Are you a top or a bottom? Mr Science explores ales and lagers!

Sometimes I get ahead of myself and think everyone is on board with stuff. As a brewer, drinker and a guy who is an all around beer dork, I have the expectation that people are with me on the intricacies of beer. Recently, I witnessed the terms ale and lager being used interchangeably. After I freaked out and made an intense mockery of the person in my head, I calmed down and said to myself: “Wait a sec, stop being such a dick and think rationally for a sec.” Then I said out loud: “Fuck that! Rationality is for the sober!” I had another shot of booze and talked loud for a while. When nursing the subsequent hangover, ruminating on the things that I have done wrong in my life to warrant such a sorry state, I figured that it might be prudent to discuss the differences that make an ale an ale and a lager a lager. This shit is important!

Fuck that! Rationality is for the sober!

You might think that this is more an exercise in beer styles but really, it comes back to the all important organism: YEAST! I discuss fermentative organisms here a lot, but they are really why we are all getting drunk, you know? Anyway, lagers and ales are two separate things for a few reasons, but the critical aspect is that the yeast that make these styles different evolved in and were subject to selective pressure in significantly different environments which led to the creation of different beers around them. I guess you could say that the yeast and the beers co-evolved to bring us to our modern understanding of the styles.

Saccharomyces cerevisiae rules!

Saccharomyces cerevisiae is the species of yeast that likely started the whole beer and bread culture that was the effective inception of civilization. We can consider S cerevisiae to be brewer’s yeast as well as baker’s yeast. It is a single-celled eukaryote that has the adaptation to, in high concentrations, metabolize glucose into carbon dioxide and ethanol. Since it is ubiquitous in nature, it was only a matter of time before it got into the products that were sustaining our primitive ancestry. S cerevisiaegrows like a champ in any generally warm environment and acted as the “magic” that produced beer out of any number of methods used by groups throughout the world.

Ale was the predominant style for a few thousand years of brewing. S cerevisiae ferments quickly and forms a thick layer of foamy material called kreusen on the surface of the fermenting liquid. Due to membrane hydrophobicity, the yeast is lifted by the CO2 in the beer and brought to the surface. This is why ale is considered a product of a “top-fermenting” yeast. Throughout brewing history, brewers learned that they can collect this foam and add it to the next batch to ensure vigorous fermentation. This is also the beginning of selective pressure to form consistent local characteristics related to certain brewing areas. Ales are known for their bold, sweeter flavors and thanks to the variability of S cerevisiae’s characteristics, were made in many strengths and varieties to fit the needs of a populous that came to consume beer as their sole method of hydration.

Lagering caves cut into the Pennsylvania mountainside at the Yuengling brewery.

Central and Northern European brewing cultures had their own methods, but as with everyone in a pre-refrigeration world, they were concerned with preservation. Really, as a brewer, that is one of your few very small jobs in making beer. Beer is made by giving yeast a good home and preventing spoilage. In the case of these Europeans, they found that beer lasted longer when kept at consistent cooler temperatures in caves found throughout the area.  Here is where things start to get really interesting. Depending on your source, sometime during the 1400s or 1500s, brewers began to notice a change in the characteristics of their beers. The fermentation was taking significantly longer but the resulting beer was less sweet, crisp on the palate and much more clear. Beers fermented this way did not have the same top-fermenting characteristics and the fermentation stayed active with the yeast on the bottom. Something was definitely up and folks really liked it. Barring some weird wheat beer monopoly in Germany, beers fermented in this new style became the rage throughout Europe. Many of the German lager styles that we know today were invented during this time. The next 300 years were filled with this mystery beer.

It was not until the 1850s that we began to get an idea of what we were dealing with. Louis Pasteur’s discovery of yeast shed a ray of light on the glories of our favorite microorganism. Brewers were enlightened and a whole new world of scientific experimentation began. In 1883, Emil Christian Hansen, working at Carlsberg in Denmark, isolated a pure lager yeast strain and promptly named it Saccharomyces carlsbergensis, because they were paying the bills, I guess. It has since been more commonly named Saccharomyces pastorianus.

We also know now that this yeast species, while working best at cooler temperatures than S cerevisiae, also has the ability to further break down a certain trisaccharide called raffinose. Raffinose is a sugar molecule that is made up of fructose, glucose and galactose. S cerevisiae can crack off and use the fructose but leaves the disaccharide of galactose and glucose (called melibiose) behind. We detect this as part of the heavier sweetness attributed to ales. In the case of lagers, S pastorianus chops up melibiose as well, leaving a more dry beer behind with less residual sweetness.

Here we see raffinose at #1. Ale yeast and lager yeast both use the enzyme invertase to trim off fructose.(#3) S pastorianus has the capacity to crack the bond holding glucose and galactose together in the form of melibiose(#2) leaving a dryer finished beer.

What this discussion of these two species of yeast leaves us with, really, is that it should go without saying that ales and lagers are distinct and fully unique types of beers due to the wonderful organisms that are used in their production. Styles vary within the two categories, sharing ingredients and profiles, but the yeast and fermentation characteristics act as a very heavy dividing line. Tell your friends! Make sure they get it!

I know that this is getting long-winded, but there is something that we need to discuss. I said that lagers really came into their own in the 1500s. There is quite possibly a reason for this that we are just now discovering. S cerevisiae is critically important to me not only for producing booze but for being the first eukaryote to have its genome sequenced. We are pretty familiar with it as it is used in molecular biology – A LOT. Anyway, the genome of S pastorianus is huge in comparison to that of S cerevisiae and it has always been assumed to be a hybrid of S cerevisiae and another yeast, S bayanus. (Don’t forget that yeast can reproduce sexually, mixing genetic material.) S bayanus has similar characteristics as a bottom fermenting yeast that is commonly used in wine and cider production.

Gross but this is where S eubayanus comes from.

This was the prevailing theory until last year. In 2011, Saccharomyces eubayanus, a Patagonian yeast (yep, Argentina, in fucking South America) isolated from tree galls in cold beech forests, was discovered to contain 99.5% of the genetics in S pastorianus that does not belong to S cerevisiae! The new theory is that as trade ramped up with the New World, S eubayanus was brought over to Europe and began to infect brewing operations. When this new yeast made its way to the cold storage caves of Germany, it found a hell of a great place to live with consistent cool temperatures like the forests in Patagonia and sugar for free that it did not have to extract from a gnarly tree. There are some intricacies with this theory that are being hammered out but genetically, it looks like S eubayanus and S cerevisiae got down with a little sexy time and produced the lager that we know today.

So the next time you come across someone who doesn’t know the difference you can say that lager is the product of ale yeast getting down an exotic South American.

About Chris Washenberger


What is my favorite drink? Huh... That is a tough one. What do you have? That is probably it.

  • Smit 1855

    So why does the lager yeast release sulfer compounds?

    • Erik

      If I’m not mistaken the sulfur comes from organic sulfur-containing compounds, like some vitamins and amino acids, as well as also being formed from inorganic compounds in the wort like dimethyl sulfide, thiols and hydrogen sulfide. The sulfur coumponds are then reabsorbed by the yeast during lagering.