BREWING BACTERIA ON LMDA 

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