Fermentation Series: The Art of the Cold

Yeasts To Use
For Brewing Lager

"A master-level expansion on the genetics of Saccharomyces pastorianus, the discipline of patience, and the physics of refinement."

The Discipline of Patience

Brewing a world-class lager is a journey of precision. Unlike the expressive, ester-driven world of Ales, Lagers are a study in restraint. Every decision, from the mineral balance of the water to the pitch rate of the yeast, is designed to create a liquid of unparalleled clarity and crispness.

It requires a deep respect for the unique needs of your yeast and a mastery of thermal kinetics. By understanding the science behind the strains and the four phases of fermentation, you are not just brewing—you are crafting a masterpiece where there is nowhere for off-flavors to hide.

Genetic Architecture

The Hybrid Vigor of Saccharomyces Pastorianus

The Melibiose Advantage Cryotolerance

Lager yeast is a natural hybrid of S. cerevisiae and S. eubayanus. This genetic fusion allows it to ferment melibiose—a sugar that ale yeast cannot touch. More importantly, its cryotolerance allows for efficient metabolism at temperatures where other yeast enter dormancy (48-55°F). This slow, cold process prevents the production of fruity esters, leading to the signature neutral, clean finish of the style.

⚖️ Pitching Rate Kinetics

Because lagers are fermented cold, yeast metabolism is slower. To prevent a 'Lag Phase' where bacteria can take hold, you must pitch double the yeast of an ale. Professional standard: 1.5 million cells / ml / °Plato. For a 1.050 wort, this means roughly 375 billion cells.

🧪 VDK Precursor Management

Yeast produces alpha-acetolactate, which oxidizes into Diacetyl (buttery flavor). In the clean environment of a lager, even 0.1ppm is detectable. Managing these Vicinal Diketones (VDKs) through temperature manipulation is the hallmark of a master brewer.

The Essential Strains

Quantitative Profiles of Lager Yeast

Weihenstephan, Germany

W-34/70 (Saflager W-34/70)

Profile: Exceptionally clean, crisp, and malty. Allows malt and hop character to shine through with a neutral flavor profile.

Best For: Everything. German Pilsners, Helles, Bocks, Oktoberfests. This is the ultimate all-rounder.

"Arguably the most legendary lager yeast in the world. It offers exceptional attenuation (80%+) and a very high flocculation rate."

VLB-Berlin

Safale S-23

Profile: Produces slightly more fruity esters than W-34/70, especially when fermented at the higher end of its range. Finishes very dry.

Best For: Fruity lagers, Dortmunder Export, and American-style Pilsners.

"This 'fruitiness' is actually a traditional hallmark of many Dortmunder styles, providing a rounder mouthfeel and subtle aromatic complexity."

Hürlimann, Switzerland

Saflager S-189

Profile: A very neutral fermenter that enhances maltiness and body. Low sulfur production.

Best For: Traditional European lagers where a rich, malty character is desired, like Bocks and Dunkels.

"Produces exceptionally low levels of sulfur compared to German strains, making it easier to sample and monitor throughout fermentation."

From Pitch to Pour

The Four Critical Phases of Fermentation

01

Oxygenation & Pitching

Oxygenate your chilled wort thoroughly before pitching; yeast requires sterols and fatty acids produced via oxygen exposure for a healthy growth phase in high-stress, low-temp environments.
02

Primary Fermentation

Pitch into wort chilled to 48-55°F (9-13°C). Maintain this temperature steadily for 1-2 weeks. This is the 'Clean Phase'—the cold suppresses ester production.
03

The Diacetyl Rest

The Pro Move. As fermentation hits 75% completion, allow the temp to rise to 60-65°F (15-18°C) for 2-3 days. This encourages the yeast to re-absorb alpha-acetolactate, chemically reducing diacetyl into acetoin (neutral flavor).
04

Lagering (Cold Storage)

Lower the temp by 2-5°F each day until you reach 32-38°F (0-3°C). This phase is a physical and chemical polishing. Sulfur dissipates, yeast flocs out, and polyphenols precipitate with proteins (cold-break).

Sulfur & DMS

Managing Volatile Off-Flavors

Lager ferments often produce high levels of Hydrogen Sulfide (H2S), smelling like matches or rotten eggs. This is actually normal. The 'Lagering' phase allows these sulfur compounds to volatilize and blow off. Similarly, DMS (cooked corn) is a constant threat with lightly kilned Pilsner malts.

Sulfur Scrubbing

"During lagering, the slow release of residual CO2 acts as a 'gas lift,' physically carrying sulfur molecules out of the liquid."

DMS Management

"Boiling volatilizes SMM into DMS. Rapid cooling is then required to stop SMM from continuing to convert into DMS once the boil has ended."

The Ion-Malt Equilibrium

Engineering the Palate with Water

Bicarbonate & pH Buffering

Lager brewing, particularly pale styles like Helles and Pilsner, requires soft water. High residual alkalinity (bicarbonate) fights the natural acidity of the malt, pushing the mash pH too high (>5.6). This extracts harsh polyphenols from the grain husks. Master brewers often use RO water and add specific amounts of Calcium Chloride to ensure a mash pH of 5.2, yielding a 'softer' malt profile.