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Microbes and Beer

Saccharomyces is commonly referred to as ‘brewers yeast’ and is used by brewers to ferment their wort into beer – so it plays a pretty important role in the brewing process! However, there are other microbes available to brewers which can create complex and interesting beer styles.

These microbes include;


Whilst there are over a dozen recognised species of saccharomyces, S. Cerevisiae has been researched the most. Known as brewers yeast, through a history of selection and breeding this strain has become ideally suited for consuming sugar and producing alcohol (as well as other desirable flavours).

We’ve had several blogs on brewers yeast and how to keep it happy in clean fermentations. It also plays an important role in mixed fermentations, providing some flavour complexity that you wouldn’t achieve fermenting with brettanomyces alone.


Brettanomyces means ‘the British brewing fungus’ and was originally introduced to breweries through wooden fermenters that were common. Brett is a widely used wild yeast for creating sour beers. Though we call Brettanomyces a ‘wild yeast’, many commonly used strains have gone through just as much of a selection process as saccharomyces. True ‘wild’ Brettanomyces strains are often unable to fully ferment wort alone.

Brettanomyces is able to ferment long chain sugar molecules (dextrins) which Saccharomyces is unable to break down, meaning a wort with Brettanomyces present will normally reach a much lower final gravity than the same wort fermented with just Saccharomyces. As Brettanomyces ferments it can produce flavours ranging from pineapple and pear, through the signature flavours of catty and horse blanket and right through to undesirable flavours such as acrid smoke or even fecal.

Brettanomyces is slower to reproduce than Saccharomyces but is able to absorb nutrients from dead Saccharomyces cells and also convert acids into esters so a prolonged maturation is often employed when using Brettanomyces in a mixed fermentation. Aging for 6 months plus is common. At this stage Brettanomyces will be the primary yeast strain so if you are bottle conditioning your beer be aware that conditioning could take several months. You may choose to re-yeast though this can be tricky to get right.


Unlike Saccharomyces and Brettanomyces which are both yeasts, Lactobacillus is a bacteria utilised in the production of many fermented foods such as yoghurt or sourdough. Lactobacillus produces lactic acid in beer, which is responsible for tart sourness but is easily inhibited by IBU’s which is why lactobacillus is the primary souring microbe in low IBU beer such as Berliner Weisse.

Lacto can be a delicate microbe, requiring a well controlled environment in order to provide the desired effect, it also doesn’t compete well with other microbes so if you wish to have lacto character in a mixed fermentation beer it is often best to pitch the lacto first, before pitching the rest of your microbes. This delicate nature is part of the reason Lactobacillus has become so popular for fast souring with techniques such as mash or kettle-souring.


Closely related to Lactobacillus, Pediococcus is also a lactic acid producing microbe. The souring, pH lowering effect of Pediococcus is much slower than that of Lactobacillus which is why it is popular in mixed fermentations – it allows the initial yeast strain to carry out fermentation before the pH drops to a level that is toxic for the yeast. Pediococcus is also able to withstand higher hopping levels and higher alcohol levels than Lactobacillus.

Many strains of Pediococcus will produce higher levels of diacetyl than the flavour threshold and unlike saccharomyces, it will not clean up this off flavour by itself. Some strains will also become ‘ropy’ which turns a beer slimy and thick, which looks very unappealing. Luckily, Brettanoyces is able to clear up the diacetyl and also break down this ‘ropy’-ness which is why Pediococcus is most commonly used in a mixed fermentation with Brettanomyces.

These are some of the more common yeast and bacteria that brewers use – which have you tried? What was your experience with them? Let us know in the comments section below or by emailing [email protected]

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