What does "percolating" mean here?

[NewHopeR]

Context:

When Will Pacquiao and Mayweather Fight?

A phone conversation between Floyd Mayweather Jr. and Manny Pacquiao last week was an encouraging sign for the longest percolating bout in fistic history—until it wasn't.

[BobK]

Context:

When Will Pacquiao and Mayweather Fight?

A phone conversation between Floyd Mayweather Jr. and Manny Pacquiao last week was an encouraging sign for the longest percolating bout in fistic history—until it wasn't.

It's a variation on the metaphor 'boiling', used of a competition or dispute that goes on for a long time.Instead of a kettleboiling, the image is of a cofee percolator. (There may also be the implication that the process is intentional and preparatory.)

b