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So, you want to make a kettle sour, eh? This is truly one of my favorite styles to brew because, while the raw materials may be simple, executing this style to perfection is a challenge that requires absolute control of your process from start to finish.
For a kettle sour, pH is of obvious importance. I find it helpful to outline the various pH targets—throughout the course of the brew day, kettle-souring, and fermentation—to make sure I’m doing everything right to achieve those targets. Our pH targets are as follows:
- Mash: 5.5
- In the kettle, post-acid addition, pre-Lacto: 4.8
- Post-Lacto, pre-boil: 3.35
- Post-boil: 3.4 (pH tends to rise during a 90-minute boil)
- Post-fermentation: 3.3
Post-Lacto, we begin checking pH about eight hours after pitching, and then hourly after that if it is not ready. Usually, the pH is in range eight to 10 hours after pitching, but for certain strains, it may take up to 48 hours to complete acidification.
Besides meeting pH targets, making absolutely certain that all oxygen has been purged from the souring vessel and eliminated from the wort itself is paramount to success. Any oxygen left in solution will result in butyric aromas (rancid, cheesy, vomit) in the final product, creating a beer that does not exhibit wonderfully bright lactic and lemony aromas.