So this week, Beer Cache is brewing a Marzen.

Märzenbier is the beer style that is served at Oktoberfest in Germany. It’s usually begun in March (hence the name) and cold fermented – lagered – all summer, traditionally in ice-packed caves.

But it’s not just the chilly temperatures and lengthier fermentation that makes your lager (like a pilsner or a Marzen) a different branch of beer from an ale (such as a scotch or a pale ale).

In conjunction with the cold fermentation, what really makes your lager a lager is the species of yeast that you add.

Lager Yeast

Lager yeast is a recent discovery – 1883, to be exact – that revolutionized brewing the world over.

Part of what made this yeast so different from what had been used for centuries prior was that it had the necessary enzymes to consume two extra sugars compared to ale yeast.

(For the beer geeks out there, these malt sugars are raffinose and melibiose.)

This extra sugar consumption results in a drier-tasting beer; less of that residual sweetness that you would get in the finish of, say, a red ale.

Cold Fermentation

Lager yeasts are Yukoners at heart, thriving in cold temperatures.

Lager yeasts excel between 7-12C, and during long-term storage (literally the definition of lagering) the temperature is held between 0-4C.

(Comparatively, ale yeasts do their best work between 15-24C … you won’t see many ale yeasts coming up for Rendezvous.)

What Lagering Doesn’t Do

Lagering doesn’t make the beer light in colour. That is the result of the grains used to make the beer, and nothing to do with cold fermentation or lager yeast.

The grain bills for most commercial lagers are light simply because the mass market likes a light coloured lager.

However, you absolutely could brew a lager as black as a Guinness, and you can find many craft and microbreweries that do.

Lagering doesn’t make your beer really fizzy. Fizziness – or carbonation – is determined by the brewer or manufacturer, and can be as high or low as they wish.

While a lot of light coloured lagers are very carbonated, that’s just a choice made by the producers and isn’t a feature of the lager yeast or the lagering process.

Lagering doesn’t make your beer crystal clear. If you treat your yeast right, the process of lagering will help produce a clear beer, as the cold temperatures prompt the yeast to settle to the bottom after they’re finished fermentation.

The yeast itself helps to create a clear beer by having efficient settling properties (flocculation) which gets it out of suspension, equalling a clearer beer.

But really, almost all lagers that you buy, save craft ones, have been filtered to ensure further clarity.

So usually, with a crystal clear lager, you are seeing the result of filtration, not lagering … or the chunks of ice that you are probably seeing on the ad.

So What the Heck Does Lagering Actually Do?

Lager fermentations are slower than ale ones and, in taking their time, they become perfectionists.

The yeast give off fewer flavour by-products, so the focus of the beer is on the malt and hop flavours, and the yeast profile doesn’t interfere.

The yeast by-products that ale fermentations create are hallmarks of ales: they’re deliciously complex.

Lagered beers, comparatively, are ‘cleaner’ tasting: purposely less complex and pointedly more refined.

These key differences – the type of yeast, the temperature it enjoys, and the flavours it does (and doesn’t) provide – are what give lagered beers their signature profiles. Crisper, cleaner, drier and fewer fruity notes.

In homebrewing, it’s often said that brewers make wort and yeast makes beer.

We’re off to make some Marzen wort, and we’ll leave the making of the beer to our lager yeast.

Please enjoy this article responsibly.