ASBC_Fishbone_Ie.pdf

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YEAST MANAGEMENT PROCESSES IMPACTING YEAST VIABILITY & VITALITY: ACID WASHING
Processing Parameters
Chilling yeast/acid
before mixing (+)
Yeast too viscous, slow
equilibrium of acid (-). Get
correct % solids.
Adding acid before brink is filled
with yeast (-)
Design Considerations
Chlorine dioxide
treatments at pH 3.0 for only 10 min, effective &
less harmful to yeast than phosphoric acid treatments.
Contact times > 2 hr (-)
pH's < 2.0 (-), keep at 2.0 - 2.2 (+)
Stirring while acid washing (+)
Shaft & impeller mixers (+)
Once washed, wash every generation (+)
Contact with undiluted acid (-)
Mixers with only local effect (-)
Wash "unhealthy" yeast (e.g. from slow
fermentation or stored too long) (-)
Temperatures above 0
0
C (-)
Magnetic type stirrers (-)
Yeast originating from fermentations exceeding 8%
ethanol (v/v) (-)
Acid conditioning at pH 3.0 (+)
Effect on Yeast
Viability & Vitality
Pitching immediately after washing (+)
Use of food grade acid, preferably phosphoric or citric (+)
Storage of acid washed yeast (-)
Ale yeast less acid washing tolerant than lager yeast .
Pitching yeast temp
greater than 3-5 C than wort temp
("cold
shock"
slows growth) (-)
McGill:
Exposure to shear forces during pumping, agitation and
centrifugation of yeast slurries has a negative impact on yeast quality.
Negative effect is aggravated by acid washing (up to six-fold), with use
of phosphoric acid leading to larger losses than water alone. Addition of
0.75% ammonium persulfate to a pH 2.3 phosphoric acid wash solution
increased viability when exposed to mechanical shear.
0
Less vital yeast more sensitive to shearing from
agitation
Pitching
Bill of Materials
ASBC No. Ie
(Casey;
June/05)

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