Brew a Spontaneous Sour Beer

While we are all stuck at home there are plenty of things we are grateful for. We also just picked up some spontaneously fermented sours. One of our absolute favorite styles of beer.

As the name suggests spontaneous sours aren’t inoculated with modern yeast or bacterial cultures. But rather they are inoculated by naturally occurring yeast and bacteria from the air. Traditionally these beers are sent from the boil kettle to a large shallow vessel called a cool ship to cool overnight. That’s where the magic happens. As the ber cools air makes contact with the surface of the beer and spontaneous fermentation happens. That may sound simple enough but successfully pulling this off requires a ton of time and attention to detail.

For more special methods of brewing beer check out our Lambic Extract Homebrewing.

The Grain bill and Mashing process

Wooden casks on top of each other in the process of spontaneous beer fermentation.

The Grain Bill

  • 55% Pilsner Malt
  • 36% Unmalted Wheat
  • 9% Pale 2 Row

For the mash schedule, we will start with a thick mash at a low temperature. And then gradually adding boiling water to raise the mash temperature throughout. For the first step we want a mash temperature of 113 F and we want it to be thick. So we are only adding enough water to cover the bottom of the grain basket.

In the next step, our target temperature is 136 F and in order to get there, we are adding boiling water to the mash. this will raise the temperature and thin the mash, Once you reach 136 F start a timer for 10 minutes.

As the third step, we pull a quarter of a gallon of wort from the mash. We also add enough boiling water to bring the temperature to 150 F. After we reach the temperature we start the times for 30 minutes. The last step is to bring it all to 185 F until the end of the mash.

The boil

Wooden beer casks left to ferment in the open space.

We are returning all of the wort back to the mash. Boil times for traditional spontaneous beers can get long. commercial breweries can change shifts and boil their wort into the small hours of the night. We aim for a 2-hour boil. This is a super small batch so evaporation will happen much faster compared to a commercial scale.

After 1 hour boil, we add our first and only hop addition which is 10 g of aged Cascade. After the boil is finished we leave the wort in the kettle and add a screen on top. We put a blood-orange peel on the screen and leave it under an apple tree in the backyard to cool overnight. The combination of these will inoculate the wort.

It’s been 12 hours and the only thing left to do is to move the wort into the carboy. Put an airlock and cross our fingers. We will put it away in our cellar at around 60 F and see what happens. Cheers.

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