Without naming any names, this man I know who brews his own beer would like to see a blog post about what the deal is with yeast.

Here are the basics:
Yeasts are a type of fungus.  Most fungi are multicellular, like mushrooms, but yeasts are unicellular (or single-celled, whichever you want to say is fine).

Don’t confuse yeasts with bacteria.  I know they both are single-celled, but that’s pretty much all they have in common.  Yeasts have a nucleus and organelles, and bacteria don’t. Also, yeasts are around 50 times bigger than bacteria.

Yeasts are known for a few things, but I’m going to focus on one in particular: their role in producing alcoholic beverages.

When yeasts have oxygen around, they behave much the way that our cells do.  They bring in sugar and break it down to get energy and release CO2.  For reasons I won’t get into, this process is most efficient when oxygen is around (it has to do with oxygen accepting electrons–see? Did you really want to know that?)

BUT, when there isn’t any oxygen around, the system makes a switch and the process creates ethanol (a type of alcohol) as a side product.

Here is the human equivalent:  When your muscle cells have a good supply of oxygen from your blood, they can get a lot of energy, and in turn, do great things for you when you are exercising.  But if these cells don’t get enough oxygen (because you’re out of shape and your lungs and heart aren’t up to the task), they’ll still do what they have to do, but they will switch gears and work without oxygen.  This will produce lactic acid (instead of alcohol because, well, we’re not yeast) as a waste product, which is what causes muscle cramps.  

So the process of creating beer or wine (or whatever other alcoholic concoction you want) takes advantage of yeasts’ abilities.  Beer brewers mix a variety of grains and spices and add a certain variety of yeast (there are hundreds), and the yeast eats all the lovely sugars in the mix and release CO2 (carbonation) and ethanol (alcohol).  This whole process is called fermentation, and beer brewers get all starry-eyed when you mention it.  They may also drool.

A big part of beer brewing involves keeping the yeast happy.  You want them to ferment at the right temperature, with the right amount of sugar, and without any unwanted guests.  It’s important that the beer mixture not be infiltrated by unwanted bacteria, which can ruin the taste of the beer, and generally annoy the yeast that has a job to do.

Beer brewers go to great lengths to keep yeast happy because they so appreciate what yeast do, but sometimes I really feel like the yeast are taking advantage.  Just a feeling.