumplings and Density: A Culinary Physics Exploration | April 18 2025, 18:08

Suddenly, it hit me – why not have some dumplings? So now, for the second day in a row, I’m devouring dumplings, with three different kinds in the fridge already. Plus, I bought some herring, and Nadya, without coordinating, also brought some. The fridge is surprised; it hasn’t seen either in a long time.

So, while I eat another serving, I’m googling why dumplings float. It’s not trivial, by the way.

Overall, the physics of this floating process is complex. They don’t float just because. Let’s start with the dough. It contains starch which absorbs water and swells (gelatinization), increasing the volume. Inside, the proteins in the dough denature, creating a more rigid structure. Some water evaporates/boils, forming bubbles. Result: the density of the dough decreases, aiding the floating. Meanwhile, the proteins in the meat also denature, become denser, and release moisture, decreasing the meat’s volume. The fat melts. Thus, for the meat itself: density increases, which counters the floating. Moreover, water penetrates inside the dumpling where it wasn’t before, also acting against the floating, as it simply becomes heavier. But the moisture released from the meat (juice) and water in the meat itself can boil, forming steam bubbles inside the filling. These bubbles offset the densification of the meat, and overall density of the filling also decreases (or remains the same).

In the end, the reduction in density of both the dough and the filling (due to the bubbles) leads to a decrease in the overall density of the dumpling, making it float.

Salt barely affects the cooking speed. Although salt raises the boiling point of water (Raoult’s law), to significantly speed up cooking, you’d need to add so much (10g per 2L) that the dumplings would become unbearably salty. In normal amounts, salt is just for taste.

Also, there is such a phenomenon as osmosis which is the reason for the tasty broth. Water penetrates inside the dumpling through the porous dough (osmosis), making the filling juicier. Substances from the filling leach into the water, making the broth tastier and fattier.