Pisty_Pete
Well-Known Member
I was wondering if anyone could help clarify the relationship between ester production and cell growth/Acetyl CoA availability.
Acetate ester production requires Acetyl CoA and Acetyl CoA is also involved in/required for cell growth. I've read, from various sources, that Acetyl CoA is limited in cells and that if cells are actively growing it is mostly tied up in growth (ie. not available for ester formation). Accordingly, more cell growth = less ester formation.
I've also read (on Wyeast's webpage for example), the opposite - that increased cell growth (ie. from under-pitching) results in higher ester formation:
"The pitch rate will have a direct effect on the amount of cell growth during a fermentation. Cell growth decreases as pitch rates increase. Ester production is directly related to yeast growth as are most other flavor and aroma compounds.
A low pitch rate can lead to:
Excess levels of diacetyl
Increase in higher/fusel alcohol formation
Increase in ester formation
Increase in volatile sulfur compounds
High terminal gravities
Stuck fermentations
Increased risk of infection
High pitch rates can lead to:
Very low ester production
Very fast fermentations
Thin or lacking body/mouthfeel
Autolysis (Yeasty flavors due to lysing of cells)
With some beer styles, where a complex ester profile is desirable (German Wheat) it can be beneficial to under pitch...."
This seems contradictory to the limited Acetyl CoA/ester production is negatively correlated with yeast growth theory above. Any thoughts??
Acetate ester production requires Acetyl CoA and Acetyl CoA is also involved in/required for cell growth. I've read, from various sources, that Acetyl CoA is limited in cells and that if cells are actively growing it is mostly tied up in growth (ie. not available for ester formation). Accordingly, more cell growth = less ester formation.
I've also read (on Wyeast's webpage for example), the opposite - that increased cell growth (ie. from under-pitching) results in higher ester formation:
"The pitch rate will have a direct effect on the amount of cell growth during a fermentation. Cell growth decreases as pitch rates increase. Ester production is directly related to yeast growth as are most other flavor and aroma compounds.
A low pitch rate can lead to:
Excess levels of diacetyl
Increase in higher/fusel alcohol formation
Increase in ester formation
Increase in volatile sulfur compounds
High terminal gravities
Stuck fermentations
Increased risk of infection
High pitch rates can lead to:
Very low ester production
Very fast fermentations
Thin or lacking body/mouthfeel
Autolysis (Yeasty flavors due to lysing of cells)
With some beer styles, where a complex ester profile is desirable (German Wheat) it can be beneficial to under pitch...."
This seems contradictory to the limited Acetyl CoA/ester production is negatively correlated with yeast growth theory above. Any thoughts??