"So, what happens in all these tanks?"

That was the question that we heard at the last beer dinner.  It took us aback.  When you're so familiar with the tools of your trade you tend to forget that to some people brewing is still such a mystery; some bit of alchemy left over from the middle ages, or so technologically complicated that it would be useless to explain.  It's neither of those things, actually. 

Let's start with those tanks.  You know the ones, looming behind the bar like so many stainless sentinels.  Every brewery has them, but really, what the f**k do they do?

They're fermenters, is the short answer.  Which is always met with a nod and then, "So they ferment the beer"?

Well, no, the yeast ferments the "wort"  inside the fermenters which will eventually become beer...

"Uh-huh".

OK, listen closely and stay with us.  Brewers make wort from malted barley, hops and water; yeast metabolizes the sugars in wort to make beer but that can't happen just anywhere, so, we use fermenters. Fermenters are large, stainless steel, temperature controlled, self-contained little universes for yeast to do their thing.  They're stainless because it is an inert metal that is easily cleaned with strong chemicals and easily sanitized with even stronger sanitizers.  They are temperature controlled because fermentation is exothermic (it puts off energy as heat).  But if there is too much heat then fermentation speeds up.  Fast fermentations produce off flavors and aromas that can be, well, nasty, so we control the speed by controlling the environment; that is, we keep it cool inside the fermenter.  Each fermenter has a series of double-walls on the outside called "jackets".  Through these jackets we are able to run glycol; a food grade antifreeze, really, but for our purposes it acts as a heat transfer solution.  As it passes through the jackets it picks up heat from the fermentation and carries it back to a central reservoir where it is chilled down again to 25˚F and then it continues its journey back to the fermenters.  Each fermenter has its own thermostat that regulates the flow of glycol through a solenoid valve based on temperature; too cool then it closes the solenoid and no glycol, too warm, and then it opens the solenoid and here comes the glycol until the wort hits its pre-set temperature.

Fermenters have a specific shape (cylindro-conical) as well.  When fermentation is complete yeast cells tend to clump together, or flocculate; when this happens the larger groups of cells sink to the bottom of the fermenter.  Now, these cells are perfectly good cells and it's our intention to use them again, or re-pitch them, in another beer in another fermenter.  But if the fermenter is flat on the bottom then it is very difficult to get to the good, healthy yeast.  That's where the cone comes in; dead cells tend to drop out first and fill the first 12 inches of the cone.  On top of that rests the very healthy cells that we need to re-pitch.  On top of that are the cells that are alive but don't want to cooperate and flocculate very slowly (in fact, if these cells are selected to re-pitch then that entire fermenter will have these unwanted characteristics; a bit of natural selection, if you will).  So, we open the fermenter and dump the dead cells.  We then take a sample of the middle level of cells and determine how viable they are in the lab and then re-pitch them according to that viability equation, leaving the uncooperative little bastards behind.

Did you get all that?  Good, so, now when you are with someone in the back bar and they ask, "What happens in all these tanks?" you don't have to squint and say, "Uh... magic?"