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Beer School

Lesson 9: Lagers vs. Ales

A lager is a light, crisp and refreshing beer. It’s fairly easy to taste the difference between a lager and ale, but what sets these two apart from a brewing perspective?

The defining difference between lagers and ales is based on yeast strains, as well as length and temperature of fermentation. An ale uses a top fermenting strain of yeast called Saccharomyes cerviase and is produced at warm temperatures ranging between 18c and 23c. In a top fermenting beer, ale yeasts rise to the surface and produces beer high in esters, or fruity aromas.

Lagers, on the other hand, use a bottom fermenting yeast strain called Saccharomyces pastorianus, named for Louis Pasteur. Lagers are fermented at much cooler temperatures than ales, between 9c and 15c for primary fermentation and 4c and 5c for secondary fermentation.

Because lagers are fermented cool and conditioned cold, yeast metabolism is slowed down. Where ales are fermented for 2 to 3 weeks, lagers require between 6 and 8 weeks for fermentation. A longer fermentation time allows for chemicals to be reabsorbed and converted into more neutral compounds. Lagers should be free from noticeable esters or phenols, allowing for malt and hops to take centre stage.

A brief history of lagers:

The word lager comes from the German word lagern, meaning, “to store.” In the 19th century, prior to the advent of refrigeration, German brewers would dig cellars for cold storage or lagering, to keep beer cool during the summer months. A long storage period meant that the yeast had time to settle out, so the beer was cleaner and paler than it was prior to aging.

By the mid-19th century, lagers became hugely popular in commercial markets. This trend was fueled primarily by technology with the introduction of refrigeration. During this time, many places in Germany had banned brewing in the summer, so being able to cool beer effectively meant that it could now be brewed year round. In addition to technological advancements, the development of clean yeast strains and ability to kiln light pilsner malts, also contributed to transforming the lager trend into a worldwide phenomenon.

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