How to feed your bugs

For those who are really into sour beers and enjoy all of the other flavours they can produce, the information below will help you create the sugar profile needed to make sure these organisms thrive and produce the desired outcome. 

Saccharomyces cerevisiae (ale)

Saccharomyces pastorianus (lager) (hybrid of S. cerevisiae and S. eubayanus)– Fungus

 Normal Habitat:

-          Ripe fruit skins


 -          Aerobically – glucose, maltose, fructose (growth phase)

-          Anaerobically – sucrose, dimethylsulphate (DMS), acetaldehyde


 -          Cannot use nitrate

-          Needs magnesium, iron, calcium and zinc

-          Optimal pH 4.4 – 7

-          Tolerant up to 15% alcohol

 Producing ideal conditions

 -          Low temperature mashing (149-152)

-          Long mash times (60+ minutes)

-          Oxygenate wort prior or just after pitching

-          Don’t use only reverse osmosis water (not enough nutrients)

-          Protein rest with undermodified malts to release free amino nitrogen


-          Main species of yeast that brewers use to turn wort into beer. Flocculation, temperature preferences, esters and phenols produced vary with the exact subspecies. In general, lower mash temperatures produce a more fermentable wort, whereas higher temperatures (below 168) produce a less fermentable wort and leave residual sugars and body. Lower fermentation temperatures tend to produce phenols if the pitching rate is low. Higher temperatures produce more esters.

Brettanomyces bruxellensis – Fungus

Normal Habitat:

 -          Ripe fruit skins


 -          Complex sugars, glucose, ethanol


 -          Optimal temperatures between 25-32 C

-          Temperature has no effect on products, only speed

-          Optimal pH 3.8 – 7

-          Tolerant up to 13% alcohol

 Producing ideal conditions

 -          Keep temperatures stable between 25-32 C

-          Higher mash temperatures (156-160) – leaves something for the Brettanomyces to eat after the Saccharomyces have finished

-          Allow lactobacillus to lower the pH first or in conjunction.


-          Responsible for the majority of the “funk” flavours, but will produce a small amount of acetic acid in the presence of oxygen. Takes a much longer time to complete fermentation than Saccharomyces and tends to eat what Saccharomyces will not.


Enterobacter cloacae – bacteria

Normal Habitat

-          common gut microbe exists everywhere including water and food.


 -          glucose, lactose, fructose, sucrose, maltose


 -          Optimal temperature of 37 C

-          Does not reproduce as rapidly without the presence of oxygen

-          pH range from 4-7

 Producing ideal conditions

 -          Keep temperatures stable at 37. A few degrees above this will kill the bacteria.

-          Will eat pretty much any wort as long as they aren’t outcompeted by other organisms.


-          Will produce vomit-like odours and flavours if allowed to propagate too much. Usually only desirable in very small amounts. Most brewers keep the temperature above 37C in order to promote the growth of Lactobascillus and discourage the growth of Enterobacter. A small amount, however, will produce some funk in conjunction with Brettanomyces


Lactobascillus delbrückii, acidophilus, lactis -bacteria

Normal Habitat

-           grain, dairy


-          A variety of long chain sugars, including lactose and acetolactate


-          Optimal pH 3.8-7

-          Optimal temperature +37C

-          Extremely sensitive to Alpha Acids in hops

 Producing ideal conditions

 -          Keep pH low to reduce competition

-          Use minimal hops or aged hops. Keep IBU below 10

-          Keep temperature above 37 to reduce competition


-          Produces the majority of the sourness in sour ales. Because of the very limited conditions it needs to survive and thrive, the amount of sourness can controlled relatively easily. Two main methods of propagating Lactobascillus are:

 -          sour mash method: the brewer leaves the mash over several days to sour before lautering and then boiling when the desired level of sourness is achieved.

 -          Souring after lautering: the brewer leaves the lautered wort to sour and then boiling once the desired level of sourness is achieved.

Pediococcus acidilactici (formerly classified as damnosus) – bacteria

Normal Habitat:

-          Plant material, fruits/vegetables


 -          Maltose, sucrose, glucose


 -          Cannot reduce nitrate

-          Will not grow in the presence of NaCl at 4%

-          Cannot grow above 35 C

-          Cannot grow at pH 8

-          Do not grow well in the presence of oxygen

Producing ideal conditions

 -          Protein rest for unmodified malts to produce free amino nitrogen

-          Avoid overly salty water (generally a good idea anyway)

-          Reduce temperatures if cultivating lactobacillus once they have finished

-          Avoid oxygenating the wort after fermentation


-          Use Pediococcus to reduce oxygen contamination after fermentation. It will form a pellicle after other organisms have diminished that protects the wort from becoming contaminated with Acetobacter.


Acetobacter aceti - bacteria

Normal Habitat:



 -          most sugars

-          needs oxygen

-          optimum pH of 5.4-6.3, but survives and grows well below 5

-          extremely alcohol tolerant

 Producing ideal conditions (only if you want malt vinegar):

 -          expose continually to oxygen

-          keep pH low

-          keep between 25-30C


-          Because Acetobacter is ubiquitous, the most common concern is keeping it out. Keeping out oxygen with Pediococcus or by keeping CO2 production going through fermentation or by purging equipment and bottles with CO2 will minimize the risk of oxygen contaminating the final product and turning to vinegar.