Asia Brewers Network

Bacteria selection for your kettle soured beers


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Over the last Decade, Sour Beer styles have seen significant growth in popularity.

The style emerged from traditional and niche breweries across Europe and gained global exposure through uptake in the USA, to now be featured amongst the majority of modern craft beer product lines.

Spontaneous fermentation with subsequent blending demands investment and technical skills, especially if you are using barrel Flora.

Because beer consistency and quality is so important to keep the consumer coming back for more, adoption of these time and capital intensive production techniques has become a common roadblock for brewers.

A simple process to produce sour beer

Kettle souring is a relatively modern technique, providing a fast, simple and highly effective process for brewers to produce sour beer.

With little barriers to market, this technique has developed rapidly in the beer industry globally, becoming the most popular method in practice to acidify wort which will be subsequently fermented into beer.

The Kettle souring process begins with sterilisation, then cooling of a non-hopped wort stream. It is essential to avoid adding hops pre-acidification, as iso-alpha acids derived from hop alpha acids would inhibit the bacteria’s growth and metabolism throughout the subsequent acidification process.

Once temperature reaches ideal target for bacterial growth, the bacteria is then pitched and the wort is held for 24-36 hours at constant temperature.

Completion of the process involves boiling the now acidified wort for traditional reasons, including the addition of hops (that will no longer impinge on the bacteria), and then follow the usual brew path to fermenter for the yeast fermentation. The diversion of wort through this process is shown in the below process map via the dotted path.

Illustration of the brewing and kettle souring process

Bacteria ideal for kettle souring

The passion within Fermentis to provide simple, yet elegant solutions for brewers to create consistently excellent beer, has driven them to develop two unique bacteria, SafSour™ LP 652 and SafSour™ LB 1, each offering different characters and organoleptic profiles, ideal to be used in this kettle souring process. Find out about them HERE.

At Fermentis we recognize that the lactic acid bacteria selected for your kettle souring has a profound impact on the flavour profile of your final beer. Different strains of lactic acid bacteria produce different levels of lactic and/or acetic acids which can be steered by the brewer through process management to varying degrees.

The aspiration is to achieve the equilibrium that is desired to complement all elements of the final beer.

The graph below shows the choice of bacteria can certainly affect acetic acid quantity and the brewer can play with oxygenation to achieve quite acid profiles. NB: code Lb1 refers to Fermentis Product SafSour™ LB 1 and code Lp652 refers to Fermentis Product SafSour™ LP 652.

Fermentis yeast organic acid production chart

A multitude of tools are available to the brewer to control this, firstly through the choice of your bacteria; be it homofermentative or heterofermentative, and the specific strain within these subsets.

Different bacteria can reveal a variety of aromatic profiles, they can add fruity, tropical and citrus characters, or they can be neutral, thereby respecting the aromatic signature of the yeast to be used in the main alcoholic fermentation following the kettle souring.

Secondly through the kettle-souring conditions employed, such as pitch rate, temperature, oxygenation or even pre-acidification and sugar composition. Kettle-souring conditions like temperature and pitch rate play an important part in speed of lactic or acetic fermentation time as well as the final pH reached.

The importance of pH

Brewers can adjust these to achieve their pH and flavour profile goals.

When using heterofermentative bacteria, the use of aerobic conditions will play an essential role in determining the ratio of lactic to acetic acids. It is also important to understand the subtleties of pH as opposed to total acidity.

The image below shows a comparison of the same two products: Fermentis SafSour™ LP 652 and Fermentis SafSour™ LB 1 at different pitch rates and the final pH levels.

Fermentis bacteria acidification kinetics chart


Fermentis confirms these data by undertaking repeated organoleptic analysis of trials via their expert sensory panel. The 40 strong internal panellists from different sectors of the Lesaffre Group train weekly across over 45 relevant unique attributes.

The result is a common voice that accurately detects and describes the organoleptic subtleties that the various strains of yeast and bacteria impart in beer.

The choice of bacteria offered by Fermentis, paired with the technical understanding of their behaviour in different fermentation conditions, provides brewers a wide range of delicious souring possibilities.

Find out more

If you would like to learn more about making the Sour Beer of your dreams, that your customers will adore, watch our fermentation experts and technical sales team at the “Ask Fermentis – Sour Ales” webinar with Asia Brewers Network.

Article by:

Fermentis by Lesaffre

Fermentis by Lesaffre

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