Lager Yeast: Impact of Pitch Rate on Efficiency and Flavour in Cold Fermentation

For centuries, brewers in places like Germany and the Czech Republic swore by cold fermentation. They would let their lagers ferment at chilly cellar temperatures, sometimes as low as 7–9 °C. The result? Smooth, crisp, and beautifully clean beers that became the gold standard for lager around the world.

These days, most breweries ferment lagers a little warmer—usually between 10–15 °C—because it’s faster and more efficient. But recently, some brewers have been bringing back the old-school approach, inspired by Czech decoction lagers and rustic Franconian Kellerbiers. It’s led to a wave of curiosity: what happens if we take fermentation back down to 8 °C, or even colder?

Of course, brewing this way isn’t without its hurdles—and that’s where our experiment comes in.

Background and Purpose

Fermenting at such low temperatures introduces significant challenges.

• Yeast grows slowly.
• Enzymatic activity is lower.
• Risk of stuck fermentation and off-flavours (such as diacetyl) increases.

To address these issues, this experiment tested whether a higher yeast pitch rate—a relatively straightforward variable to control—could counteract the limitations of ultra-low-temperature lager fermentations.

Research Questions

1. Can increased pitch rate accelerate fermentation at 8°C?
2. How does pitch rate influence aroma formation in different lager yeast strains?
3. Is there an optimal pitch rate for balancing clean flavour with desired complexity?

Experimental Design

Four commercial lager strains were fermented at 8°C in duplicate, at three pitch rates:

• 1.0 million cells/mL/°P
• 1.5 million cells/mL/°P
• 2.0 million cells/mL/°P

Yeasts tested:

• Biergarten (Bavarian-style lager; neutral)
• Czech (traditional Czech-style lager; can be estery)
• Isar (German-style lager; can be estery)
• Premium Pils (neutral, refined lager profile)

Metrics recorded:

• Fermentation kinetics (SG drop over time)
• Aroma compound production (via GC analytical profiling)

 

Lager Yeast Fermentation Performance at 8°C

Key observations:

• Premium Pils and Biergarten showed the most variation in response to higher pitch. For Premium Pils, the lower pitch rate (1.0) produced the fastest fermentation while for Biergarten, the medium pitch rate (1.5) gave the fastest fermentation.
• Isar was notably consistent, suggesting pitch rate is less relevant for this strain in terms of kinetics.
• Czech reached terminal gravity reliably, with a less pronounced acceleration effect from higher pitch, suggesting it is well-adapted to low-temp fermentation.
• Premium Pils showed the fastest drop in SG across the lower pitch rates (1.0 and 1.5).
• Isar consistently fermented more slowly at the cold temperature.
• Pitch rate had only a modest impact on fermentation speed, and was highly strain dependent.

Conclusion: Yes, pitch rate can alter fermentation rate at 8°C, but not equally for all strains, and more yeast doesn't always result in a faster fermentation.

Aroma Development (Summary)

A detailed analysis of esters, alcohols, and off-flavour markers using headspace GC-MS (gas chromatography mass spectrometry) revealed strain- and pitch-specific patterns:

• Higher pitch rates reduced acetaldehyde and fusel alcohols, especially in Premium Pils.
• Biergarten was the most neutral and consistent across the range of pitch rates.
• Moderate pitch (1.5 M) resulted in the highest fruity ester production in Isar.
• Low pitch (1.0 M) offered the strongest floral notes in Czech via phenethyl acetate. For this strain, aroma intensity dropped as pitch rate increased.

See full aroma heatmap for profiles:

Heat map represents relative intensity of aroma compounds in this experiment (n=2). Z scores indicate how many standard deviations the measurement deviated from the mean.

We can also represent the data on a PCA biplot (think of it as a ‘flavour map'):

The PCA biplot shoes how the overall aroma profile of strains differentiates and shifts in response to pitching rate. For example, the aroma profile of Premium Pils is much more dynamic in response to pitch rate than Biergarten, where all the profiles cluster in the bottom right quadrant.

Practical Recommendations for Ultracold Fermentation

Strain	Best Case Use	Recommended Pitch Rate at 8 Celsius
Czech Lager	Fruity/floral lagers	1.0-2.0 Mcell/mL/DegP, depending on ester preference
Isar Lager	Fruity esters and mild warmth	1.0-2.0 M Mcell/mL/DegP, without much difference
Biergarten Lager	Balanced, clean profile	1.0-2.0 M Mcell/mL/DegP, without much difference
Premium Pils	Super clean, neutral lagers	1.0-1.5 M Mcell/mL/DegP

 

Final Thoughts

Brewers experimenting with low-temperature fermentations have good reason to revisit pitch rate as a key control lever. This experiment shows that:

• Fermentation can be (slightly) accelerated at 8°C with higher pitch rates, but this is strain dependent.
• Aroma expression is non-linear, and over-pitching may strip desirable character. Under-pitching can result in a higher level of esters and acetaldehyde which may not be desirable.
• Strain selection remains the most important decision. Not all yeasts can handle 8°C gracefully.
• Purchasing high pitch rates gets expensive. In order to control costs, we recommend brewers planning ultracold ferments to put their lab-generation lager yeast through a different beer first (such as a light lager or helles) in order to generate the higher cell mass recommended for ultracold fermentation. For example, you could repitch from a light lager into a traditional Czech Pilsner.

By dialling in the right combination of yeast and pitch rate, brewers can confidently produce clean, expressive, and traditional lagers — even at very low cellar temperatures.

Want more data drops like this? Sound off in the comments and let us know what we should study next.