Brewing Beer: Yeast

Well, it's time for another technical talk at our homebrew club, but I won't be able to attend because of work schedules. So, here are some notes anyway.

Yeast turns the weak sugary water from the mash---that was boiled with the hops---into beer. The yeastie beasties eat the sugar and we drink their, ahem, p**s. It's a good deal for all concerned.

Yeast does come in a dry form, but most interesting yeasts only come in liquid form. There are two outfits that we locally use for liquid yeast: White Labs and Wyeast Labs. Besides their normal lineup, both these outfits will grow up most library yeasts for you or keep your own private yeast line for you.

Yeast is very important for the taste of beer. We as a club conduct experiments every time we have a megabrew and pitch different yeasts in carboys that ferment side by side, starting from the same wort. Sometimes the difference is astounding and unbelievable, except it just happens.

There are two general types of brewers yeast: top fermenting and bottom fermenting. The top variety is traditionally associated with ales and the bottom with lagers. Top yeast is so-called because they tend to grab gas bubbles and rise to the surface just after their most-active phase. Bottom yeast tended to sink and stay cleaner in old-fashioned open-top fermenters.

Modern day enclosed fermenters have blurred the effects and behavior of traditional yeasts, but the taste differences are still there. Ale yeasts are harvested out of the bottoms of conical fermenters these days.

You can delve into yeast ranching yourself, but most of us tend to stick with the commercial libraries. However, you can repitch lager yeasts about 5 times without restarting them and ale yeasts about 9 times. If you fish top yeast off the top of an open fermenter with a net, you can repitch practically forever---with the occasional acid wash---or homebrew wash.

Here's my advice: pick a beer style that is new to you, get its most characteristic yeast, and take a shot at it. Repitch the yeast a couple of times with the same recipe. Taste them and marvel at the complexity that is yeast.