Respiratory Phase

respiratory phase.

  The second aerobic stage of the fermentation process immediately following the lag period, so called because the yeast draws oxygen from the wort to oxidize a variety of acid compounds. During this stage, six-carbon sugar (glucose) is the first converted into three-carbon acid (pyruvic acid), causing a significant drop in pH; the pyruvic acid is then reduced to activated acetic acid (acetyl CO-A), followed immediately by the Krebs cycle. See also:  fermentation phase; Krebs cycle; lag period.