I thought it would be good to talk about yeast: the magic little organism that turns sugars into alcohol through the process of fermentation.
I won’t go into the fermentation process, but if you’re curious, the Wikipedia articles are quite easy to follow. Fermentation in general can be found here – this article is not specifically about alcohol fermentation, but explains the process in general. Alcoholic fermentation information can be found here for further reading.
Yeast in general:
Really, you can use any kind of yeast for fermentation, even regular baker’s yeast bought at the super market, but the various brewing yeasts are specifically designed for taste and alcohol tolerance.
On that note, it is possible to kill your yeast if the alcohol content of your brew gets to high. At this point, you can’t really get anymore fermentation going because even if you add more yeast, that will probably die too! Then you’re left with a half fermented beer that still has lots of sugars in it, which would probably taste quite interesting, but not in a good way. Don’t worry too much though, it’s easy to track down yeasts that will be good well into the high teens/twenties on alcohol percentages; these are generally wine making yeasts.
If you’re making a cider or anything with fruit, it’s also possible to use the wild yeast that naturally grows on fruit peels. In fact, my mother uses this to make home made vinegar: her most interesting concoction was a banana vinegar! The problem with using wild yeast is ensuring that it’s only the wild yeast that goes into your wort (or juice if doing cider) and not other bugs that will mess up your brew. I have yet to attempt this, but it may be fun!
Yeast and temperature:
Yeast is pretty resilient, so if it gets too cold, you won’t kill it. It just gets a bit sleepy and slows down a bit. You can even freeze yeast if you want to preserve it. This means that even if your wort gets a bit cold, things will keep working, just more slowly. Although this isn’t too bad, be aware that if your wort is in the fermenting tub for too long, sediments may begin to taint the taste of your beer.
On the other side though, if your yeast gets too hot, it will probably die, just like anything else. So although heat will help speed up the fermentation process, there is a point where you won’t get anymore benefit and the heat will actually be detrimental. Make sure your wort is at specified temperatures before pitching your yeast.
Experimenting with yeast:
Of course it’s easiest to simply buy yeast from your local home brew supply store, but experimenting with different kinds of yeast can be a bit of fun. The different strains that you can buy at a good home brew supply store have different characteristics for taste, optimal temperature, and alcohol tolerance. This means that you’ll use a different yeast for different kinds of beers.
For example, there are specific kinds of yeast for ales, lagers, and wines. With the few cider experiments I’ve done, I’ve always used an SN9 wine yeast and been happy with the results. As it’s not desirable in a cider/wine, this type of yeast doesn’t leave any taste behind. Sometimes you want some of that taste in your brew, and you can generally find a yeast that will do that for you.
That’s it on yeast for now!