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W-34/70 and S-23 are the two most widely used dry lager yeasts in homebrewing, W-34/70 from Fermentis (Saflager) is the benchmark clean lager strain; S-23 from Fermentis is its fruitier, more complex sibling that polarizes opinion. I’ve fermented German lager wort splits with both to understand the difference, and the comparison is useful precisely because it illustrates two different approaches to what lager fermentation character should be.
W-34/70 vs. S-23: key specifications compared
Fermentis Saflager W-34/70: The world’s most widely used lager yeast, derived from the Weihenstephan 34/70 strain at the Technische Universität München-Weihenstephan, the most studied lager yeast in brewing science. Attenuation: 73–77% (high, produces clean, dry lager character). Flocculation: medium-high. Alcohol tolerance: up to 9% ABV. Recommended temperature range: 9–15°C (48–59°F), optimal 10–12°C. Flavor profile: very clean, crisp, textbook lager character, minimal ester, good sulfur compound management with proper diacetyl rest, the defining “clean cold fermentation” character. W-34/70 is the correct yeast for German Helles, Märzen, Munich Dunkel, German Pilsner, and any style where clean lager character is the specification. It produces a slight sulfur character during active fermentation that blows off in conditioning; finished beer is clean. Fermentis Saflager S-23: A different lager strain with distinctly different character. Origin: developed by Fermentis for a different flavor profile from W-34/70. Attenuation: 73–77% (similar to W-34/70). Flocculation: high (settles more compactly than W-34/70). Alcohol tolerance: up to 9% ABV. Recommended temperature range: 9–15°C (48–59°F). Flavor profile: slightly fruity-estery at fermentation temperatures, stone fruit, slight peach note that some homebrewers find refreshing and others find inappropriate for lager styles. The fruitiness is more pronounced at warmer fermentation temperatures (14–15°C) and minimal at colder temperatures (9–10°C). S-23 is more comparable to certain commercial European lager strains (some Czech and Central European breweries use fruitier lager strains) than to the clean Weihenstephan tradition that W-34/70 represents.
W-34/70 vs. S-23: which to use and when
Use W-34/70 when: brewing any style where clean, authentic lager character is the specification, German Helles, Märzen, Bock, Doppelbock, German Pilsner, Vienna lager, California Common, and any lager style evaluated against a German cleanliness standard. W-34/70 is the baseline lager yeast against which all others are judged, and for good reason: its clean fermentation at 10–12°C with proper cold conditioning produces textbook lager character that is correct for the broadest range of lager styles. W-34/70 also performs acceptably at warmer temperatures for “quick lager” approaches: fermenting at 14°C for 2 weeks, diacetyl rest at 17°C for 48 hours, then cold conditioning at 2–4°C for 3–4 weeks produces a beer that satisfies in the lager category. The full authentic cold fermentation (10°C primary, 6–8 week lagering at 2°C) produces noticeably better results. Use S-23 when: you specifically want slightly fruity character in a lager, certain Czech and European lager styles tolerate or welcome fruity ester notes; S-23 at 9–10°C produces a lager with subtle stone fruit character that reads as authentic in Czech Premium Pale Lager and similar styles. S-23’s higher flocculation also makes it useful when fast, compact yeast settling is needed. Some homebrewers prefer S-23 for Märzen and Oktoberfest where a slight fruity undertone complements the toasty Munich malt; others find the fruitiness out of style. Practical recommendation: If you’re new to lager brewing, start with W-34/70, it is more forgiving, more widely documented, and more broadly correct for the most lager styles. Add S-23 to your repertoire after you have a W-34/70 baseline to compare against.
Common Questions
Do I need refrigeration equipment to use W-34/70 and S-23 properly?
For the best results: yes. Both W-34/70 and S-23 perform optimally at 9–12°C, which requires active refrigeration unless you brew during winter in a cold climate. At warmer temperatures (above 15°C), both strains produce noticeably more esters and fusel alcohols, the result at 18–20°C room temperature is a beer that tastes more like an ale than a lager, defeating the purpose of using a lager strain. Options for temperature control: dedicated fermentation refrigerator (most common and most effective, a small bar fridge with an Inkbird or STC-1000 temperature controller runs 40–60°C); a wine cooler or chest freezer with a temperature controller; brewing lagers during winter months in a cold garage or basement (reliable if you live in a climate that reaches 5–12°C reliably in winter). The “no refrigeration” lager approach: use W-34/70 at its warmest acceptable temperature (14–15°C) in a cool room or cold water bath. This is feasible in autumn/spring in temperate climates and produces acceptable results. At true room temperature (18–22°C), use a kveik strain or an ale strain instead of compromising the lager strains outside their useful temperature range. Temperature control for lager fermentation is one of the higher-value equipment investments a homebrewer can make, properly temperature-controlled W-34/70 lagers are a qualitative step above almost anything achievable at room temperature.
