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Lecture

MIP 300 Lecture Notes - Pediococcus, Microbiological Culture, Gram Staining


Department
Microbio, Immun, Pathology
Course Code
MIP 300
Professor
Erica Suchman

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10 May
Yeast Management at New Belgium
Maintain pure cultures that may be used for fermentations
Propagate yeast to keep fermentations consistent and clean of contamination
What is meant by pure culture
A single strain of a yeast species grown in isolation from other yeast strains and free
from any microbiological (e.g. bacterial) contaminants
Pure culturing of brewing yeast
Pure cultures = consistent products
Technology over 100 years old
Culturing must be free of contaminant microbes
Pure yeast cultures can be isolated as individual colonies (streak plating)
Propagation of brewing yeast
Why propagate yeast?
To produce sufficient yeast in good physiological condition
To avoid mutations
Minimize contaminations
Prevent problems (sluggish fermentations, off flavors like H2S/diacetyl,
maltotriose uptake, altered flocculation patterns)
Mutations in brewing yeast
Yeast mutations are relatively common
The most frequent mutations are
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Tendency to lose flocculence
Loss of ability to ferment maltotriose
When to propagate yeast?
Depends on the brewery
At New Belgium, ale yeast is typically repitched for generations, and lager yeast for up
to 5 generations before a new propagation
Yeast Propagation at New Belgium
Laboratory propagation
Lab propagations begin on an agar slant
They are then transferred to shake flasks
Finally the propagation is moved to a ½ bbl keg
Key considerations
Aseptic technique
Propagations stepped up at maximum 1:10 volume increments
Aeration
Temperature
Plant propagation of yeast
Objectives
Sufficient yeast biomass in good physiological condition
Rapid growth
Enough yeast for pitching
Key considerations
Wort – sterility, type, gravity
Conditions – hygiene, aeration/mixing
Temperature – gradually decreases
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