Directly adding lactic acid may get you a sour beer quickly, but a single note of lactic bite won’t offer much nuance. Fortunately, you can get more character by kettle souring or sour mashing without much additional effort. Some online sources confuse the two, but they are distinctly different processes even though they share the goal of letting Lactobacillus chomp through some of the sugars to generate tangy goodness.
Kettle or Mash?
When it comes to making quick sours, both approaches support brewing anything from a light tang of tartness to a quite assertive sourness. It’s all a question of how much Lacto is present and how much time it’s given to work.
The two differ on when the bacteria is brought into play. Kettle souring lets the Lacto loose on the wort, either starting with an extract recipe or after the mash. Sour mashing introduces the bacteria during the mash itself. In many respects, it’s more predictable to sour in the kettle: the mash is already complete, it’s easier to take a sample while minimizing exposure to the air and other bacteria, and you can taste the degree of sourness directly. Also, because the heat capacity of wort is higher than a mash, kettle souring should have easier time maintaining temperature.