All of the Siebel Bry 96 derivatives produce slightly different products because they have all adapted to their propagation environments. Wyeast 1056 does not produce a beer that tastes exactly like cultured Sierra Nevada, which, in turn, produces a beer that tastes slightly different than its parent culture Bry 96.
Yeast cells have two metabolic pathways. In the presence of oxygen and glucose levels below the Crabtree threshold, yeast cells consume a carbon source (e.g., glucose) and produce mostly carbon dioxide gas (CO2) and water (H2O). At glucose levels above the Crabtree threshold, yeast cells consume a carbon source and produce mostly CO2 and ethanol (CH3CH2OH), regardless of oxygen concentration (which is known as the Crabtree effect). The first metabolic pathway is known as the respirative metabolic pathway. The second metabolic pathway is known as the fermentative metabolic pathway.
If we look at respiration and fermentation from a chemical output point of view, it is easy to see that fermentation is the yeast cellular equivalent of incomplete combustion. Yeast cells consume glucose, which has the chemical formula C6H12O6. During respiration, the primary byproducts are CO2 and H2O. During fermentation, the primary byproducts are CO2 and CH3CH2OH.
Contrary to what appears in many older home brewing books, yeast cells do not respire in wort because the glucose level is higher than the Crabtree threshold. All yeast biomass growth in a brewery is fermentative. Respirative (aerobic) growth is significantly more efficient than fermentative (anaerobic) growth.
US-05 produces a beer with the greatest deviation from Bry 96 on the first pitch because it is propagated aerobically in a bioreactor. A bioreactor is device in which the glucose level is held at a steady state below the Crabtree threshold. Oxygen and new medium are continuously added while yeast biomass is removed. It is an extremely efficient process that results in explosive yeast biomass growth. This type of propagation is known as continuous propagation. Wyeast Labs, White Labs, and brewers propagate yeast anaerobically in batches. Aerobic growth is significantly more efficient than anaerobic growth because the respirative metabolic pathway is more efficient than the fermentative metabolic pathway. However, yeast cells that have been propagated aerobically have never had to deal with the stress that ethanol places on their cell walls. The performance difference between US-05 and the liquid offerings narrows on subsequent repitches.
Topic: Yeast taste difference (Read 3362 times)
