• Kelsey Picard

Lager: A story of luck in an Argentinean Oak Barrel

Rugen brau Spezial Hell pilsner, Switzerland 2017

Initially I had planned to just write a short ReBrewer Two about Boekamp’s lager but researching what makes lager yeasts unique led me down a very nerdy rabbit hole that I couldn’t get out of without writing a blog about why the world owes its favourite alcoholic beverage to genetics and pure luck.

Until discovering Boekamp Bier, lagers never really piqued my interest when reaching for beers at my local bottle store. I always associated lager with bland, watery beer like Corona, Heineken etc. Having visited Europe in 2017 I ignorantly tasted some of the best, and longest produced lagers the world has to offer, and yet it was the weissbier that I was obsessing over at the time.

Beer can be largely grouped into two categories; Ales, and lagers. All beer styles from IPAs to stouts, pilsners to sours will be in either of the two groups based how the beer was fermented by different yeasts (accessory yeasts like Brettanomyces can be classified as “wild”, however they are often used in conjunction with ale yeasts).

The scientific name for brewer’s yeast, Saccharomyces comes from the Greek words for sugar ‘saccharon’ + fungus ‘myces’, which is exactly that – a sugar fungus.

Computer generated image: Saccharomyces cerevisiae

Different strains or species of Saccharomyces are used for ales or lagers. Ales are brewed with a species called Saccharomyces cerevisiae, which has been used for thousands of years. The cerevisiae species name comes from Latin and means "of beer". Ale yeasts are top-fermented, where the yeast rises to form a layer at the top of the vessel. Lagers are bottom-fermented, which means the yeasts do their job at the bottom of the tank, and at colder temperatures. This is made possible by the special yeast used called Saccharomyces pastorianus, named after the famous French microbiologist Louis Pasteur, who is thought to be the first to prove that yeast is able to ferment sugar into alcohol (this yeast is also known as S. carlsbergensis, named by Danish Mycologist Emil Christian Hansen during his time working at the Danish brewery Carlsberg in 1883). This strain has only been used for the past few hundred years or so, with the ability of this yeast strain to sink to the bottom of the fermenter tank and grow very slowly at much cooler temperatures. This is what give lagers their distinct style.

You may have heard of Germany’s beer purity laws “Reinheitsgebot”– established in 1516 in Barvaria by the Barvarian Duke Wilhelm IV. The “Barvarian order” states that beer be made with only water, malted barley and hops. Yeast was added later upon its discovery. By 1906 this purity order was made into law for all of Germany. A later law introduced in 1553 by Wilhelm’s successor Duke Albrecht V, dictated that beer must only be brewed during the colder months between September 29 (Michaelmas) and April 23rd (Feast of St George). Unknowingly, but probably driven by taste, this rule was limiting the growth of competitive microorganisms that grow at warmer temperatures that could spoil the beer. We can thank Albrecht’s new rule for the lagers we drink today!

Figure from Gibson & Liti (2015) doi: 10.1002/yea.3033.

S. pastorianus, used for production of lager beer, the most produced alcoholic beverage worldwide is a S. cerevisiae X S. eubayanus hybrid. This spontaneous hybrid emerged by S. cerevisiae mating with another strain of yeast. This is unusual for yeasts as they normally reproduce asexually by budding. For years it was unclear where the S. pastorianus strain had originated until 2011 when a group of researchers discovered a very closely related yeast strain in Argentinean oak trees called S. eubayanus.

Genome sequencing determined that the parent yeast strain must have made its way to Europe in an Argentinean oak barrel. Somewhere in the process of aging beer in oak barrels, S. cerevisiae and S. eubayanus hybridised, and produced what we now know to be S. pastorianus.

This lager yeast yields its cold tolerance from the Argentinian strain’s mitochondria – the “Powerhouse of the cell” which enables the yeast cells to remain active at lower temperatures.

Cold brewing reduces the flavour compounds produced by yeast, so lagers typically feature light malt flavours with subtle noble hop bitterness.

Another benefit of the colder temperatures is that the yeasts live for longer in the brew. Brewers will extend the time the yeast is left in the beer at temperatures around 1°C. This period of cold is called cold-conditioning or lagering. This extended time in the beer means the yeasts “clean” up the beer, reducing the off-flavours that would normally be “off-gassed” or evaporated away at ale yeast temperatures.

Average sugar composition of total sugar in wort. Source: https://eurekabrewing.wordpress.com/2015/01/13/sugar-composition-of-wort

The other amazing thing about this hybrid is that it rescues S. eubayanus’ inability to metabolise the second most prevalent sugar in the wort, maltotriose, so S. pastorianus must have inherited this ability from S. cerevisiae. The fact that the brewing time can be extended, and the yeast remain alive and functional means that once the yeast’s favoured sugars, glucose and maltose, are consumed in the wort, they then move onto ferment maltotriose. Complete sugar utilization is desirable for lager fermentation as it optimizes alcohol content and reduces residual sweetness, producing a crisp lager.

This super-baby yeast strain is more efficient at fermenting more sugars at lower temperatures than either of its parent strains. This hybrid has also since undergone reorganization of its genome and lost chunks of S. cerevisiae genes that are presumably redundant when fermenting at lower temperatures.

Physiological differences between ale and lager strains are most probably an outcome of their considerable genetic differences too.

Image source: https://biol421.opened.ca/out-with-the-old-in-with-theold-brettanomyces-a-spontaneous-phenomenon/

Ale strains are called top-fermenting because they form a head yeast at the top of the wort during fermentation, whereas bottom-fermenting lager strains flocculate and sediment to the bottom of the fermentation tank in the late phase of fermentation. This difference has been explained by the different surface hydrophobicity (how well they mix with water) between ale and lager yeast strains. Ale strains are suggested to be more water repelling due to a higher surface protein concentration on the outside of their cells, and because of this, they are more able to adhere to CO2 bubbles and to form yeast heads at the top of the fermenter.

Boekamp have set the bar very high for good, authentic lagers brewed in Tasmania. It is not often that a craft brewery will produce both ales and lagers due to lagers taking much longer, reducing their capacity - less product, less profit. Perhaps inspired by Boekamp or just wanted to branch out, Moo Brew have released their BREW Tassie Lager ahead of MONA FOMA festival. We predict (and hope) 2021 will be the year of craft lagers in Australia.

19 views0 comments