I don't draw a vacuum in the tank as this would obviously cause uncontrollable foaming even if the tank were capable of withstanding it without damage. The vacuum is only drawn in the contraption after the hops have been loaded with the 3" valve firmly closed. Several evacuation/purge cycles are run, much like in a bottle filler, before the contraption is finally pressurized to a pressure equal to the tank's internal pressure after which the valve is fully opened to drop in the hops.
Cold crash Unitank
- Thread starter Tonypr24
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I didn't think you were drawing a vacuum on the full tank (but if someone were to do so, yes that's another hopefully obvious consideration). More that if you rig up an enclosed chamber atop the tank to be sure it can handle the pressure requirements, both positive and negative. I know some of your readily available vacuum pumps are designed for evacuating HVAC systems and can produce a good bit of negative pressure.
Obviously however you've got yours set up is working, so that's awesome.
This is actually relevant to the original topic as well, most fermenters should be able to handle the small negative pressure of crashing from fermentation temps to cold crash temps, but would immediately suck in as soon as the seal was broken.
However, if you took a much larger temp/pressure change, say from heat pasteurizing an empty fermenter, sealing hot at atmospheric pressure and the letting cool to room temp, that can generate enough negative pressure to fully collapse a fermenter.
However, if you took a much larger temp/pressure change, say from heat pasteurizing an empty fermenter, sealing hot at atmospheric pressure and the letting cool to room temp, that can generate enough negative pressure to fully collapse a fermenter.
(I don't know if the PRV that SSBT has is also antivac, the ones that I use are typically +15psi and -0.5psi)
From what I know the SSBT valve does not help with a vaccum. I was looking at brewershardwarw for theirs that's about 100 bucks. Either that or just risking my first unborn to a spunding valve. (Adding that just to stir the pot)
Yeah, antivac ones aren't cheap. Given that SSBTs PRVs are like $40 I'd be surprised if they were vacuum breakers too.
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And even then a vacuum breaker is a safety device as well- it'll let air in to break the vacuum. Not good for beer, but better than tank collapse.
The chamber is attached directly to the 3" butterfly valve so the vacuum is actually only acting on the valve mechanism. That valve is a massive chunk of metal. I believe it's rated to over 10 bar so the 0.8 bar increase in pressure differential due to the vacuum doesn't really affect it in any way.
Low oxygen brewing has a great article discussing the calculations and effectiveness of purging a volume of air (a keg in this case) of all oxygen. The theoretical amount of oxygen (measured in ppm) remaining in the dry hop spool should be the same figures that exist in the table of purge pressure vs purge cycles, if one where to not use a vacuum pump to evacuate the spool before each flush of CO2.
http://www.lowoxygenbrewing.com/bre...rging-transferring-stabilizing-finished-beer/
My calculations could be wrong here but assuming that vacuum is space devoid of all matter, and the level of vacuum obtained by the evacuation of the spool is at least 97% (medium vacuum, it could be more) each time. One could assume that the 21% or 210,000 ppm of oxygen that exists in the spool at the beginning should be reduced to 3% of this total, or 6300 ppm after the first evacuation. If the spool is now filled with CO2 to a pressure of 15 psig, then simply purged by dropping its pressure back to ambient atmosphere via venting. The O2 concentration should drop to:
O2 conc_new = O2 conc_old * Vac_pres_abs / (Purge_pres_abs)
or
(6300 ppm * 0.44 psia) / (14.7 + 15psig) = 93.3 ppm O2
From the chart this would be the equivalent of purging the spool 11 times at 15 psi. If we run the evacuate, purge, and vent process once more the concentration of O2 should drop too 0.041 ppm. Filling the spool one last time with CO2 to 15psig to equalize the head pressure with the spool before the hop drop should drop the O2 concentration of the spool to near zero ppm. This would be the equivalent of purging the spool 19 times at 20 psi. When the hops are dropped the concentration will reduce more as the small volume of gas in the spool mixes with the larger volume in the headspace.
Edit: corrected for not accounting for second evacuation cycle
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A pump capable of obtaining that level of vacuum has non-food grade oil in it and there's always the possibility of it migrating upstream. I really would not recommend taking the risk as the effects of ingesting oil are really unpleasant. A mechanical, oil-less pump can reach 0.8 bar vacuum requiring just a few more cycles thus using up a bit more CO2 but since the volume is relatively small the CO2 consumption is still acceptable. Considering that bottled food-grade CO2 can have up to 50 (but usually less than that) ppm of residual O2 you wouldn't be able to reach residual levels of O2 lower than that anyway, so there is really no point in purging so extensively.
true. thats just idiocy. but that is the extreme example. and that's going further than i'm talking about. since you're talking about a stainless vessel, how do you know you're not getting any foaming ? you cant see it.
im not talking about degassing anything, thats crazy talk. and you dont need a volcano to jump out of the fermenter to wind up with a big ass ring of hop material on the sides of your tank, or even the upper dome if you had a baby gusher. with a clear plastic or glass fermenter, you can see breakout occur even when its not catastrophic. just a big thick hop/bubble/wort layer on top of fermenter. yes, granted, that's at ambient pressure. but the point is that the hops themselves will create a little breakout as they absorb the wort but not the dissolved gas, and then as they do their thing expanding and breaking apart.
your manometer statement is making me think about this more, not sure how that squares. but what i can tell you is that in a semi-transparent vessel like hdpe you can see the thick bubbly hop layer on the top. then as they absorb the wort and eventually sink you're left with the ring of hops on the fermenter walls. that is waste. even if its not as bad as the waste from a volcano blowout. sure, its always going to happen to some extent, but the bigger this hop/bubble layer is the more gets stuck on the walls.
as to your manometer readings..... perhaps because co2 is in this wort-hop-bubble matrix its not affecting headpsace pressure? or maybe at higher pressures the effect is small? the hdpe vessel we watched only held about 4-5psi. perhaps there is a higher pressure required to keep bubbles from forming and making the hop-bubble layer?
dunno.
hence my question about process.
You can through a 3" sight glass.
The rotary vane vacuum pump I use has a ball style shutoff valve on its intake. This valve is opened right before the pump is turned on and closed right before the pump is turned off. The pressure on the line that feeds into the pump is never under vacuum while the shutoff valve is open and the pump is turned off. I'm not sure how oil vapors are going to migrate upstream into my dry hopping equipment. In do so I think they would be breaking the 2nd law of thermodynamics. I guess there would be some possibility of some of the oil vapors from the pumps output condensing from the air in the room onto the interior surfaces of the main 3" TC valve. This would occur after the dry hop process has been completed and the spool is removed to be replaced with the top cap. I usually keep a couple paper coffee filters attached to the pumps output to capture the majority of the oil mist/fog that the pump produces. The better option would probably be running the exhaust of the pump through some tubing and out a window.
0.8 bar vacuum is only around 20%. Using the calculations above I think you would have to run the evacuation, purge, vent process 8 times at 15psig just to get under 30 ppm of O2. You are only saving yourself 5 purge cycles at 15psig to achieve the same result as you would not using a vacuum pump at all. What you save in CO2 seem like it would be wasted in time. I only evacuate once for one minute, then purge twice at 15 psig, then balance the pressures before the hop drop.
