The life cycle of ale yeast is an extremely fascinating thing to see in action, that is, if you have the benefit of brewing beer in a glass carboy. First, during the initial "lag time," the yeast tends to collect near the bottom of the fermentation vessel, slowly moving and undulating into mushroom-like little clouds, collecting nutrients and oxygen. It looks like it is planning or scheming in some strange way. Then the next 3-5 days of intense growth and activity become infinitely more visually impressive. Suddenly, the yeast explodes with energy, releasing billions of microscopic carbon dioxide bubbles. The CO2 rises and carries the yeast molecules up with it to the top of the fermenting beer, where the gas escapes into a great foamy mass. The yeast continues to react fervently until it slows and clumps together (flocculates) with other yeast around it. These tiny globs fall back to the bottom, creating a sort of "circulating" effect. It is because of this heavy amount of action at the surface of the beer that ale yeast is known as "top-fermenting" yeast.
During the peak of activity, a fermenting ale looks like someone is swishing it around with some kind of huge invisible spoon! Yeast clumps are rising and falling with incredible intensity, foam is billowing from its surface - it really is quite amazing. Homebrewers may not like to admit it, but many of us, including myself, are "carboy watchers." Seriously, there really is nothing like staring into your carboy, observing the crazy party going on in there.
And you can't help but think to yourself - hey, my yeast are having a damn good time, right? I mean, they could be stuck fermenting some boring pile of bread dough, all sweaty and hot in the back of a pizza joint, but no, they somehow made their way into a sweet batch of homebrew - and they are rocking out! Think about it - the yeast organism does not have a huge amount of functions. Whenever someone asks me about yeast, I like to sum up their entire life with this analogy: yeast basically live to eat and reproduce, and then they "fart" pure carbon dioxide, and "pee" pure alcohol. Tell that story at a party and no one will ever forget how yeast works!
But seriously, to sit for just a moment and observe these tiny little creatures and their endless parade of insanity is actually quite calming. It really is nice to contemplate an organism with such a simple existence, doing it's simple task, creating this amazing beverage we call beer. And to think, for thousands of years people never even knew they existed!
Aaaah, carboy watching - call me crazy, but it's just another thing that I love about homebrewing.