View Full Version : Classic Stupid Stuff Question - Fermenters and Pressure

06-15-2014, 06:58 PM
I see lots of (most) breweries using fermenters that are rated for 14.7 PSI even though they never actually use them to hold any pressure. This is because they are fully vented while fermenting and then pumped to a brite tank to be force carbonated. These breweries range from the smallest new guys on the block to big regional guys that have a clear cut process and planned everything down to the smallest detail.

So why bother with over engineered tanks that can hold pressure when it is never actually used that way? Seems like there is significant money to be saved with a cheaper tank that is not pressure rated. What am I missing?

06-15-2014, 07:14 PM
Those fermenters that are pressure-rated certainly ARE used to hold pressure. Normally, a brewer would "spund" the tank with about 1P of fermentables before FG. This is really nothing more than using a relieving valve on the CIP arm to regulate the pressure to just under 1 bar as the beer finishes fermentation. This way you can naturally carbonate your beer to a higher degree than would be possible in an open (non-pressurized) fermenter. You still have to bump up the carbonation level after you have the beer cold in a BBT, but much less so. The resulting carbonation from a naturally carbonated beer is arguably finer than a beer that is fully forced-carbonated. That's why we spend the money on a pressure tank.

06-15-2014, 07:33 PM
You have to put co2 pressure on a sealed FV to cold crash it...unless you want to pull a vacuum or suck in a bunch of air.

06-15-2014, 10:28 PM
I have used spundigs in the past, plus all of my fermenters are rigged up as "unitanks" and I carbonate and usually package straight from the FV… plus, as noted you need to have pressure when crashing, and also when packaging out or transferring to another vessel

06-16-2014, 06:47 AM
The largest and most far reaching mistakes being made seem to be coming from " assumptions " being made without having had hands on or been in an environment where the Pros are running daily operations with time tested and well honed methods. This is especially noted in various attempts at cut corner engineering. Some of whats being proposed is truly unreal. Engineering is as it is for a reason.
Better stated: " Putting the cart before the horse " and " Attempting to reinvent the wheel."
This is all rising out of reading and imagining rather than careful study and hands on.
It will be found that the absolute best running plants are led by persons who understand the mechanical side of things fully.The best possible way to grasp the reality including the pitfalls is to tour working plants and get one's mind around what is happening without moving too fast. Very careful and methodical planning and study are advised.
The single best way to improve " on paper " engineering is with someone who knows how to handle engineered systems at an industrial facilities level.

06-16-2014, 08:00 AM
TonyT, you will have an abundance of CO2 pressure if you spund your tank correctly. The only way to suck a vacuum is to miss the 1 degree plato target to spund your fermenter to naturally carbonate. If you wait until FG to spund, then yes you could possibly pull a vacuum. So don't do that. Spund with 1 (or so--YRMV) degree Plato before you hit FG and then after you have built up a pressure to about 1 bar and you have hit FG, you will crash. Not before. Right? This is how it works: You spund and build this pressure in your pressure rated fermenter and carbonate your beer "naturally" (at least partially). Now if your fermentation temperature is 70F and you have 13 psi on your beer, you will have approximately 1.54 volumes of carbonation at FG. Please refer to carbonation charts online. Now you crash. Or wait for VDK rest or whatever. Point being is that you have as much pressure as your equipment can handle. 14.7 psi=1 atmosphere=1 bar. You should not get closer than about 90% to the setpoint on your Safety Relief Valve (SRV). They don't relieve at exactly 14.70000psi. Don't challenge them. Keep it around 13-14psi for a tiny bit of margin. Then when you crash, you would expect what? You will see the pressure slowly drop over many days as the beer at a colder temperature is able to hold more CO2 at that temperature. The beer will take this excess pressure and invite it inside the solution. Not likely in larger breweries with less surface to volume ratios. Now you gently transfer to BBT under AT LEAST THE SAME PRESSURE with a balance line (or umbilical line, or whatever they're calling them now). Then since the beer has been reduced to below it's saturation temperature, you may add more CO2 without seeing an increase in pressure. The beer at that point IS NOT SATURATED with CO2. So slowly add CO2 gently through a stone and watch THE FLOW RATE to keep the beer from foaming. And for God's sake, DO NOT VENT! When the pressure starts to climb in your BBT gauge, then you know that you have saturated the beer with CO2 at that temperature. Say you have a BBT at 13 psi and 38F. You are done and your beer is carbonated to 2.66 volumes. Perfectly acceptable for many beers. It does take a bit of thought to understand that cold beer holds more CO2 than warm beer and that changing your parameters changes the solubility of CO2 and the gas dynamics of your beer. But with a bit of practice, you can be carbonating perfectly with no waste of CO2, time, hair, or foam creation. Hope this helps, seems that carbonation is the bane of many newer breweries.

06-16-2014, 11:06 AM
Phillip, indeed. Just trying to cover all the factors at play...I don't think it's too far out there to assume that someone who doesn't understand why you need a pressure rated FV might also not be aware of the effects of temperature changes on an FV and how that relates to pressure, or be ready to purchase and implement proper spunding devices.