When I pour the pints of flocculated yeast left in the bottom of my carboy down the sink, I feel a twinge of regret. As the scummy sludge burbles its way down the drain, I say a brief prayer, thanking the little guys for their work, hoping each bud survives its passage through the sewage system.

I am a home brewer, a yeast farmer. I have felt the cool release of carbon dioxide on my palm held above my airlock as it rhythmically clacks away, marking the work of millions upon millions of yeast, busy converting sunlight into alcohol.

I love the end result as much as anyone who breathes, but I cannot romanticize away the burden I put these critters through. So pour yourself an ale, let the foam caress your upper lip, and relax--it is time you know just how much that beer cost a fellow organism.

***

Yeast is a facultative anaerobe--that does not mean, however, that it does not appreciate a breath of oxygen now and then. As any decent home brewer will tell you (and I confess few of us rise to the category of "decent"), the wort (the lovely malt, hopped extract that feeds the yeast--fetal beer) should be aerated prior to pitching the yeast.

Despite the high falutin' language, "aerating" involves nothing more than sloshing the wort around, rolling the carboy on the kitchen floor for a few minutes. With good nutrients, and a dose of good air, the yeast go into an asexual frenzy, budding like there's no tomorrow, producing gazillions of fellow yeasts, so that soon each cc of wort contains 50 million yeasties.

But (and this is THE key point)--happy yeast with lots of nutrients and oxygen do not make ethanol. They (like you and me) breathe, respire, and convert carbohydrates into water and CO2. They screw like mad, play and live and (perhaps) whistle delightedly to themselves but (again I will repeat the take home message, as a teacher will), no ethanol. No hooch. No demon alcohol.

Making alcohol requires, ironically, stress. To make alcohol, the yeast must be put in an environment that has little oxygen.

So I torture them.

I put an airlock on my carboy, and the little critters consume the oxygen they have. In order to survive, they switch over to anaerobic metabolism--you and I, we'd take the easy way out and suffocate, but the yeasties are far more evolved than we are.

So they say:

"Ha, ha, ha, Mr. Doyle, despite your diabolical airlock, we can still screw with impunity in your carboy, happy, happy, happy critters we are, with our sophisticated facultative anaerobic metabolism, that will allow us to supercede humans when the atmosphere is nothing but charred CO2 and sulfur dust...."

This makes me sad. If I were power hungry, I suppose I might glean some glee from this, but I know this will end with me sharing bottles of ale with my obligatory aerobic friends. You see, as the yeasties play joyfully among themselves, they neglect a small problem. When they switch to anaerobic metabolism, they make alcohol.

And while the yeasties are more advanced than most humans, like most humans, they are susceptible to ethanol. Once the wort reaches a certain level of alcohol, the yeast pass out and sink to the bottom of the carboy, dazed but not quite dead.

And like the male of our species, a drunk yeastie can no more reproduce than a tonerless xerox machine.

So a toast to my finely evolved buddies, and an appreciation for the complex life cycles these little guys have gone through so that you may enjoy your ale.

I hope that an ale will never be just an ale to you, my friend, for knowing the struggle that went into that bottle can only make you more versed in the complexity and relatedness of this universe, too beautiful to comprehend.