What is Sour Beer and how is it made Sour?

Unbelievably, sour beer is for the most part still the same as the beers you’re drinking on a day to day basis. The beer starts the same way, using the four main key ingredients that are used to make regular Lagers and Ales which are water, hops, malt, and yeast. The difference comes in the flavour profile which, as the name suggests is sour. This is achieved by a slightly alternative form of fermentation due to the adding of souring bacteria, namely Lactobacillus or Pediococcus, both of which are lactic acid producing bacteria. The pH level drops through the fermentation which is what causes the taste perception to be triggered and recognised as “sour”.

Basic styles of Sour Beer.

Over the centuries that soured beers have been produced a large variety have been developed. Most popular today are Lambic and Gueuze, traditionally produced in Belgium and the Flanders Red and Brown Ales which are also produced traditionally in Belgium. Moving across Europe a couple of other very popular styles include Berliner Weisse and Gose which were produced in Germany.

More recently we have seen the Wild Ales come onto the scene which take a lot of inspiration from that of the traditional Lambic though not all of it is fermented in a Koelschip (coolship), and even more recently is a style which is being called a Kettle Sour.

Lambic is traditionally produced in the Pajottenland of Belgium and the Brussels region by the well-known, Brasserie-Brouwerij Cantillon. It is an open fermented beer which comprises of 60-70% malted barley and 30-40% of unmalted wheat and a turbid mash is performed. After the extensive brew-day which takes far longer than the usual brew most styles require it is transferred to a Koelschip where it cools and spontaneous fermentation can take place. As the wort cools due to the cool nights breeze the wild microbes and drawn in and land in the wort, inoculating it with a huge number of different microbes. Today we recognise the main microbes in Lambic are Saccharomyces Cerevisiae, Saccharomyces Pastorianus, Brettanomyces and the souring agent Pediococcus. The beer is then transferred to a variety of different oak barrels sourced from places around Europe and aged for up to 2-3 years. Gueuze is a coming together of Lambic that has been aged for typically 1, 2 and 3 years and blended to taste according to the brewer/blender.

Koelschip in Belgian Sour Brewery

Flanders Red and Brown Ales are most notably produced by Brouwerij Rodenbach, located in Roeselare, Belgium. Until the 1970s, the beer produced by Rodenbach was spontaneously fermented. Now it is produced by a mixed culture of already existing microbes that are within the brewery. A noticeable difference between the sour beers produced in the style of Flanders Ales are that they have both a lactic acid presence as well as an acetic acid presence. Unlike that of Lambic, the beer produced in this region uses Lactobacillus which helps provide quite a sharp acidity and character to the finished product and acetic acid is promoted to an extent which brings a slight vinegar character to the beer. The beer as the style of the name suggests is also a darker colour than that of Lambic. This is achieved by a more complex grain profile which will consist partially of a longer kilned malt helping to provide the colour. These beers are then aged in large oak barrels or Foudres which are an extremely large oak tank.

The Berliner Weisse style of beer is a beer which uses a large amount of wheat creating a cloudy appearance, along with lactic acid producing bacteria, Lactobacillus. The style is typically quite low in ABV and relatively light in body and is traditionally produced in Northern Germany. The wort is usually produced with a wheat content between 25-50% and the addition of souring bacteria is used either in the primary fermentation or by secondary within the bottle of the final product. A style not to dissimilar from the Berliner Weisse is the Gose. This beer is produced using both salt and coriander and traditionally was spontaneously fermented giving it a unique character as the Lactobacillus and Brettanomyces would be present for the entirety of fermentation. Nowadays the majority of breweries producing both the Berliner Weisse and Gose are using a process called “Kettle Souring”.

A Kettle sour beer means to pre-acidify the wort before primary fermentation takes place. This is done in a wide range of ways, including inoculation with a pure strain of Lactobacillus, using yogurts or even probiotic tablets. Once the target acidity level has been achieved the beer is boiled to kill off the bacteria and allow the acidity level to remain constant from the start of fermentation until when it is consumed.  The evolution of Kettle Soured beers has meant that we now see beers ranging from pale golden colours to that of a dark rich black, beers which are 3% ABV all the way to 12% or possibly higher in some cases and even the unlikely relationship where beers are being called Sour IPAs. This is made possible by the pre-acidifying of wort and the bacteria not being inhibited by the hops which are added in the boil. This is also a great way to make sour beer for those wanting a finished sour product to drink and don’t have time to age the beer for an extended period.

The last remaining style that is being seen a lot today in the brewing of sour beer is the Wild Ale. This style of beer is a little up in the air depending on who you talk to. The word “wild” to many means that the beer has been fermented with completely wild microbes sourced from a non-cultured source. To others it means microbes that are from the wild, whether they’re captured via spontaneous fermentation or via a yeast lab that has previously captured and now colonised. Wild Ales are typically aged anywhere from 3 months to 12 months and are soured using both Lactobacillus, Pedioccocus and are fermented with Brettanomyces. This does not suggest that these beers can only be fermenter using this select yeasts and bacterias. There really are no style guidelines for a Wild Ale which appeals to many people and allows great creativity. Wild Ales will vary from a standard 4% ABV and can range up to 13% ABV though most are usually found around 6% ABV. Many are aged in Stainless Steel tanks whilst others are aged in a variety of different vessels, whether made from oak, concrete, or clay.

Making a Sour Beer.

It does not have to be a complex process to make a sour beer, however it is recommended that you can first brew a well-made clean beer.

The easiest way to create a sour beer is to use the kettle souring method. Start the brew day like you would any other brew day, mash in at a temperature that you have had success previous, for example 64 Celsius. Once the starches have been converted to sugar you can transfer to either your boil kettle, or another vessel for pre-acidifying. Depending on the cell count and how aggressive the strain or strains of Lactobacillus are you’re using will depend on how long it takes to achieve the desired pH level. Once the acidity level is reached, transfer back to the boil kettle, or if the wort is already in the kettle you can fire up the heating elements or the burner and bring it to a boil. After this boil, you can choose to ferment the wort with a variety of different yeasts. A good way to start is by using a clean ale strain that is relatively acid tolerant. US-05 is fantastic for this and will produce a very clean tasting beer without being affected by the acid level.

Some tips for Kettle Souring

  • There is speculation on whether Oxygen plays a negative role in production of off flavours, specifically Isovaleric Acid or Butyric Acid (vomit, off cheese etc). By transferring to another vessel, you may be able to inhibit oxygen intake and purge with CO2. It has become common practice in the homebrewing community to use ball lock kegs for this.
  • Use an acid tolerant yeast. As mentioned earlier, US-05 is a great yeast to use as it produces extremely clean flavours and is acid tolerant. Many Brettanomyces cultures are also acid tolerant and will give a more authentic sour beer character. Some yeasts such as a Belgian Wit or even some of the English Ale strains have been found to be less acid tolerant and can cause a halt in fermentation or fail to begin fermenting at all.
  • If you’re choosing to use Probiotics to sour with, make sure to read the ingredients as some do contain cultures that won’t benefit your final product at all and cause spoilage resulting in having to throw the batch away.

Mixed Culture / Wild Ale Souring.

This method is slightly more tedious and will test your patience and brewing skills. Again, we begin with creating a beer using your normal method of mashing in and eventually boiling. There are some more techniques that can be employed here such as different mash profiles, however this is not necessary and a simple Saccharification Rest will do just fine. If you’re looking for the beer to sour more quickly you will want to lower the hop rate in the boil, or if you have time and you’re wanting a more complex, slower aged beer you can use a slightly higher hop rate.

Making the beer sour whilst achieving a nice complexity a great starting point is to choose a Saccharomyces strain, a Brettanomyces strain and a bacteria strain such as Lactobacillus Delbrueckii or Brevis. You will notice fermentation will begin as per normal with the Saccharomyces strain doing the bulk of the fermentation, and as the fermentation continues the wild yeast Brettanomyces and the souring bacteria, Lactobacillus will start to impact on the flavour and character of the beer. The souring of the beer will likely begin after about 30 – 45 days. This period will also change depending on the temperature at which you’re fermenting. The lower the temperature the less sour or the longer souring will take. The higher the temperature the more acidity will be created and the shorter it will take.

Tips for Mixed Culture Fermentation

  • Using a new batch of Lactobacillus make sure to keep the IBU count below 5 to achieve optimal souring. If you’re looking for a longer ageing sour beer then cap the IBU at 10. It may be wise to make a starter to grow the cell count.
  • Before fermentation occurs, you can get your mash pH down to 4.9 – 5.1 and this will help to achieve head retention and stability in the finished product. It will also aid in a better overall fermentation.
  • A clean ale strain like US-05 will ferment out but not give much character itself. This will allow the Brettanomyces to express itself a little more in some instances and provide some different characters in the finished product. A Belgian strain such as Saison yeast will give some ester characters and a little spice will play off nicely alongside a Brettanomyces strain such a Bruxellensis. An English yeast strain tends to provide a slight fruit kick and works extremely well with a Brettanomyces strain such as Drei.
  • Mash hotter to achieve longer chain sugars that are only fermentable by the Brettanomyces in play during fermentation.
  • Ferment in a vessel that is glass, stainless or if plastic a non-porous plastic. Oxygen intake in any beer will eventually cause spoilage.