I'm reading a recipe for a Sanctification clone, which is one of Russian Rivers Blonde Sour Ales. The recipe for the yeast read as such
Brettanomyces bruxellensis culture, Wyeast 3112 or White Labs WLP650 (3 qt./ starter)
Brettanomyces lambicus culture Wyeast 3526 or White Labs WLP653 (1 qt/ starter)
Lactobasillus delbrueckii culture, Wyeast 4335 bacteria (3 oz/ starter)
Then it instructs to "pitch bottom half" of yeast starters. Ferment starting at 72 degrees.
Any ideas on what any of this means? If I'm only pitching the bottom half, then how much exactly is "the bottom half"?