Somewhere, at some point in history, a Bavarian brewer made a decision that would change the drinking habits of the entire planet. He looked at his beer, looked at a cold cave, and thought - "I am going to put that in there and wait several months to see what happens."
This was either an act of extraordinary genius or spectacular procrastination. Possibly both. Either way, the result was lager - the most consumed style of beer on Earth, and the one that most people drink without ever once wondering how it actually gets made.
That ends today.
To understand lagering, you first need to understand that there are broadly two families of beer yeast, and they behave quite differently.
Ale yeast (Saccharomyces cerevisiae) is the sociable, enthusiastic type. It ferments at warmer temperatures - typically between 15 and 24 degrees Celsius - works quickly, and produces a range of fruity, complex flavour compounds as it goes about its business. Ales have been brewed this way for thousands of years.
Lager yeast (Saccharomyces pastorianus) is a different creature entirely. It prefers cold temperatures, typically between 1 and 10 degrees Celsius, works slowly, and produces a notably cleaner, crisper flavour profile with far fewer of the fruity esters that characterise ale. It also, crucially, settles to the bottom of the fermentation vessel when it is done - which is why lager yeast is often called a bottom-fermenting yeast.
This bottom-fermenting behaviour was first documented in Bavaria in the 15th century, where brewers noticed that beers stored in cold Alpine caves during winter came out dramatically cleaner and more stable than beers fermented at room temperature.
They did not fully understand why. They just knew it worked. And so they kept doing it.
The word "lager" comes from the German lagern, which simply means "to store." And that, in its most straightforward form, is exactly what lagering is - the process of storing beer at near-freezing temperatures for an extended period after fermentation is complete.
This cold conditioning phase - which can last anywhere from a few weeks to several months - is where the magic happens.
During lagering, a number of important things occur:
"Lagering is essentially the beer equivalent of letting a good roast rest before you carve it. Skip that step and you will know immediately that something is wrong, even if you cannot quite explain why."
This is the part that tends to alarm people who are accustomed to the pace of modern life. Traditional lagering takes time - real, honest, unhurried time.
A classic German lager, properly made, might spend four to six weeks in primary cold fermentation, followed by another four to twelve weeks in a conditioning tank at temperatures close to freezing. Some traditional bock and doppelbock styles are conditioned for the better part of six months.
This is not inefficiency. This is precision. The slow, cold environment gives the yeast time to do its cleanup work methodically - reabsorbing off-flavours, clarifying the beer, and allowing the carbonation to integrate properly. Rush any part of this process and the beer will tell you.
It also, historically, made lager brewing a seasonal and logistically complex endeavour. Before refrigeration existed, Bavarian brewers could only lager beer naturally during winter, storing it in caves packed with ice cut from frozen lakes - which is partly why traditional Bavarian breweries were built into hillsides and why the word "cellar" features so heavily in lager brewing culture to this day.
Mechanical refrigeration, which became available to commercial breweries in the latter half of the 19th century, transformed lager production entirely. Suddenly, any brewery anywhere in the world could produce cold-conditioned beer year-round.
This technological leap is, in no small part, responsible for the global dominance of lager as a style. By the early 20th century, crisp, pale, cold-conditioned lagers had spread from Central Europe across the entire world.
"Give a brewer refrigeration and six months, and they will give you something worth drinking. Give a large corporation refrigeration and a tight quarterly deadline and... well. That is a different conversation."
Modern craft brewers have brought renewed respect and rigour to the lagering process. Across the world, small breweries are now producing traditionally lagered pilsners, helles, dunkels, bocks, and märzens - beers conditioned the old-fashioned way, for the proper amount of time, with results that are genuinely worth seeking out.
When you are holding a well-made lager, you should be experiencing:
Next time you pick up a cold lager, spare a small thought for the Bavarian brewer who first shoved his beer into a cave and waited patiently to see what emerged. He had no idea what he was doing, scientifically speaking.
He was, however, absolutely right.