14:53 Jackson: Okay, we’ve talked about hops and malt and "expressive" yeast. But sours—sours feel like they’re playing a completely different game. I’ve had some that are just a little tart and refreshing, and others that smell like... well, a wet dog in a barn. What is going on there?
15:10 Lena: Welcome to the world of "Mixed Fermentation." This is where we stop using just "clean" brewer’s yeast and start inviting the "wild" side to the party. In most brewing, bacteria are the enemy—they’re what make beer go bad. But in the sour world, we use specific bacteria like *Lactobacillus* and *Pediococcus* to intentionally create acidity.
15:30 Jackson: *Lactobacillus*—isn’t that the stuff in yogurt?
2:20 Lena: Exactly! It produces lactic acid, which gives you that bright, tangy, citrusy sourness. If you’ve ever had a Gose or a Berliner Weisse, you’re tasting lactic acid. It’s refreshing, sharp, and very "clean" in its tartness. These are often made using a method called "kettle souring," where the brewer lets the bacteria do its work for a day or two before boiling the wort to kill them off. It’s a fast, controlled way to get that "pop" of acidity.
15:57 Jackson: Okay, that explains the "tangy" ones. But what about the "barnyard" ones? The "funky" ones?
16:04 Lena: That’s where things get truly wild. That "funk" usually comes from a yeast called *Brettanomyces*, or "Brett." Brett is a survivor. It works much slower than regular yeast—sometimes taking months or years—and it eats complex sugars that regular yeast can’t touch. As it works, it produces these incredibly complex aromas: leather, horse blanket, hay, or even tropical fruit like pineapple.
16:30 Jackson: "Horse blanket" doesn’t exactly sound like something I want to drink, Lena.
16:34 Lena: I know, it sounds crazy! But in the right context—like in a Belgian Lambic—it’s magical. Lambics are the ultimate "Expressive" sour. They’re "spontaneously fermented," meaning the brewer doesn’t even add yeast. They leave the unfermented beer in a wide, open vat called a "coolship" overnight, and the wild microbes from the air just fall right in.
16:54 Jackson: That sounds incredibly risky. How do they know it won’t just turn into vinegar?
16:59 Lena: It’s a huge gamble, which is why Lambics are only made in specific regions, like the Senne Valley in Belgium, where the local microflora is just right. The beer then ages in oak barrels for one, two, or even three years. Over time, the different microbes take turns. First the regular yeast, then the bacteria, then the Brett. It’s like a slow-motion relay race of flavor.
17:23 Jackson: And then they blend them, right? I’ve seen "Gueuze" on labels—that’s a blend?
6:11 Lena: Exactly. A Gueuze is a blend of one, two, and three-year-old Lambics. The young beer provides the spark and carbonation, and the old beer provides the deep, funky complexity. It’s often called the "Champagne of Beer" because it’s so effervescent and complex.
17:43 Jackson: So we have "spontaneous" sours, and we have "kettle sours." Is there anything in between?
17:50 Lena: There is "Mixed Fermentation," where the brewer *chooses* the specific microbes. Instead of just letting the air decide, they’ll pitch a cocktail of *Saccharomyces*, *Brettanomyces*, and *Lactobacillus*. This is how styles like Flanders Red Ale or Oud Bruin are made. A Flanders Red is often called "the Burgundy of Belgium" because it’s aged in oak and develops this amazing wine-like acidity and dark fruit character.
18:13 Jackson: It’s interesting how "sour" isn’t just one flavor. It’s a whole spectrum from "lemonade-tart" to "earthy-vinegar-complex."
18:23 Lena: And the GBI methodology really emphasizes that. They look at "Axis 3: Taste Balance," which separates sweetness, bitterness, and sourness. In a sour beer, the bitterness is usually kept very low because hops actually kill the "good" bacteria we want. So, instead of a balance between malt and hops, you’re looking at a balance between malt sweetness and acidity.
18:44 Jackson: I’m also thinking about the "mouthfeel" axis here. Sours often feel very "thin" or "brisk" on the tongue, right?
18:52 Lena: Often, yes, because the microbes eat so much of the sugar that there’s very little "body" left. They’re often very "dry." But some, like a Fruited Sour, add cherries or raspberries, which brings back some of that sweetness and body. A "Kriek" is a Lambic with cherries, and it’s this beautiful balance of tart, funk, and fruit.
19:11 Jackson: It feels like the more I learn, the more I realize that these "extreme" styles are just another way of exploring what ingredients can do when you push them to the limit.
19:21 Lena: That’s the perfect way to see it. Whether it’s a hop-bomb IPA or a funky Lambic, they’re all just different "maps" on the GBI Canon. And once you know how to read the map—looking at the fermentation, the sensory drivers, and the structure—the "wall of beer" at the store starts to look a lot less intimidating and a lot more like an invitation.