Our understanding of lager brewing was acquired from German textbooks, by attending brewing school in Munich, and through dozens of visits to German breweries where we sat with brewers, drank their beer, and discussed their methods.
What did we learn? We learned that lager fermentation requires more of almost everything: more yeast, more refrigeration, more tanks, more space, more time, and more patience. Although there is a lot more we could discuss, here are some key considerations when conducting a classic lager fermentation.
Cold and Slow
Lager yeast are valued for their clean, mellow character and crispness because they produce fewer fruity esters, fusel alcohols, and spicy phenols compared to ale yeast. This mellow character is possible because lager yeast can ferment at cold temperatures that would render ale yeast inactive. Cold temperature is the key factor that slows the yeast’s metabolism, which suppresses the production of metabolic flavor by-products.
However, reduced metabolic activity also dampens the yeast’s growth rate and slows fermentation time. Consequently, lager yeast should be pitched with cell counts 50 to 100 percent higher than warm-fermented ales. Because it is costly to purchase—or difficult to propagate—large amounts of yeast, brewers often under-pitch lager yeast and compensate by starting fermentation at room temperature to stimulate yeast growth, lowering the temperature only later. Because most fermentation flavors are created at the start of fermentation, these temperatures stimulate the production of esters and other flavors. Thus, a warm lager fermentation fails to achieve the desired clean lager character.
At KC Bier, we knockout at 46°F (8°C) and pitch 1.5 million-plus yeast cells per milliliter of wort, then let the temperature free rise to 50°F (10°C) to achieve that classic lager character.
Two-Tank Fermentation and Conditioning
At the end of fermentation, yeast may have converted the fermentable wort sugars to alcohol, but their work is not done. There are still buttery diacetyl and green apple acetaldehyde to eliminate, and the yeast need to stay in contact with the beer to clean up these off-flavors. Consequently, at KC Bier we use separate tanks for fermentation and lagering. Our conical fermentors efficiently purge cold break and collect yeast for re-pitching, and our squat, dish-bottomed lager tanks provide greater surface area on which yeast can flocculate. The larger surface area puts more yeast in contact with the beer to improve their ability to clean up unwanted green-beer flavors.
Brewers frequently crash-cool ales after fermentation to shock the yeast and cause rapid flocculation, shortening production time. In our view, lager yeast should never be crashed because temperature shocks reduce their ability to clean up off-flavors. Instead, a good practice is to lower the temperature slowly after fermentation by a few degrees (2–3°F/1–2°C) per day to a final temperature of 32–35°F (0–2°C). (Lager yeast remain active at temperatures near freezing.) This practice also helps clarify the beer by precipitating tannin-protein haze, which becomes less soluble at cold temperatures.
At the end of fermentation, some lager brewers may allow the temperature to increase to 59°F (15°C) or higher to reduce diacetyl or bolster attenuation. Because the potential for yeast to produce esters is lessened after fermentation, there are few, if any, adverse flavor effects from a diacetyl rest.
Natural Carbonation
The German Purity Law, a.k.a. the famous Reinheitsgebot, allows only four ingredients: malt, hops, water, and yeast. Therefore, carbonation must be produced by fermentation; industrially produced CO2 injected into the beer would be a verboten fifth ingredient.
Because cold temperatures provide for greater solubility of CO2 at lower pressures, there are fewer obstacles for naturally carbonating lagers compared to ales. Not only is natural carbonation free of taints and cost, but it also contributes a signature lager character: sulfur. Compared to ale, lager yeast produce more sulfur dioxide, which provides a crisp, struck-match aroma common in German lagers. Cold fermentation produces more sulfur, which is retained in greater quantities by trapping CO2 from fermentation, as compared to releasing it and force carbonating with industrial CO2 after fermentation.
Other Non-Fermentation Considerations
Malt and Hops.
At KC Bier, we use 100 percent imported malt and hops from Germany, and our yeast originated from a Bavarian monastery. Location and climate affect the terroir of malt and hops. European ingredients are not better than domestic ones, but they taste different. If the goal is to produce authentic German flavor, the ingredients matter.
Mashing
We use a traditional three-temperature step mash, with at least one of the steps accomplished by decoction. We also use four different base malts. We brew pale lagers with pilsner malt, amber lagers with Vienna malt, brown lagers with Munich malt, and wheat beers with pale wheat malt. Rarely do we use caramel malt. Instead, we choose decoction to enhance the maltiness of the base malts and create a more balanced, subtle, nuanced character that embraces the essence of German brewing—balance and drinkability.
Traditional lager brewing requires “more” than a typical ale fermentation. Because the “more” requires additional costs and resources to achieve very subtle, small, and incremental enhancements to flavor, there is always the temptation to take shortcuts by buying cheaper ingredients, skipping decoction, pitching less yeast, raising the fermentation temperature, shortening the conditioning time, or using artificial carbonation.
Really, who can tell the difference if one traditional step is bypassed? And if no one will notice one skipped step, why not skip two steps? Soon the lager character has died a death from a thousand small cuts. Cutting corners is exactly why most Americans associate lager with the terms “cheap” and “tasteless.” Lager beer done right deserves respect. It’s worth it to give more.
So, lager on, lager hard! Prost!