Bacteria

Occurrence in brewery environments

Off flavour/aroma and odour

Visual poilage effects

Metabolic products

Acetic acid bacteria [2] [21] [24] [26]

Acetobacter

Wort, beer dispenses and cask condition ales and barrel aged ales, brewery biofilm.

Sour, vinegar

Haze, Ropiness

Acetic acid

Glucanobacter

Wort, beer dispense and cask condition ales

Sour, vinegary

Haze

Acetic acid, acetate

Zymomonas

Primed beers

(not found in lagers)

Fruity, rotten apple, rotten egg, sulphudic

Haze

Ropiness

Acetaldehyde and H2S

Enterobacteriaceae [26]

Obesumbacterium

Pitching yeast and fermenting wort

Parsnip, sulphury

Haze

Dimethyl sulphides (DMS), diacetyl, higher alcohols and N-nitrosamines, acetoin

Citrobacter

Brewing liquor , fermenting wort

Parsnip, sulphury

Dimethyl sulphides (DMS), diacetyl, lactic acid, acetaldehyde

Rahnella

Pitching yeast, Early stages of fermentation (wort)

Fruity, sulphury,

-

Dimethyl sulphides (DMS), diacetyl, methyl acetate, ethyl acetate

Klebseilla

Fermenting wort, biofilm

Unpleasant odour

-

4-vinylguaicol, Dimethylsulphides (DMS), diacetyl.

Obligatory anaerobes [72] [76] [77] [99]

Pectinatus

Low alcohol unpasteurised beer, beer filling area, biofilm

Rotten egg, unpleasant odour

Turbidity

Acetic acid, propionic acid, lactic acid, succinic acid, H2S, acetoin, methyl mercaptan and other sulphur compounds

Megasphaera

Low alcohol, unpasteurised beer, beer filling area, biofilm

Unpleasant odour

Turbidity

H2S, butyric acid, isobutyric acid, caprioc acid, valeric acid, isovaleric acid.

Selenomonas

Pitching yeast

Unpleasant odour

Turbidity

Acetic, lactic, and propionic acids.

Zymophilus

pitching yeast or brewery waste

Unpleasant odour

Turbidity

Acetic acid and propionic acid