Microbe Overview: Yeast, Brett, Pedio, and Lacto

Earlier this year, the AHA requested some info on the various microbes involved in sour beer production for a post they were working on (Sour Microbes: Yeast and Bacteria Explained). I wrote up the summaries below for brewer's yeast, Brettanomyces, Lactobacillus, and Pediococcus to help them out. Nothing ground breaking, but since I had it already hopefully other people might benefit form the overview (without the ultra-nerdy details of chapter 4 of American Sour Beers)!

Brewer’s Yeast - Saccharomyces cerevisiae (ale yeast) and S. Pastorianus (lager yeast)
Type: Yeast - Order Saccharomycetales (Family: Saccharomycetaceae)

Fermentables: Primarily glucose, fructose, sucrose, maltose, and maltotriose (also mannose, galactose, and raffinose. Lager yeast also can ferment melibiose.)

Important products: Ethanol, carbon dioxide, esters, and phenols (POF+ strains – mostly Belgian and Hefeweizen)

Oxygen: Beneficial for growth

Ideal temperature: 45-95F (strain dependent)

Speed: Fast

IBU Tolerance: High

Overall: Brewer’s yeast protects the wort and sets the stage for a traditional slow-moving mixed-fermentation duo of Brett and Pedio.

Brett - Brettanomyces bruxellensis (aka B. lambicus)/B. anomalus (aka B. claussenii)
Type: Yeast - Order Saccharomycetales (Family: Pichiaceae)

Fermentables: Primarily the same as Saccharomyces, but in addition dextrins up to 9-glucose chains. Some strains (beta-glucosidase enzyme positive) are capable of fermenting lactose, cellobiose (wood sugar), and gylcosides (from hops, spices, and fruit – which releases aromatics)

Important products: Ethanol, carbon dioxide, esters (create and destroy), phenols (converts what brewer’s yeast leaves behind into funkier forms), and tetrahydropyridines (toasty to mousy)

Oxygen: Beneficial for growth, but leads to acetic acid production

Ideal temperature: 58-85F (strain dependent)

Speed: Slow

IBU Tolerance: High

Overall: Works well on its own with a large enough pitch, or in tandem with any of the other microbes listed. Brett doesn’t sour the beers you brew, it makes the sour beer you brew delicious. Can do some of its best work without malt carbohydrates available to ferment (especially during bottle conditioning). More fermentables allow the production of more esters, but these fruity flavors are not driving traditional funky “Brett” character.

Lacto - Lactobacillus delbrueckii/L. brevis/L. buchneri/L. plantarum etc.
Type: Bacteria – Family Lactobacillaceae

Fermentables: Some species can only ferment relatively simple sugars, while others can ferment dextrins.

Important products: Lactic acid, ethanol, and carbon dioxide

Oxygen: Usually aerotolerant (doesn’t use oxygen, but isn’t harmed by it)

Ideal temperature: 70-115F (strain dependent)

Speed: Really fast

IBU Tolerance: Low to very low

Overall: Lacto is capable of sour a beer within 24-48 hours if given free reign. However, too much acidity can cause less desirable performance for the microbes that follow. Most strains do not thrive after primary fermentation is complete.

Pedio - Pediococcus cerevisiae et al.
Type: Bacteria – Family Lactobacillaceae

Fermentables: Complex sugars, some species are even capable of metabolizing starch.

Important products: Lactic acid, exopolysaccharides (EPS), and diacetyl

Speed: Really slow

Oxygen: Usually microaerophilic (prefers oxygen at lower than atmospheric concentration)
Ideal temperature: 60-80F (strain dependent)

IBU Tolerance: Moderate

Overall: Pedio should be used with Brett in most cases to clean up the EPS and diacetyl. Won’t lower the pH as quickly as Lacto, but can reach a lower final pH given enough time and complex carbohydrates.

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