|
Courtesy of Sun Lee, Coors Brewing Company, Golden
CO
 
Acetobacter oxydans
Enterobacter aerogenes
Enterobacter cloacae (I)
Enterobacter
cloacae (II)
 
Escherichia coli
Obesumbacterium proteus
 
Lactobacillus brevis
Lactobacillus pastorianus
Lactobacillus plantarum
Pediococcus cerevisiae
 
Zymomonas anaerobia
mixed
genera of bacteria
Acetic
Acid Bacteria (Acetobacter,
Acidomonas)
Gram-negative, strictly-aerobic rods common in plant material such as
fruit and grain. Normally encountered in stored or fermenting wort and bottled beer.
Produce acetic acid, which lowers pH and lends a vinegary flavor/odor. Recommended limit:
5 per 1-ml sample or per 100-ml yeast-free sample.
 Colony Color: greenish-blue
Colony Size: 1-2mm
Colony Texture: smooth
Changes media color or cloudiness?: YES
Bubble formation when exposed to peroxide? YES
Turns royal purple when exposed to oxidase reagent? NO (Acetobacter), YES
(Acidomonas)
Enteric
Bacteria (Citrobacter,
Enterobacter, Hafnia, Klebsiella, Obesumbacterium)
Gram-negative, facultatively-anaerobic (except Obesumbacterium, which is a strict
aerobe) rods common in water, soil, and plant material. Normally encountered in stored and
fermenting wort. Produce sulfur compounds, fusel alcohols, phenolics and acetaldehyde,
which cause a variety of off-flavors/odors. Recommended limit: 8 per 1-ml sample or per
100-ml yeast-free sample.
Colony Color: greenish-blue, yellowish-green
Colony Size: 2-5mm, may spread to cover entire plate
Colony Texture: smooth, slimy
Changes media color or cloudiness?: NO
Bubble formation when exposed to peroxide? YES
Turns royal purple when exposed to oxidase reagent? NO (all but Obesum), YES (Obesum)
Lactic
Acid Bacteria
(Lactobacillus, Pediococcus)
Lactobacillus (rod) and Pediococcus
(coccus) are gram-positive, facultative
anaerobes common in plant material such as fruit and grain. Encountered in all stages of
brewing. Produce lactic acid, which lowers pH and lends a tart, sour flavor/odor.
Recommended limit: 3 per 1-ml sample or per 100-ml yeast-free sample.
Colony Color: yellow-green (Pedio), white with bluish center (Lacto)
Colony Size: 1-3mm
Colony Texture: smooth (Pedio), rough or smooth (Lacto)
Changes media color or cloudiness?: YES
Bubble formation when exposed to peroxide?
NO
Turns royal purple when exposed to oxidase reagent? NO
Other
Bacteria (Zymomonas)
Gram-negative, facultatively-anaerobic rods, common in water, soil and plant material.
Normally found in areas where there is little or no oxygen, such as in bottled or cask
beer and in CO2 recovery systems. Tolerates up to 10% alcohol. Rare in microbreweries.
Produces sulfur compounds and acetaldehyde. Recommended limit: 5 per 1-ml sample or per
100-ml yeast-free sample.
Colony Color: bluish-green
Colony Size: 1-2mm
Colony Texture: round, shiny
Changes media color or cloudiness?: NO
Bubble formation when exposed to peroxide? YES
Turns royal purple
when exposed to oxidase reagent? NO
|
