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Table I: The Eight Most Common Bacterial Contaminants
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| Name |
Attributes |
Classification |
By Products & Off Flavors |
| Acetic acid bacteria |
Aerobic
Acid tolerant
Hop sensitive |
Gram negative
Rod-shaped
Cocci-shaped
Beer spoiler |
Surface growth
Acidity
Vinegar smell
Ropiness |
| Acetomonas |
Aerobic
Acid tolerant
May form chain |
Gram negative
Rod-shaped
Beer spoiler |
Turbidity
Apple or cider smell |
| Coliforms |
Aerobic & anaerobic species |
Gram negative
Rod-shaped
(both long
and short)
Wort spoiler |
Celery odors
Phenolic odors |
| Lactobacillus delbruckii |
Facultative aerobe
Thermophilic
Will not grow in
hopped wort |
Lactic acid bacteria
Gram positive
Rod-shaped
Beer spoiler |
Acidity |
| Lactobacillus pastorianus |
Anaerobic
Hop tolerant
Alcohol tolerant |
Lactic acid bacteria
Gram positive
Rod-shaped
Beer spoiler |
Acidity
Ropiness |
| Obesumbacterium proteus |
Aerobic
Very common
Only early fermentation |
Gram negative
Rod-shaped
Wort spoiler |
Yeast contaminant
Parsnip flavors |
Pediococcus
("Beer Sarcina") |
Anaerobic
Homofermentative
Superattentuative
Extremely dangerous
Nonmotile |
Lactic acid bacteria
Gram positive
Cocci-shaped
Single cells, pairs,
and tetrads
Beer spoiler |
Turbidity
Acidity
Diacetyl
Ropiness
Sediment |
| Zymomonas spp. |
Anaerobic
Wider range of pH
Tolerant to low temp
Highly motile |
Gram negative
Rod-shaped
Beer spoiler |
Turbidity
Rotten apples
Hydrogen sulfide
Ropiness
Acetaldehyde |
