Kettle souring has become extremely popular with homebrewers in recent times. As sour beers grow in popularity brewers are looking for a way to create the complex, sharp, tart and drinkable styles that many people love without having to wait months or even years for the results.
Some brewers may opt to achieve this via a sour mash, which involves mashing as normal and then inoculating the mash with lactobacillus and keeping this warm. Similar to kettle souring, this method means that lactobacillus (or any other bacteria) will be killed off when you boil your wort but many brewers agree that this method gives you the least control over the process and is most prone to producing off flavours.
Kettle souring on the other hand gives you a bit more control over the process and gives you a few options (such as allowing the lactobacillus to continue on during fermentation or to keep the profile you develop during the souring period).
So what are the best practices for kettle souring?
Firstly you should decide whether or not you want Lactobacillus to enter your fermenter (where it will continue to act on the beer). If you decide that you do not then you will be performing your full boil only after you have inoculated your lactobacillus.
If this is the case, mash and sparge as you normally would and then perform a short boil of around 15 minutes. Some brewers will miss this short boil, instead choosing to raise the temperature of their mash out slightly in order to sanitise the wort but as this great article from the sour beer blog states, this is often not enough to sanitise the wort and can lead to issues further down the process.
Once you have boiled, cool your wort to 47°C (116.6°F) and use food grade lactic acid to adjust your wort pH to 4.5 (you will find that post boil your pH will likely be between 5.0 – 5.3). Lowering the pH has the dual purpose of helping with head retention and better protecting the wort from contamination.
Once at your desired pH level, pitch your lactobacillus strain or add a hop sock of uncrushed base malt (such as Pilsner or Wheat), which naturally harbours lactobacillus. If you have the capability you should then blanket your wort with CO2 to make it anaerobic (oxygen in the environment introduces unwanted elements and inhibits the correct growth of the right bacteria) before putting the lid on your Grainfather and wrapping it tightly in cling film (saran wrap or glad wrap).
Check the pH of your wort daily, making sure you keep everything as sanitary as possible. For a Berliner Weisse or Gose (two popular styles for this method of souring) you are looking for a pH of between 3.3 and 3.8. When you reach this level you can then perform a full length boil, adding any hops that you wish (though for a Berliner Weisse consider keeping this to a low level of bittering hops).
|Full length boil|
After the boil, attach your counter flow wort chiller as usual and chill directly into your fermenter, pitching your desired strain. If you’re making a Berliner Weisse, consider using a clean and neutral yeast and if your pH is lower than 3.5 you should consider upping your pitching rate!
For anyone who wants to carry the lactobacillus through to fermentation, do your full length boil as usual, after your mash and sparge but only bitter to between 3 and 5 IBU. Lactobacillus is extremely sensitive to hops so high IBU is something to avoid. If you’re planning a ‘hoppy sour’ then you should consider following the method for boiling after souring.
Cool your wort to around 47°C (116.6°F) post boil and adjust the pH to 4.5 before pitching your lactobacillus strain. Again, place the lid on the unit and wrap well, taking regular pH samples until your pH is within the 3.3-3.8 range (or tastes as sour as you would like). Limit oxygen exposure as much as possible at this stage. Once your beer is at the desired level of sourness, transfer to your fermenter and pitch your yeast.
Sour beers are one of the fastest growing styles in craft beer but the production of good craft beers requires attention to detail, patience and a strict adherence to best practices. Even for ‘quick’ methods such as kettle souring, it is important to follow the steps correctly to create a great beer.
Clayton Morrison (who designed the Anzac Ale recipe from last week) was kind enough to share his great recipe for a kettle soured Berliner Weisse;
2kgs Ale Malt, mashed at 65°C (149°F) for 60 minutes. Sparge as normal.
Sour as per above, then commence a 10 minute boil and use 5g (0.2 oz) of C Saaz for 10 minutes at start of boil. Cool and pitch Mangrove Jack’s M44 US West Coast yeast. Ferment until Terminal Gravity is reached and keg/bottle as usual.