Bare-Bones Basics #5: Yeast

Yeast Cells Under a Microscope

Yeast Cells Under a Microscope

The thing that makes brewing beer work, or, more generally, the thing that makes ethanol in general, is yeast. (Now, you can synthesize ethanol, industrially, through the hydration of ethylene, but this involves using some nasty chemicals that don’t belong in something you plan on drinking.) Yeast, as you probably know, eats sugars in your beer and (as Tim likes to put it) poop out alcohol.

Yeast is a single-cell fungus, which is found just about everywhere. All types of yeast reproduce asexually, though there is a process of genetic material exchange between cells. The yeast species you are probably most familier with is saccharomyces cerevisiae, ale yeast. This is actually the same specie as baking yeast, but in general, brewers use a less aggressive yeast strain that produces fewer unwanted chemicals that would give the beer an undesireable taste. Saccharomyces carlsbergenis, called so because it was first isolated by Carlsberg, also known as saccharomyces pastorianus or lager yeast, is, unshockingly, used in lagers. Saccharomyces carlsbergenis is a combination of saccharomyces cerevisiae and a third type of yeast, used mostly in wine and ciders, saccharomyces bayanus.

The thing most important for your beer that you need to know about the differences in these yeasts is that lager yeast generally has higher attenuation, meaning it can eat more sugars, leaving your beer more dry (though the variation in strains of each lager and ale yeast provides a large overlap), and that it works at a colder temperature (about 10-15 F colder) than ale yeast.

All alcohol-producing yeast can work in two different ways, based on if there is oxygen around or not. When yeast eats sugars without oxygen, the yeast gives off the waste of ethanol, and carbon dioxide, along with some energy. This energy does two things, it powers the yeast cell, so it can grow, and warms the liquid it is in. When there is oxygen present, the yeast cell can completely break down the sugar into water and carbon dioxide. This produces significanly more energy for the yeast cell, which lets it grow much faster.

When you add your yeast to your wort, you want some oxygen to rapidly grow your yeast so fermentation doesn’t take a long time. Once the yeast has consumed all the oxygen in the wort, it then switches to anarobic fermentation (without oxygen) and makes ethanol. If you have a large quantity of yeast cells to start with, you don’t have to oxygenate your wort as much, and you’ll get higher alcohol concentrations (and less water) in your beer.

Another stat you may see on the side of your yeast pack is ‘flocculation’. Flocculation means the ‘clumping’ of yeast cells in your beer. This sounds like it might be a bad thing, but actually it’s good. When your yeast cells are done eating sugars, they can do one of two things: with yeast that has a low flocculation, it will just sit suspended in the beer. High flocculation means the cells will clump together and float to the top, in the case of ale yeast, or sink to the bottom, in the case of lager yeast. This will make your beer clearer. Some beer styles are traditionally cloudy with yeast, and has a slightly different taste because of it.

Some of you may notice I didn’t mention brettanomyces, a genus of yeast used in making lambics. This yeast is naturally found in the air in the southwest of Belgium. Lambics are made, not by adding yeast directly to the wort, but by allowing them open access to the air. The yeast particles in the air fall into the beer, instead of physically putting a yeast solution into the beer. This yeast gives lambics a distinctive sour taste. This open fermentation, you might think, wouldn’t work, because it isn’t separated from the air. If the wort is exposed to the air, it will have access to oxygen, and the yeast would never anaerobicly ferment the sugars into ethanol. However, if you remember part of what is released is carbon dioxide. CO2 is heavier than air and sits on top of the wort, creating a barrier between the oxygen in the air and the wort, allowing fermentation.

White Lab Varieties

White Lab Varieties

There are many different strains of each of these species of yeast. Each have slightly different characteristics that will produce slightly different results. More or less flocculation, more or less attenuation, higher or lower prefered fermentation temperatures, etc. These allow you to fine tune your beer, in a general sense, the important distinguishing factor is ale yeast, lager yeast, or lambic yeast. This hopefully helps you understand how yeast works, and gives you a better idea as to what is happening inside your carboy.

Tasting Notes – One Wort Twenty Yeasts

Waaaay back in early June, Original Gravity Brewing in Milan hosted the Ann Arbor Brewer’s Guild for the One wort 20 yeasts experiment. The concept is… exactly as it sounds. The same wort was fermented with twenty different White Labs yeasts, in order to examine the effect that yeast strain had on the final taste of the beer.

The official AABG tasting notes can be found on their website, and our notes are listed after the yeast strain for each of the different beers that we tried. I’ll go out on a limb and say their notes are much more detailed than ours (but then, most of them have been brewing and drinking a lot longer than we have):

  1. WLP001 California Ale Yeast
  2. WLP002 English Ale Yeast
  3. WLP004 Irish Ale Yeast
  4. WLP005 British Ale Yeast
  5. WLP007 Dry English Ale Yeast – Less hoppy than 9.
  6. WLP008 East Coast Ale Yeast
  7. WLP009 Australian Ale Yeast
  8. WLP011 European Ale Yeast – Slightly dry, earthy, not as hoppy.
  9. WLP028 Edinburgh Scottish Ale Yeast More full than 5.
  10. WLP029 German Ale/Kolsch Yeast
  11. WLP036 Dusseldorf Alt Yeast – Citrus. Slight more malty than 8. We may have switched cups here, because this one tasted more like a trappist.
  12. WLP041 Pacific Ale Yeast
  13. WLP051 California Ale Yeast – More citrus than 1. Ester flavors.
  14. WLP060 American Ale Yeast Blend
  15. WLP080 Cream Ale Yeast Blend – Texture thicker than #4, but more dry.
  16. WLP500 Trappist Ale Yeast
  17. WLP550 Belgian Ale Yeast
  18. WLP566 Belgian Saison II Yeast
  19. WLP810 San Francisco Lager Yeast
  20. WLP862 Cry Havoc – Black pepper flavor.

Note that most of our notes are simply comparisons to another of the yeasts – because we tried them in batches of three or four. Some of them may have gotten… confused. More in-depth notes may or may not be posted at a later date.