Barley Mowat 

20 Facts You Very Likely Already Knew About Yeast

with 9 comments

While doing some research for another article… No? You don’t buy me doing research? Okay, fine, I was drunk and bored then. Yeah, I thought you’d buy that one. So, while I was drunk, bored and done with the porn, I surfed randomly and stumbled across a few interesting facts about yeast. Most likely you already know most of these, but if I’m lucky there’s a few newbies. I’d also be surprised if anyone didn’t know the first batch, but I’ll keep them in for completeness.

The raw basics (Skip if you have a beard)

  1. Yeast is a single-celled, asexually reproducing fungus. Hey, I said we’re starting basic, didn’t I?
  2. “Lager yeasts” are bottom-fermenting, meaning they fall to the bottom of the beer during fermentation. “Ale yeasts” do the opposite.
  3. Lager yeasts ferment beer at a much cooler temperature than ale, and at a slower rate. In fact, lager yeasts were first discovered in the early 1400s because beers fermented during winter had a lighter, crisper taste than those fermented in the summer.
  4. While Saccharomyces cerevisiae (ale) and Saccharomyces pastorianus (Lager) are the most famous examples of each, there are dozens of closely related species that can be used in brewing beer. Most commercially purchased strains, though, are variants of those two.
  5. Yeast metabolizes sugar into carbon dioxide and alcohol; this gives beer it’s two distinct properties of carbonation and awesomeness.
  6. It’s common to refer to the carbonation produced by yeast as “yeast farts” since it’s a gaseous product of cellular respiration. I guess that makes the liquid product (booze) “yeast piss.”


Yeast is also responsible for vague, blurry ads that somehow make me uncomfortable.

Slightly more interesting

  1. The Spanish “cerveza” is derived from the Latin “cerevisia”, which is the name of the top-fermenting ale yeast, so when you order that cold Central American Lager on a beach in Mexico, you’re really asking for an ale, and really, wouldn’t you prefer a beer with actual flavour?
  2. S. pastorianus used to be called S. carlsbergensis. It was identified in the late 19th century by, you guessed it, Carlsberg Brewery (or rather, their research arm. Yes, they have a research arm).
  3. S. cerevisiae is also used to make wine and bread. Wine was easier to do, though, because it grows naturally on the skin of grapes.
  4. Some yeasts outside of the Saccharomyces genus entirely are also commonly used in brewing beer, with Brettanomyces bruxellensis being a notable one (although almost always in conjunction with regular yeast). This is the “Brett” in Brett-conditioned beers. This yeast also occurs naturally on the skin of wine grapes.
  5. Despite the fact that yeast produces carbon dioxide, it isn’t enough to carbonate beer to the levels consumers expect. Thus, that beer in your hand has been artificially, or “force” carbonated. (See Dean from Lighthouse Brewing’s comment below for info on alternatives)
  6. The “sour” in sour beers is not yeast at all, but rather the bacteria Lactobacillus brevis and Pediococcus cerevisiae amongst others.
  7. It’s very hard to actually kill yeast. You can starve it, dry it out and even freeze it, but if you give it a little sugar and some water… bam! Booze!
  8. Yeast doesn’t just straight up convert sugar into liquor, it lazily slowly converts it to intermediary products first, and only goes back to finish the job once all the yummy sugar is gone. Incomplete fermentation can leave lots of these intermediaries lying around, causing off flavours in beer.
  9. Yeast is also finicky. It can just up and quit, saying “fuck this” while storming off the job. This is known as a stuck fermentation, and while you can sometimes get it going again by adding new yeast (scabs!), it’s not always possible.
  10. Breweries often maintain their own standing colonies of yeast, rather than buying new supplies at the start of each brew. Since yeast evolves very quickly, breweries often also breed them for specific flavours and characteristics, resulting in custom sub-species specific to each brewery.
  11. Yeast is everywhere: on your keyboard, in the air, in your hair and on your skin. Before modern times brewers wouldn’t add yeast to their wort–they’d just expose it to the air for a bit.

Very interesting

  1. Brettanomyces bruxellensis (see above) is actually a specifically cultured version of the wild yeast regional to lower Belgium. This is why traditional (wild fermented) Belgians from that area have Brett characteristics. We also have local species of wild yeasts in Vancouver, but no one brews with them (yet).
  2. It was recently determined that S. pastorianus is actually a hybrid of S. cerevisiae and S. eubayanus which is less than interesting until you realize that S. eubayanus is native to Patagonia and that S. pastorianus became common in European brewing in the early 1400s.
  3. All these yeasts produce liquor aerobically, or in the presence of oxygen. Many other yeasts will only do so anaerobically, like Kluyveromyces lactis. Add in oxygen, and they’ll completely convert your precious barley malt into CO2 and water, the greedy bastards. Deprive them of O2, though, and you have a new weird beer that geeks might buy!

And there ya have it. I’m no longer bored, or maybe I’m now too bored to continue blogging. I don’t know which. I think I’ll go have a beer.

Written by chuck

January 16th, 2013 at 8:01 pm

Posted in Beer and You

9 Responses to '20 Facts You Very Likely Already Knew About Yeast'

Subscribe to comments with RSS or TrackBack to '20 Facts You Very Likely Already Knew About Yeast'.

  1. Unlike nitrogen, carbon dioxide dissolves quite readily into aqueous solutions, and the resulting degree of ‘carbonation’ is a simple relationship between temperature of the liquid and the pressure of the gas. A fermenting beer produces many time more volumes of CO2 than would be required for adequate carbonation, and by carefully controlling the back-pressure of a fermenting beer as CO2 is liberated, you end up with a perfectly carbonated tank of beer. This method of ‘natural’ carbonation is quite common, especially in craft breweries. All Lighthouse beers are carbonated in this way.

    Dean

    17 Jan 13 at 07:04

  2. @Dean – Thanks for the clarification. I had previously assumed that Lighthouse was using back-pressure to only partially carbonate then topping up. It’s a good way to save money, for sure!

    chuck

    17 Jan 13 at 09:26

  3. @Dean – Learn something new every day – thanks! Is the practice relatively common in commercial breweries?

    @Chuck – If you want to read more about yeast, ‘Yeast: The Practical Guide” is a good read. http://www.amazon.com/Yeast-Practical-Fermentation-Brewing-Elements/dp/0937381969

    Jeff

    19 Jan 13 at 09:23

  4. Hey Jeff
    Not common in big breweries as it tends to play havoc with their flash pasteurisers. They will often recover CO2 from their ferments and re-use it to force carbonate once the beer has been filtered and processed.

    Dean

    20 Jan 13 at 10:35

  5. [...] lager”) vs Saccharomyces cerevisiae for ale (you can learn more about yeast on my own blog here). Feel like a geek yet? We’re just getting started! The term lager itself comes from the [...]

  6. Never thought of yeasts from different regions, especially Belgium! Loved the ‘The Spanish “cerveza” is derived from the Latin “cerevisia”’ Ale fact haha. Good read.

    HomeBeers.org

    11 Mar 13 at 09:39

  7. Never thought of yeasts from different regions, especially Belgium! Loved the ‘The Spanish “cerveza” is derived from the Latin “cerevisia”’ Ale fact haha. Good read.

  8. you suck men

    kitty

    16 Feb 14 at 16:28

  9. I think you guys need to get a life because I don’t think you have one. You just talk about crap all day long.!!!!!!

    carl

    4 Oct 14 at 06:07

Leave a Reply