The Tale of Two Lagers: Technical Precision Meets the “Trojan Horse”

Brewing requires constant vigilance. On January 15th, Josh and I fired up the kettles at Cockatrice Brewery for a dual-lager session: a standard German Pilsner “Okanagan Premium Pilsner” and my “Wald Braun” Munich Dunkel. While the day started with high-precision targets, a single decision during the mash transformed one of these beers into something entirely unexpected.

The Technical Objective

We aimed for two distinct expressions of European lager traditions. The Pilsner focused on a “high fermentability” mash at 149∘F to achieve a crisp, 5.1% ABV finish. The Munich Dunkel, meanwhile, used a multi-step mash to build a complex, malty body with a deep 21 SRM color.

Style	Target OG	Target FG	Target IBU	Actual Outcome
German Pilsner	1.047	1.008	35	Clean, Crisp, Floral
Munich Dunkel	1.049	1.014	23	Accidental Oud Bruin

The “Trojan Horse” Moment

While the wort boiled, I made a critical error in judgment. I pulled a sample of my aging Plum Lambic to check its progress. At the time, it seemed like a harmless way to pass the time. In reality, opening that vessel released a “Trojan Horse” of lactic acid bacteria into the brewery air.

Fermentation Detour

We pitched WLP860 Munich Helles yeast for the Dunkel and Saflager W-34/70 for the Pilsner. Because of space constraints, we fermented both together. It took about three days to go from a “warm” 68F down to 56F (for a total of 14 days), before cold-crashing to 35F for a long lagering period. I think that short, warm window gave the stray Lactobacillus from the Lambic sample exactly what it needed to take hold in the Dunkel’s nutrient-rich wort.

The Results: A Flemish Twist in Kelowna

By late March, the difference was undeniable. The Pilsner hit its 1.008 FG perfectly, offering a clean, floral noble hop character. The Dunkel, however, finished at 1.014 with a clear, lactic tartness. It had transformed into a pseudo-Oud Bruin—unintended, but remarkably tasty.

The Mentor’s Lesson

This session teaches a hard lesson about Bio-Containment:

1. Isolate Sour Operations: Never open sour vessels on a “clean” brew day.
2. Sanitization is Not Sterilization: Standard sanitizers often fail against established biofilms or concentrated airborne bacteria.
3. Temperature Control Matters: If I had crashed the wort and fermented the WLP860 at its recommended 50∘F from the beginning, the yeast likely would have outpaced the bacteria.

While I wanted to savor a nice Munich Dunkel throughout the spring into summer, I’ll drink this “happy accident” and learn my lesson! For my next “Flex 10” batch, I’ll keep the Lambic locked away.