Let’s face it, the yeast is doing all the heavy lifting. Yeast is what makes beer BEER, and not just hoppy sugar-water that’s cloyingly too sweet to drink. But the yeast is doing a lot more than just creating alcohol content. Two beers with identical grain bills and hop schedules can taste radically different if fermented with different yeasts. Unfortunately, with a lot of cheap extract kits, there’s usually some sort of anonymous “ale yeast” taped to the lid of the can. With this sort of example, it’s easy for newcomers to misunderstand just how important yeast is to beer.
There are two major types of brewers yeast; ale yeasts and lager yeast. Ale yeast is a top fermenting yeast that works best in warmer temperatures (~60 – 75 dF), and produces more fruity esters. Lager yeasts are bottom fermenters, enjoy cooler temperatures and produce very clean fermentation characteristics. Due to the cooler temperatures, lager yeasts require more time to reach full attenuation. It’s not uncommon for homebrewers to allow their lagers to condition at low temperatures for two or three months . . . or more.
Homebrewers have access to yeast in both liquid and dry forms. However, I enjoy the simplicity of dry yeasts. If I need a neutral, unobtrusive yeast for an American APA, I like Safale US-05. However, if I want a yeast with more fruity, and estery characteristics for a British Ale, I’ll go with Danstar Nottingham. If I’m brewing a particularly eccentric beer, I might pick a yeast that is specifically designed to suit the brew. But overall, “Notty” and US-05 are my workhorse yeasts.
For some excellent information about all things yeast (as it applies to beer brewing), get your hands on a copy of “Yeast: The Practical Guide to Beer Fermentation”.