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Old 10-25-2012, 03:59 AM   #51
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Here is the data from this batch. One procedural differences to highlight ... This time I switched to a wider bottling wand which left more headspace than last time (probably double the headspace as last time, about 2"). I'll probably go back to the narrower bottling wand b/c I don't like that much headspace.

Now some comments on the data. Near the beginning there is about 12 hours of missing data where the monitor crapped out. Think I know what happened and how to avoid it next time.

The initial pressure rise was really fast.

I don't really know why, but the pressures never really reached where I would have expected. I doubt it can be attributed to the increased head space. If the data is right then the CO2 in this bottle is about 1.5 volumes. I'll say that other bottles from this batch are properly carb'ed - definitely more than 1.5 volumes. I haven't cracked the monitoring bottle yet.

I do see some similar artifacts as last time (besides the 24 hour cycle) - looks like overshoot, then oscillations settling to a mean.

I'll also mention that today we did not have the AC on and local outdoor temps reached 80. That's the probable reason for the last spike.

Any thoughts on what I should do differently next time? I may have to put the bottle in my fermentation chamber to keep the temp more constant. This water bath was not a temp controlled bath - just more thermal mass to try to slow the swings and apparently wasn't very effective. I'll also see if I can get a temp recording. Would be cool to have a gravity reading too, but I can't imagine how to do that.


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Old 10-25-2012, 07:29 PM   #52
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That looks like Logger Pro, what sensor are you using to read the pressure?


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Old 10-25-2012, 10:43 PM   #53
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I think having an RTD in a thermowell inside the beer and logging those temps would be ideal. One thing I suspected could be happening is that your bottle seal, or the bulkhead you put in is only capable of holding 10 psi and any more than that, it tweaks the seal letting some gas escape. That would explain the oscillation if it is not directly correlated to beers temps. I don't know how exothermic this mild fermentation is.
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Old 10-30-2012, 11:45 PM   #54
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Originally Posted by ZackN View Post
That looks like Logger Pro, what sensor are you using to read the pressure?
The sensor is off the shelf. It's a Dwyer 628CR with 0-50 PSI range. The logger is something I built with spare parts.
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Old 10-31-2012, 12:13 AM   #55
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One thing I suspected could be happening is that your bottle seal, or the bulkhead you put in is only capable of holding 10 psi and any more than that, it tweaks the seal letting some gas escape. That would explain the oscillation if it is not directly correlated to beers temps.
I thought about this some more and tried another experiment. I used a couple of alka seltzer tablets and a small amount of water in the bottle to build pressure and test for leaks. The small amount of water was so that I wouldn't see much effect from CO2 being lost/dissolved back into the water. Some background: The cap I made uses a kork-n-seal resealable cap (see http://www.sha.org/bottle/closures.htm about midway down for a picture). I picked up some of these that were in excellent unused condition. I took this route b/c I wanted to use a glass bottle and a re-usable cap. Anyway, when I ran the leak experiment, it didn't seem like the pressure went as high as I would have predicted. When I picked up the bottle and placed pressure on the lever, I heard a hiss. I ran the experiment again and overnight the pressure dropped from about 15 PSI to 4 PSI. Definitely a leak existed. I examined the rubber seal and found that it was pretty compressed and had a slight amount of residue underneath it. I think it was the original seal in the bottle cap (prob circa 1960!). I replaced it with a new hose washer which is a slight bit thicker and made with more modern material. The lever now resists more and snaps into place. I started another experiment on this new cap and it's held 22 PSI for over 24 hours now.

I suspect the leak developed on the second batch and got even worse when I tried these leak experiments. I'm not sure about the first dataset. It seems like a leak would be more intermittent and faster. But anyway, no way telling until I run the priming experiment again. This time I'll pre-test the cap to 30 PSI and I might just switch to a plastic bottle/screwtop.

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I think having an RTD in a thermowell inside the beer and logging those temps would be ideal.
That shouldn't be too hard. But I would probably change to a PET bottle if the sensor had to be in the beer. However, I think it would be good enough to tape a sensor to the outside of the bottle and insulate it.

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I don't know how exothermic this mild fermentation is.
I would guess it's not very exothermic. I'd be surprised if it raised the temp by more than 1F.
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Old 10-31-2012, 03:21 AM   #56
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I did go on weather underground to get external temps for my area from that timeframe, but my recollection is that when I graphed them together with pressure there wasn't any obvious correlation. However, I agree that other phenomena (drafts, etc) could have contributed. Ultimately I need to measure ambient temps - and maybe do a better job controlling them.
I guess I'm not really sure what I did back then ... but, I went back and graphed average outdoor temps vs pressure and there does appear to be some correlation. I still want to run the experiment with more temp control and recording just to see if this is all due to temps. I also filtered out the signal with 24 hr period in this data.
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Old 11-14-2012, 02:40 AM   #57
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Disagree. A bottle of sealed soda has co2 at equilibrium. Shaking does not pull co2 out of solution because it can't. The partial pressure in the headspace and the newly formed bubbles already matches that of the dissolved co2. The reason it gushes after shaking is that the bubbles create nucleation point similar to mentos in diet coke.
Shaking can pull it out of solution because nucleation (from energy input spent shaking) IS causing CO2 to escape from the liquid (evidenced by the bottle hardening) and it is not being replaced back into solution at the same rate, and therefore it is no longer in a state of equilibrium. Equilibrium doesn't imply that two things are equal, it just means that reactions going both directions are happening at the same rate. After shaking the bottle and causing CO2 to escape from solution, there is excess CO2 in the headspace above the liquid due to the energy put into shaking the bottle, and according to Le Chatelier's Principle, after the shaking has stopped (no more energy input on reactant's side), excess products on one side will cause the reaction to shift so that more reactants are created. Basically, CO2 will begin dissolving faster than it is escaping the liquid. But it still takes time for equilibrium to be established again. CO2 is CONSTANTLY seeping out of the liquid and being absorbed. In equilibrium, these rates are the same. When you put in energy (such as shaking), you are disrupting the equilibrium. This principle also explains the effect of temperature, because the K value changes with it.

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Old 11-16-2012, 06:29 PM   #58
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Shaking can pull it out of solution because nucleation (from energy input spent shaking) IS causing CO2 to escape from the liquid (evidenced by the bottle hardening) and it is not being replaced back into e and causing CO2 to escape from solution, there is excess CO2 in the headspace above the liquid due to the energy put into shaking the bottle, and according to Le Chatelier's Principle, after the shaking has stopped (no more energy input on reactant's side), excess products on one side will cause the reaction to shift so that more reactants are created. Basically, CO2 will begin dissosolution at the same rate, and therefore it is no longer in a state of equilibrium. Equilibrium doesn't imply that two things are equal, it just means that reactions going both directions are happening at the same rate. After shaking the bottllving faster than it is escaping the liquid. But it still takes time for equilibrium to be established again. CO2 is CONSTANTLY seeping out of the liquid and being absorbed. In equilibrium, these rates are the same. When you put in energy (such as shaking), you are disrupting the equilibrium. This principle also explains the effect of temperature, because the K value changes with it.

EDIT: here's a picture

I'm not biting on this just yet. Have you ever put a pressure gauge on a sealed carbonated container, noted the pressure at stasis and then noted a pressure increase after shaking? If you haven't but know of a video or paper where it has been documented let me know.

http://www.phys.csuchico.edu/kagan/profdev/soda.pdf

I don't know why you would suggest that shaking in a closed system disrupts equilibrium. Le Châtelier's Principle requires that you change something like temperature, pressure or concentration. Shaking does none of this.
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Old 01-31-2013, 04:05 AM   #59
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OK, trial 3 is finally done. It turned out to be a pretty tasty beer too! (afterall, this really is still about making beer) It started as a Goose Island Mild Winter clone, but I decided to add a little more rye than normally recommended. I tastes nice, but I know I wouldn't add any more rye than I did.

Anyway about the experiment. I built an entirely new cap/bulkhead to try to eliminate the leak issue:

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I pressure tested it to 49 PSI for about 2 days and it didn't appear to leak at all:

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The priming was carried out in my fermentation chamber at around 70 F for 3 weeks. It does look like the pressure built to a plateau of 39 PSI and then diminished to settle at 35 PSI. The priming sugar amount should have put this at 2 volumes. At 72 F (as measured) that should have make a pressure of about 23 PSI at equilibrium. This is obviously well above that.

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Old 01-31-2013, 04:10 AM   #60
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very cool


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