Forgive me of any apparent stupidity, but how is a square of plexiglass or undrilled bucket lid an open system? No airlock or blowoff to allow CO2 to exit, unless the cover is removed from time to time or is slightly ajar? Just trying to visualize this, thanks for the help NQ3X. Ringwood is competing with Wyeast 1968 for the next series of brews.
No stupidity at all. The positive pressure of the emitted CO2 will allow it to escape the vessel; no need to leave anything ajar. CO2 will exit. When the beer stops rapidly devolving CO2, the lid just drops into place. Positive pressure keeps nasties out.
In
true open fermentation, the only thing protecting your beer is the krauesen. It requires a clean fermentation room and a lot of minute attention to pull that off, because once the krauesen settles, the risk of contamination increases exponentially. Commercial breweries can use true open fermenters - they've got someone watching the ferment all day, every day. As soon as the krauesen falls (or is skimmed), the green beer is racked. Homebrewers generally lack the luxury to watch the ferment that closely.
Putting a clean, sanitized sheet of clear Plexiglas over the mouth of your bucket not only keeps stuff from falling in, it allows you to visually inspect the ferment.
I suppose my use of fermenter geometry was really looking at the reducing space about the krausen line in a carboy, which would result in greater pressure on the yeast. Correct?
Not really - I think it has more to do with pressure in atmospheres. A closed system will not devolve CO2 as freely as open. I don't know the bio-science underlying the phenomenon, but I experienced a marked difference in Ringwood's performance between open fermenters and unitanks.
There was a beer we brewed in 10bbl batches, knocking out into the 12bbl open fermenters referenced above. After full attenuation was reached - usually about four days - the tanks were crashed from 72 to 35F over three days. Then the beer was racked to a 25bbl horizontal lagering tank, dry-hopped, and allowed to rest for another week before filtering and packaging.
We developed the recipe for a 15bbl batch, hoping to improve efficency and lower man-hours by casting into a unitank. Trouble was, Ringwood simply refused to properly attenuate in the unitank. It would petulantly refuse to drop that final 1-2P. The
real trouble was, because we weren't pasteurizing (and even 1-micron filtration doesn't result in sterile beer), the bottles were undergoing an uncontrolled secondary ferment and overcarbonating (sometimes even generating grenades).
It's weird. The only variable we couldn't control through technique was the liquid pressure and gas pressure in the headspace. Now, that gas pressure wasn't much - it's not as though we were spunding; we were essentially using a homebrew blowoff tube writ large - but the constricted blowoff of the conical ferment compared to the gentle devolution of gas in the open tank seemed the obvious culprit.
There. Now you know one of my dirty secrets: Pro brewer inadvertently makes bottle-bombs!
Bob
