Pitching

Pitching is simply adding yeast, whether dry, liquid, or from a starter, to wort that has already been cooled to an appropriate temperature. It marks the transition from wort to beer, since this is the moment fermentation actually starts, and everything before it, the mash or extract steep, the boil, the chilling, is preparation for this single step.

Getting pitching right involves more than dumping yeast in: wort needs to be cool enough that heat will not shock or kill the yeast, and it should be at or near your intended fermentation temperature so the strain starts in the right range from the beginning. Pitching an adequate amount of healthy yeast for the batch size and gravity also matters, since underpitching leads to a slow, stressed fermentation while overpitching can strip some flavor character.

A common mistake is pitching into wort that is still noticeably warm, killing off a portion of the yeast before it gets going, or pitching a single small packet into a big, high-gravity batch that really calls for a larger amount or a yeast starter. Aerating the wort well right before or during pitching also helps healthy yeast get established quickly.