The Brewer

Sour Beer Guide: Kettle Sour vs Mixed Fermentation

Sour Beer Guide: Into the Wild

For decades, “sour” meant “infected” or “bad.” Today, Sour Beer is one of the most exciting and fastest-growing segments of craft beer. But not all sours are created equal. There is a massive difference between a beer that is soured in 24 hours and one that takes 2 years.

1. The Bacteria: Lactobacillus

The star of the show isn’t yeast; it’s bacteria. Lactobacillus (the same stuff in yogurt) eats sugar and produces Lactic Acid. This acid gives the beer its tart, lemon-like acidity.

2. Method 1: Kettle Sour (Quick Sour)

This is how 95% of the “Fruit Sours” on the market are made. It is fast, clean, and controllable.

  • The Process:
    1. Mash: Make the wort as usual.
    2. Sour: Put the wort in the boil kettle. Cool it to 40°C (100°F). Pitch Lactobacillus.
    3. Wait: Let it sit for 24-48 hours. The pH drops from 5.2 to 3.2.
    4. Boil: Turn the heat back on and boil the wort. This kills the bacteria.
    5. Ferment: Cool and ferment with normal brewer’s yeast (Saccharomyces).
  • The Result: A clean, one-dimensional acidity. It is perfect as a canvas for adding massive amounts of fruit (raspberry, mango, passionfruit).
  • Styles: Florida Weisse, Fruited Gose.

3. Method 2: Mixed Fermentation (Traditional Sour)

This is the old-school, risky, and complex way.

  • The Process: The brewer pitches yeast and bacteria (Lactobacillus, Pediococcus) and wild yeast (Brettanomyces) into the fermenter or wooden barrel. They live together for months or years.
  • The Result: The bacteria create acid, but the Brettanomyces creates “funk” (leather, hay, barnyard). The flavor is layered and evolves over time.
  • Styles: Traditional Berliner Weisse, Belgian Lambic, Flanders Red.

4. Famous Styles

Berliner Weisse

  • Origin: Berlin, Germany.
  • Profile: Very low alcohol (3%), high carbonation, clean lactic sourness.
  • Service: Often served with a shot of syrup (Woodruff or Raspberry) to balance the acidity.

Gose

  • Origin: Goslar/Leipzig, Germany.
  • Profile: Similar to Berliner Weisse but brewed with Salt and Coriander.
  • Taste: Ideally, it tastes like a margarita: tart, salty, and citrusy.

5. Brewing Your First Sour

If you are a homebrewer, start with a Kettle Sour. It is safe because you kill the bacteria before it touches your plastic gear (fermenters/hoses). If you put live bacteria in your plastic fermenter, that fermenter is now a “Sour Fermenter” forever. You will never be able to brew a clean beer in it again.

Conclusion

Whether you prefer the fruit-smoothie blast of a modern Kettle Sour or the complex, funky depth of a barrel-aged Mixed Ferm, acidity adds a refreshing new dimension to beer. It is the wine drinker’s gateway into the world of grain.