Why Tangyuan Float When Cooked | Generated by AI
When tangyuan (汤圆) float to the surface after cooking, it’s due to density changes caused by heat.
Here’s what happens:
Before cooking:
- The tangyuan are denser than water, so they sink to the bottom
- They’re compact glutinous rice balls, often with filling inside
During cooking:
- The hot water heats the tangyuan throughout
- As they heat up, the starches in the glutinous rice flour gelatinize (absorb water and swell)
- Small air pockets and water vapor form inside the tangyuan
- The filling (if present) also heats and may release some steam
Why they float:
- The expansion from heating and the trapped air/steam pockets increase the tangyuan’s volume
- This makes them less dense overall
- When their density becomes less than water’s density, buoyancy pushes them upward
- They rise to the surface and float
This floating is actually the traditional sign that tangyuan are done cooking! Once they float and have been bobbing at the surface for a minute or two, they’re usually ready to eat. The same principle applies to other dumplings like Italian gnocchi - floating indicates they’re cooked through.