Well... there are 1,000mg in a kilogram... there are 1,000ml in a Liter...
Does that help?
I have a question for you all regarding oxygenation of wort. I have a friend who works in a brewery in which they oxygenate inline from the wort chiller to the fermenter with pure oxygen (which seems to be the standard practice nowadays) . He said that on average, for standard gravity worts (10 to 12 plato), they use 8 litters of O2 per barrel of wort, which then allows them to calculate the flow rate in litters per minute from their oxygen source.
total barrels wort * 8 l/bbl O2 = total litters of O2 needed
total litters O2 / knockout time (in minutes) = flow rate of O2 in liters per minute
My question is this: with most professional brewing texts out there saying that you need 8-10ppm (or 8-10 mg/l) of O2 total (for standard gravity worts), how does one get from mg/l to l/bbl? I've attempted to do all of the calculations numerous times, but just can't seem to figure out how to get from mg/l O2 to litters O2. On top of that I still can't figure out how they figured out how to use a metric measurement in conjunction with a US barrel.
Any help/explanation (or even a point in the right direction as far as a text/lecture) would be greatly useful and much appreciated!
Well... there are 1,000mg in a kilogram... there are 1,000ml in a Liter...
Does that help?
Grassroots - thank you for your reply!
I'd like to think I understand the metric system, but I guess what still has me confused is that grams/milligrams are measurements of mass, liters/milliliters are measurements of volume, and milligrams per liter is a measurement of concentration so how do you get from one to the other? If oxygen concentration is stated in ppm or mg/l, how can you convert that to a measurement of volume in liters?
Maybe I actually don't know the metric system as well as I thought, haha?
Hey guys, there are 1,000 mg in ONE GRAM. And 1,000 grams in a kilogram. There are 1,000,000 mg in one kg. And one liter of water weighs 1kg. Hence one mg per liter (of water/SG=1.000) is the same as 1ppm. ElJefeweizen, your confusion between a weight measurement and a volume measurement is understandable. But if one liter of water is one kg, the two are interchangeable. Also check numerous other posts about oxygenation. Personally, I'd use air as opposed to oxygen. No real need to measure flow rates with air--at least with standard strength worts. And no chance of "burning" the wort. Good luck!
Phillip Kelm--Palau Brewing Company Manager--
Worldwide Brewery Installations
Those conversions are cool on the water end, and ok approximations on the wort end, but ElJefeweizen is talking about converting a mass of CO2 to a volume of CO2. To convert between the two, you can use the ideal gas law:
Pressure x Volume = Mass x Universal Gas Constant x Temperature / Molar Mass
For O2 and metric units (pressure = Pa, volume = L, mass = mg, temperature = K), the equation becomes:
Pressure x Volume = Mass x 8.314 x Temperature / 32
Rearranging for volume:
Volume = Mass x 8.314 x Temperature / 32 / Pressure
If you plug in 8-10 mg/bbl instead of a straight mg value, your result will be in L/bbl. Unfortunately, there a couple of issues. First, all of the oxygen you inject won't go into solution. Second, you'll need to figure out if your flowmeter reports as-is conditions or the gas flow equivalent at standard temperature and pressure. If it reports as-is conditions, you'll need to know the pressure and temperature of your gas at the flowmeter. That's not easy to figure out. If it reports STP conditions, you'll need to know how your manufacturer defines STP (I believe most folks recognize it as 273.15 K and 101325 Pa, but it's not universal).
The bottom line is that you'll probably need access to a dissolved oxygen meter, or somebody with one, to really know what's going on with your wort and how to adjust your flowrates/times. In either case, make sure your wort is tested before it comes into contact with your yeast.
Last edited by jwalts; 04-28-2011 at 10:34 PM.
Jwalts - thank you - everything you have said makes perfect sense especially in terms of the ideal gas law...needless to say I've whipped out my "Chemistry for Dummies" to refresh my brain on that whole concept, haha!
My one question I have for you is that if I plug in "8-10mg/bbl", won't that concentration be much less than 8ppm (mg/l)? there are a little over 117 litres in a barrel (31 gallons) correct? I guess I'm just confused as far as 8-10mg/bbl being the proper concentration...
Thank you all again and cheers!
Yeah, you're right. Oops! I should've said something like "multiply 8-10 mg/L by your beer volume to get the mass value to plug into the equation."
Ha! You are exactly right. In my post brew day stupor, I misspoke! Thanks gitchegumee... sigh.
Thank you guys all very much for your input! As a second part of my question, have any of you worked, or do you now work with a pilot rig/smaller system in which you oxygenate inline? When dealing with much smaller systems I'm just curious to know if any of you have gone to the trouble of doing these same types of equations on a 5-10 minute knockout (which would require a flow rate much, much lower than what you'd see in a 15bbl or larger system).
In preparation for brew school (I'm applying to both the ABG as well as UC Davis - we'll see which I manage to get into first, haha!), I'm looking into a BrewMagic (or a comparable pilot-type rig) w/ Chill Wizard to help me along the way as I'd like to be able to replicate the entire process as close as possible to what I will be doing in a professional brew house.
Anyway, thank you all again for your insight, and may I say I'm so thankful for a forum such as this where pros and aspiring pros alike can come and share their knowledge and experience with each other (and that you're all willing to do so)!
Oh, and I wanted to go through the equation to make sure I'm going it right...here goes:
This will all be assuming I'm shooting for 8ppm (8mg/l) of oxygen (and also assuming STP).
1 bbl = 117.35 liters
117.35 * 8 = 938.8 mg/l O2 total
V = 938.8 * 8.314 * 273.15 / 32 / 101325
V = 0.65753324 L O2 per barrel
Ironically I've gotten this number a couple of other times in attempting this calculation so it must be right?
The only thing that seems strange to me is that my friend said in his brew house that he's using 8L O2/bbl which is WAY more than this. Maybe their equations are much different (especially being that we're in Denver so the pressure is NOT going to be at STP, and also perhaps they're accounting for the knockout temperature of the wort rather than the 273.15K at STP? It would make sense that at a higher pressure and temperature, (as well as if they also bump up the number to account for reduced oxygen solubility) that the volume could increase substantially, but we're talking about a 1200% increase at 8L/bbl!
If I can add a few notes to people reading this looking for the correct numbers for their fermentations...
Having calculated all this stuff, note that it refers to the amount of oxygen dissolved in the wort, which is not necessarily the same as the amount of oxygen added to the wort...
Beyond that, every yeast, pitching rate, and condition of the yeast and fermentation affect their corresponding optimum numbers. I have found that the textbooks have useful numbers merely to start with.
My best results came from first accurately gauging the oxygen flow, and then scrutinizing the yeast performance under different aeration rates. Each culture can have its own needs, and the age of the culture or your cropping procedure may seriously affect your yeast's requirements or preferences, which could be far different than can be found in random textbooks that have numbers generated from situations different from yours.
100% with Moonlight on this one. The different efficiencies of various setups to convert delivered oxygen to dissolved oxygen combined with the dramatically different oxygen needs of yeast strains makes this much more than a calculation issue. Observation and record keeping are the most critical elements to establishing proper aeration rates. We have two house strains and one I think could pull off a fermentation without aeration (not that I'd try) and the other will not budge unless it's pretty well blasted w/ O2. Unfortunately you usually learn that stuff the hard way.
Evolution Craft Brewing Company
Totally with you both on the differences between different strains, as well as differences in temperature/pressure...the strain in question that my buddy was referring to is Wyeast's 2565 Kolsch (for their house kolsch), which could also lead to a big difference in necessary O2 levels.
But still, do you guys think that 8l/bbl up from .65l/bbl is a bit of a stretch?
And again, I realize this is all based on system, type of stone, wort flow rate, temperature, pressure, etc, etc, etc...but a 1200% to me just seems like it might be a bit much. Maybe I just need to corral my buddy down and feed him pints until he talks, haha!
And PS, does that also mean that my calculations were correct, haha?
Also wanted to mention as a footnote, that in all of my posts I have meant to say liters, NOT litters. I'm quite upset at the spell check on my text program right now, lol (although you'd think liters would be a word it would have in it's vocabulary?)...
I may be dumb, but I'm not THAT dumb (hopefully)!
ElJefeweizen, your calculations match mine. That said, it wouldn't surprise me if it takes 8 L/bbl from the oxygen tank to achieve ~0.7 L/bbl of dissolved oxygen in the wort. I wouldn't put any stock in the calculations until you test the dissolved oxygen level of your wort. At that point, you'll be able to apply a fudge factor to the calculations to estimate the right amount of oxygen for a given beer.