Thinking about Sam's having mentioned the "starter" method of dealing with liquid yeast, I guess I should address it a bit to explain what it is all about and the easiest way to do it. This is most applicable to people using liquid yeast rather than dry yeast. (Both of the above preparations are "live", just because it is dry doesn't mean it's dead.)
Yeast multiply by budding. That means that their growth is not arithmetic, but rather geometric. Every reproduction cycle doubles your yeast population. (1,2,4,8,16,32,64,128,256,... but starting with upwards of 100 billion cells and ramping up from there.) The more yeast you've got, the quicker they can eat all the sugar in your wort, and the less chance anything else has to get established in there. To really give your yeast a kick-start, which is the idea behind the starter technique, you let them warm up a little and multiply a few times before they actually get pitched into your wort. ("Pitch" is brewer speak for tossing yeast into wort.) That way, there are more of them, they do their work quicker, and your beer benefits. This is not, however, to say that more yeast is always better. If you end up with too many yeast going at it all at once, you risk overproduction of the yeast's flavorful esters and phenolic compounds, and some yeasts produce their characteristic flavors more effectively when stressed, rather than when pampered. But it is easier to underpitch than to overpitch yeast.
Now the question becomes where and how to let the yeast warm up and reproduce a couple of times. Sam's method, below, does work fine... but there is a simple shortcut that can make it even easier. Instead of worrying about mixing up some dry malt and water and hops, you can (in most parts of the US at least) purchase unfermented bottled malt beverages. The brand I know is Malta Goya, but there are others out there too. You'll find them in hispanic markets, and often in the "ethnic" aisle of your supermarket. They're priced like soda, or cheaper, and are of the right sugar concentration for yeast to comfortably get warmed up for beer fermenting.
A bottle of malta emptied into a sanitized glass container is a fine training ground for your yeast. So, follow the instructions on your yeast package with regard to activating any internal nutrients that might be in there (Wyeast does this, others do not), and then add the yeast to the malta and cover up the vessel to keep airborne stuff out of it. In a day or two you'll see a sediment building up on the bottom of the vessel. That sediment is yeast cells that you can use to ferment your beer. Refrigerating the starter will encourage more of the yeast cells in there to fall out of suspension and join the cake on the bottom. That way you can decant most of the liquid (and the maltas are dark and might darken your beer if added) and just add the slurry of yeast cells that built up.
For beginners using fresh modern dry yeast in a two gallon batch, you really don't have to worry about this step. Once you graduate to five gallon batches and start exploring the varieties of yeast that are available in liquid but not in dry form, then this step will aid you in maximizing the deliciousness of your beer.
In re to using live cultures of liquid yeast, one way to really kick off the fermentation is to brew a small "pitching batch" a few days before so you can grow up some extra yeast (Chris may be planning on explaining this later). This is easy to do, since you don't really care about the taste: smack the pack & when it is inflated, boil some malt powder (maybe with a few pellets of hops) with maybe a quart of water, decant it into a sanitized glass bottle and chill, pitch the yeast and put on an airlock. In a day or two, the yeast will have fermented the liquid into "beer." What's more important is that the population of yeast cells you have on hand will have radically increased. While you're boiling your wort, etc. just put the bottle in the refrigerator so most of the yeast goes temporarily dormant and sinks to the bottom of the bottle. Decant off most of the liquid, and when it is time to pitch the yeast for your actual batch of beer just swirl the bottle to stir up the yeast and pour it into your fermenter.
Edited by cdh, 10 April 2006 - 07:41 AM.