flat or pointy?
Just a wonderin' about the differences between flat bottom open fermenters and closed cylindriconical uni-tanks. I have the option to use either in my brewery (well, I only have one f.b.o.f., but it works). I've heard the flat bottom open tanks produce a more "pronounced" wheat beer, or German Alt. I'm sure surface area has something to do with this, but there has to be much more to it. So, who can explain the science behind this. If flat bottom open fermenters change the profile so much, what are the reasons? I'm SURE this will generate many responses, with all sorts of different theories, but I'm interested in what most of you have to say.
Flat or Pointy?
I can understand why a flat bottomed fermenter would give wheat beer a more pronounced characteristic...most wheat beers are unfiltered and most of the characteristics come from the yeast that resides in the fermenter...The cylindriconical tanks are excellent for dumping yeast. Most ales are gelatined and/or filtered, in which case you need to try to dump as much yeast out of the tank as possible, resulting in a cleaner more crisp ale. This is just my experience with the two styles of fermenters in my short career as a professional brewer. I also noticed that CIP cleaning a flat bottomed fermenter is a pain in the ass due to the draining issue. Those flat bottoms don't seem to want to drain and no one wants residual chemical in their tanks...
Ballast Point Brewing Co
San Diego, CA
You'll get slower fermentation in a flat bottomed fermenter and therefore more ester development as a general rule of thumb.
You may also get healthier yeast out of a flat bottomed horizontal fermenter.
Reasons? You get an awesome, turbulent fermentation with a cylindroconical. It has to do with additional head pressure in the cone and the tendency for yeast to drift to the bottom center of that cone. You get more fermentation down there in the center and the bubbles that nucleate down low in the cone get much larger as they travel to the top. This results in currents forming in the tank, with the beer and yeast in the center being carried upward and the beer on the sides being displaced and travelling downward.
All this keeps the yeast in suspension and fermenting quickly.
In contrast a flat bottom horizontal does not have yeast in the center and just sort of has a slower less dynamic fermentation. This would explain why you have more esters, including nasty hangover esters like ethyl acetate in beers fermented in horizontals. For this reason AB is crazy about horizontals and beechwood aging: it gives better ester development.
Horizontals have better yeast health because of less head pressure weighing down on the yeast. Anyone who has SCUBA dived can tell you that 30 feet of water pressure has a strage affect on the human body and it is the same case with yeast.
There is a little more to it, but that is the main performance difference. Cleaning as already mentioned is pretty different for these 2 types of tanks as well.