That's not brown head. The brown head is the first head that forms during fermentation. It usually contains trub and particulate matter. The customary practice in UK breweries that employ open fermentation is to skim and discard this head. The clean yeast head forms after the brown head is skimmed (or falls back into the beer). Yeast is skimmed several times during fermentation. Some of the yeast is collected for repitching while the majority of it is discarded. The practice is covered @ time 1:12 in the video linked below.