Wine fining is the process of removing sediment from a wine before it is bottled, resulting in a clearer liquid. A fining agent is mixed into the wine that reacts with the floating sediment and together settles to the bottom of the tank or barrel. The remaining deposit is then racked off.
For centuries, Bordeaux has traditionally used egg white as a fining agent for its red wines. However, since only the egg white and not the yolk (yellow part of the egg) was being used, this resulted in a lot of yolk being thrown out—which the Bordelais saw as a shameful waste.
So, along came the idea to make canelés… those molded custard pastries with a caramelized crust that are as commonplace in Bordeaux as the wine itself (and now we know why!)
Source: Stephane Laborie, visiting professor, INSEEC Bordeaux