home brewing

Creating a Sour Beer 1. Lactobacillus

Acidity in beer is produced by a range of micro-organisms. This article will briefly guide you through which are best to use on a homebrew scale to achieve similar products to those made commercially.

Lactobacillus bacteria are one of the main producers of acid in sour beers. These bacteria convert sugars into lactic acid, and a tiny amount of alcohol. Lactobacillus is traditionally used in the production of the Berlinerweisse, Gose (pronounced GOH-zuh), Lambic and Flanders Red/Oud Bruin ales. In the first two examples Lactobacillus may be added directly to freshly produced wort by throwing in a handful of fresh malted barley (as lactobacillus tends to live on grain), pure laboratory pitches or house blends. Under the correct conditions the Lactobacillus will begin to produce significant lactic acid with 24-48 hours, taking the wort from PH of around 5.2 to 3.1-3.8. Most strains of Lactobacillus are not hop tolerant, therefore very low hopping rates (i.e. <2 IBU or no hops) are typically advised at this point. The soured wort can be kept in the boil kettle during this period, and then boiled after the desired PH is reached to kill off the Lactobacillus bacteria (hops can be added at this stage if desired). This process is known as ‘kettle souring’.

Rittergute Gose LabelsThe most traditional technique for producing sour German styles such as Berlinerweisse and Gose would be to add a house blend of Lactobacillus, Saccharomyces (brewers yeast) and Brettanomyces in unison (Hübbe 2016). The natural micro-organism schedule sees Lactobacillus begin to sour the fresh wort (in the first 24 hours), quickly followed by the Saccharomyces (usually 12-24 hours) producing alcohol and C02. After around two weeks the Saccharomyces fermentation should be complete and the Brettanomyces will slowly begin to consume residual sugars and produce additional flavour complexity in your beer.

In Belgian Lambic and Flanders Red/Oud Bruin styles, Lactobacillus is typically incorporated from spontaneous fermentation, the wort having been inoculated by contact with the air (opening the windows in the brewery overnight), or by bacteria living in the barrels. As these Belgian styles are usually hopped with aged hops, Lactobacillus is usually not a major player until later on in the maturation process as it becomes acclimatised to the hop levels.



Here will follow three of the methods used for souring beer with Lactobacillus:

Kettle soured (modern) Berlinerweisse

  1. Mash beer as normal
  2. Move beer into boil kettle
  3. Bring to the boil for 60 minutes.
  4. Drop temperature to 30-40C
  5. Optional: Recommended practice is to drop the PH of kettle sours with lactic (or other) acid to 4.5 to inhibit growth of harmful bacteria prior to pitching the Lactobacillus.
  6. Pitch Lactobacillus and hold temperature at 30-40C as best as possible (or allow to drop slowly to room temperature if unable)
  7. Test PH at intervals over 24-48 hours. Once desired acidity level is reached (e.g. 3.1-3.8) bring wort back to boil.
  8. Continue brewing as if a standard beer was being brewed.


Historic Berlinerweisse

  1. Mash beer as normal
  2. Boil beer as normal.
  3. Drop temperature to 18-24C
  4. Pitch Lactobacillus (WLP672), Saccharomyces (WLP029) and Brettanomyces (WLP650).
  5. Optional (pitch Lactobacillus 24-48 hours ahead of the yeast to encourage acidity).
  6. Allow fermentation to continue for usual period.
  7. Extended aging will see additional complexity from the Brettanomyces.

Historic Lambic style

  1. Mash beer as normal
  2. Boil beer as normal except aged hops should be used.
  3. Drop temperature to 18-24C (Optional: by cooling in outside air).
  4. Optional: Add mixed yeast and bacteria culture, Lambic bottle dregs etc.
  5. Extended aging in wood will allow the greatest complexity, though well sealed glass or plastic carboys can also be used.
Lambic fermenting in barrels at Oud Beersel, Belgium.

Sources of bacteria

Lactobacillus: WLP672 Brevis, WLP677 Delbruckii or WLP630 Berlinerweisse blend (contains 672, 677 and a Weizen strain). Brewstore stock a range of strains of Brettanomyces and other yeast/bacteria blends which can also be used.

Sanitation recommendations

Additional sanitation care must be practiced with each method for various reasons. The chief reason is that you are bringing bacteria into contact with your brewing equipment and you do not want this to affect your ‘clean’ (Saccharomyces only fermented) beers.

  1. The kettle souring method should be preceded with thorough clean and sanitisation of the boil kettle including tap fittings. When kettle souring it is important to cover the wort with cling-film or lid to avoid dust/flies harbouring wild yeast and bacteria.
  2. Any equipment used for fermentation of beer using Brettanomyes, Lactobacillus and other wild yeasts should be kept separate from Saccharomyces equipment due to a risk of infection.


Hübbe, T. 2016. Effect of mixed cultures on microbiological development in Berliner Weisse. Unpublished PhD thesis.


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