Twelve hours fermenting and the wort (pronounced wert) is showing signs of activity. At this point the yeast has gathered enough energy to begin the reproduction and fermentation cycle which is what you see here. The yeast churns out this foamy head called kraeusen (pronounced kroy-zen). It’s a very bitter resin that contains “fusel” oils which are known to contribute to “beer headaches.” Kraeusen can either be allowed to fall back into the beer or automatically removed via a “blow-out” tube as I am doing here. Once the activity subsides the tube will be replaced with an air lock until fermentation is complete.