Do you know how to produce solidified duck egg yolk used in making moon cake? It is very easy. We learned that when we visited the Tainan Duck Farm, a leisure farm in Tainan, Taiwan.
In photo, the owner is showing newly harvested solid duck egg yolks ready for making moon cake or for some other purposes. The process is like this. They coat the eggs with clay, just like they do in producing salted eggs. For 30 days the clay-coated eggs are stored in a room. After that, the eggs are cracked open, and lo and behold the yolk has become solid. The egg white has become watery and discarded.