Oxygen reduction in distilled water

[mr.jay]

I hate it when "geek sessions" lead you down a road to nowhere. I had an interesting conversation with another brewer the other night that has me thinking. Disclaimer: I don't subscribe to the practice of diluting my final product with water, for several reasons. That being said, I asked him how he keeps up with his pilsner production with such little space. This fellow brews to a higher gravity, adds a boatload of dextrine malts, and dilutes his final product with H20. I asked him how he removed the oxygen from the water. I thought maybe he boiled it, and ran it through his heat exchanger into his brite tank. No. He adds city water to his brite tank, and bubbles CO2 through a stone for several hours. His theory is (here we go again with the theories) the CO2 will essensially "lift" the oxygen out of the solution, and that there is some kind of bonding that takes place (similar to Carbonic acid neutralizing Hydroxide). He drew this out on a napkin for me, and I laughed. The idea of doing this seems absurd. I would be more worried about traces of colliform or other bacteria in the water. He was at my house, so I didn't have the opportunity to taste his final product, but his customers seem to love it, and I guess that is what counts. But I was wondering if anybody has any thoughts on this. By the way, for those who responded to my oxygen vs. air thread. Since I switched to 99.9% pure air, there has been a great reduction of dead cells in my cone, and the body seems to have improved on some of my beers. Just a coinquidink? Hmmmm?

[brewery master]

first uv your water through 1 micron carbon cartrage ,cool water to at least 36 f. add co2 at 15 lbs through 6in.by 3/4 .02 stone ,set tank blow off at 13 lbs for 1000 ltre.allow 60 minits your done you see co2 is 6 times heaver than air and six times larger . how much o2 in your well water you may be just add it directly to the beer .the big three in canada have being brewing with a fire hose since 1969 .I tried this last summer made some intresting beers but making it shelf stable is more science. don@ brewerymaster.com cheers don

[dick murton]

It's nothing to do with atomic weight of the differnet gasses, but pure physics. If two pure gasses come into contact with each other, then they disperse to maintain the ratios in each other. So if you bubble CO2 through oxygen saturated water, some of the oxygen will pass into the CO2. If you allow the CO2, with the entrained oxygen to escape, hey presto - you have less oxygen dissolved in the water. Keep doing this with pure CO2, and before long you have virtually oxygen free water. Admittedly some CO2 will also have dissolved in the water, dependant upon the water temperature and system pressure, but this is often not a problem. If it is - use nitrogen instead. Plenty of brewers use nitrogen stripping, and a few use CO2 stripping. Nitrogen is used more frequently becasue it is cheaper to produce, and can often be bought in as a by product of oxygen production, but more simply by haveing a stand alone N2 generation plant - if the requirement is big enough.

Cheers

[Larry Horwitz]

Hey Dick,
had a blast in Seattle. Bubbling CO2 through your water is a very effective way to reduce it's o2 levels. A friend of mine makes all of his DO water this way (checks with orbisphere) and has great success....it just scrubs out the o2.

A small stone in the dose tank of your DE filter will do wonders for the DO pickup if you dose with water.

[dick murton]

Thanks. It's nice to get positive reply once in a while

Cheers

[sbradt]

Plenty of brewers use nitrogen stripping, and a few use CO2 stripping. Nitrogen is used more frequently becasue it is cheaper to produce, and can often be bought in as a by product of oxygen production, but more simply by haveing a stand alone N2 generation plant - if the requirement is big enough.

Does anyone have information regarding the amount of N2 required to strip a given volume of water? Our water supply runs at about 10ppm DO. If I want to drop 30 Bbls of water from 10ppm to 0.1ppm, assuming standard Temp & pressure, is there a way to approximate the amount of N2 (or CO2 for that matter) that would be required for stripping? I'd like this information to make some cost and volume estimates on stripping gasses.

Is the stripping more effective with some top pressure?

Thanks

[KWLSD]

I recall doing some empirical work on this in a brewery I worked at a good few years ago. The conclusion we arrived at was that we needed to maintain a nitrogen level of 21mg/l to bring dissolved oxygen down to <0.10ppm.

However, we didn't look at the efficiency of the process, ie. the amount of N2 we were using to get to 21mg/l

Oh well, that's part of the way to an answer...

[dick murton]

It is easier to strip out oxygen if the water is ambient or even warm than when it is cold. This is a simple matter of gas solubility - oxygen being far more soluble at low temperatures than high. Because of this I wouldn't like to even suggest a figure for gas stripping as so much depends on the conditions, temperature, surface area etc.

However, to give some sort of indication of the difference, whilst commissioning a brewery (in Tunisia - during Ramadan with a Muslim workforce - don't worry there are also loads of wineries, and at least some of them drink alcohol, at least outside religious holidays etc) - if the water was prechilled to 2 deg C, then it would take about 6 hours of gas purging. If at ambient, say 20 C, then it would come down in less than an hour. We happened to use CO2, but pure nitrogen works just in the same way, and may be cheaper if you have to buy in pure gas. We had about 1 bar top pressure on the tank, but this was, as much as anything becuase they wanted to partially carbonate the water.

We used to recirculate the water through the sprayball, injecting CO2 into the line between the pump and the sprayball. For anyone bigger, have a look out for the IsoMix system - basically a fully immersed Toftejorg high pressure cleaning head instead of the sprayball above the water surface. Same basic concept but claimed to be more efficient

Happy & prosperous new Year


Cheers

[sbradt]

Following on Dick's comments, I tried an experiment to begin getting some idea as to the amounts of N2 or CO2 needed to reduce the DO level in water. I thought I'd post the results for future use.

I put 25 Bbls of cold water (45F - our current incoming water temp) into a bright tank and used the carbonating stone to sparge with CO2. The beginning DO was about 9.5 ppm. I ran the CO2 out of the regulator at 30 psig. There was no top pressure on the tank. There was a pretty dramatic drop in the first hour and then it slowed down a bit. It took about 4.5 hours to lower the DO to <0.1 ppm. In the process I consumed just over 400 cu ft of CO2. The water, needless to say was a bit fizzy and sharp with the taste of carbonic acid.

I repeated the experiment with N2 and found very similar results in terms of the amount of gas required and the time required. I was not quite able to get down to the same level of DO (stopped at 0.34 ppm) because my gas cylinder ran out but based on the way the process was progressing, it seems like the results were going to be very similar. The big difference was that the N2 stripping resulted in a very flavor neutral water.

One interesting side observation was that the ∆p across the stone was significantly lower with the N2 than with the CO2, presumably due to the fact that N2 is less dense?

I realize that there are probably more efficient ways to perform this operation but this gave me a good start.

Now - the question. I had been considering using a spare tank we have as a de-aeration tank. It would need to be tied into our glycol system because I want to use chilled water for filter setup, bottling line setup and bottle rinsing. It would also require a pump of some sort to deliver the water. Then it dawned on me that our cold liquor tank already has all of those things along with a recirculation loop (to a glycol heat-x for cooling) that could easily be fitted with a stone. It is oversized and we aren't likely to be brewing and bottling concurrently in the near future anyway). That raises the question - is there any problem with N2 stripping my cold liquor? Like many systems, my chilled water is used to chill wort via a heat exchanger and the resultant hot water is reclaimed to the hot liquor tank for brewing. Due to its temperature, hot liquor has a pretty low DO content anyway so I'm assuming that it is not problematic to start with de-aerated water. The only issue I can see is if there is a significant dissolved N2 content(?) in the O2 stripped water and if that has a potential impact on its performance as brewing water.

Any comments?

[KWLSD]

Hi Steve,

If you're raising your water temperature on the wort cooler, then you'll already be reducing the N2 content at that stage. I'd guess that most of it will 'escape' when it enters the hot liquor tank so no, I don't think you'll have any issues.

Don't forget that the water you're using already in that process will have an N2 level if it is being drawn from a mains supply, since most of these are pretty-much air-saturated anyway (which it looks to be, from the DO2 of 9.5ppm incoming).

You might have to increase your oxygenation to ensure the correct level for fermentation though, as you'll be starting from a lower point.

Regards,
Tim