How Much O2 is Enough? (You can thank Dutch for this post)

[msjulian]

There is just something about brewing beer as a hobby that is so fulfilling! Where else can you go from doing metal work on a stainless boil kettle for a fellow brewer in the afternoon and then stay up till midnight researching chemistry? All for the quest of a great pint of brew...

Thanks to the OVHA supply house (Dutch) I now have an O2 tank with a flow meter. This got me wondering how much O2 do I really need?

My old method was to crank open the valve on the little red welding tank from Lowes full bore and let it eat for 60 sec pushing through a .5 micro stone. Come to find out I may have been over doing it (by a lot).

It appears that for 5.5 gallon (20.82 liters) I only need approximately .119 liters of oxygen to get approximately 8 - 10 ppm O2. That would mean if I ran the flow @ .1 L/min (not 1 L/min) for 72 sec I would end up with .119 liters of O2. That would be assuming that 100% of the oxygen goes in to solution. Which according to BYO's Mr Wizard is not a bad assumption if you use a .5 micro stone at the bottom of the fermenter. But let's just say worst case you only get 50% in to solution. I would still only need to run the flow @ .2 L/min for 72 sec to get the recommended amount of O2 in the wort. It is of my own opinion that the temp and gravity of the wort will play a part in how well the oxygen (much like CO2) goes in to solution.

It's not that I am trying to brew the "perfect beer" here. It's more about conserving my resources. If the numbers above are correct I should be able to get around 800 5.5 gallon batches from one of Dutch's oxygen bottles. At my current brew rate that should last me about 4 years. If another byproduct is healthier yeasties in my fermentor it would be a bonus.

I have seen some inexpensive adjustable gas flowmeters on eBay that have a scale from 0-1 L/min graduated in .1 increments. I think I am going to try and pick one up and see how it goes.

Formulas courtesy of "Ask Mr. Wizard" in Jan/Feb 2008 back issue of BYO.

[sirgiovanni]

You have totally disregarded the effects from tilt of the Earth and the speed of the Mily Way travelling through an infinitely expanding universe.

[KennyPurcell]

Basic Brewing Radio recently did a tasting comparing different types of aeration. The experiment was not well executed but the blind tasting and discussion was interesting.

[Chris Norrick]

What does that low rate LOOK like? I assume if it's all going into solution there would be no bubbles breaking on the surface. I always have bubbles breaking. Sometimes even foaming. But I don't have a flow meter so I have no idea the rate.

[msjulian]

The flow meter on the tank I have starts at 2L/min and at that rate I get bubbles making it to the top. From what I have researched, best case is no bubbles to the top if possible as these will most likely be lost to the atmosphere.

This last brew I took the stainless wand that my stone is attached to and slowly stirred the wort while I was aerating so that the bubbles had to fight the circular flow of the wort to get to the top. By doing this it seemed that the O2 had more contact time and fewer made it to the top. Not real sure how much difference all this really makes but it sure gives me something to tinker with. And I am ALL about the tinkering.

[Dutch]

If you have a flow meter then I have seen good aeration at 2LPM for 1 minute.
I could probably translate that eventually to PSI but it would depend on the stone and tubing used [as there really is no static pressure].
I don't think you would get any flow at very low pressure levels.
In either event with the very small quantities of O2 used [and for the fact that we most likely will not pay for gas refills] some bubbles to the top is not that bad considering we will get about 4000 gallons of beer from one charged bottle of 167 liters?

[msjulian]

The only thing that I have been able to read about over oxygenating the wort is that levels higher than 8 mg/L can cause oxidative damage to yeast cells. At 2L/min it is up close to 50 - 60 mg/L. I don't think that the pressure that is behind the 2L/min setting is really pushing that much flow. It is barely bubbling. I think I am going to an inline flowmeter and just see how much is getting pumped in. I think the gauge on the tank is tied somewhat to pressure. If you hold your finger over the output the flowmeter number climbs. If it were a true flow reading I would think that it would drop to 0 when you blocked it off.

Again, I don't really know for sure what this is all worth but it sure is fun doing the research and calculations.

For the life of me I can't understand why they don't teach these "real world" examples of chemistry in high school. I would have most likely got an A.

[msjulian]

Found this flowmeter. Adjustable .1 L/min - 1.5 L/min on .1 increments. I think this will tell me what I need to know on the flow when it is restricted by the .5 micron stone.

flowmeter.png