Total Package Oxygen 101 – TPO Calculation

For the past several posts we’ve been talking about calculating TPO using dissolved oxygen values on shaken packages. Now let’s go for it, and talk about the calculation itself.

The standard reference TPO calculation in use today first appeared in a 1985 article in Brauwelt. There’s a lot of math behind this, so if you want to really understand all of the parameters then it’s well worth looking up: C. Vilachá and K. Uhlig, “The Measurement of Low Levels of Oxygen in Bottled Beer,” Brauwelt International (Volume 1, 1985), 70-77. In the meantime, let’s dissect the calculation and then talk about how you can get an excellent approximation of the TPO using your dO2 measurement. Here’s the equation:

m (t) = total oxygen in mg

X = oxygen content of the beer mg/L (or ppm dO2)

T = Temperature degrees K

The table below shows the dO2/TPO Ratio multiplier you need to apply to your dO2 to get your TPO.  As you will see in the table, the multiplier or dO2/TPO Ratio is very dependent upon the package temperature and headspace volume.

Package Type

Liquid

Volume (mL)

Headspace

Volume (mL)

Temperature

Degrees C

 dO2/TPO Ratio
12 Oz.

355

17

5

2.1

12 Oz.

355

22

5

2.4

12 Oz.

355

17

20

2.4

12 Oz.

355

22

20

2.9

22 Oz.

651

25

5

1.9

22 Oz.

651

25

20

2.2

22 Oz.

651

35

5

2.2

22 Oz.

651

35

20

2.6

So let’s pick an example from the above table, and do our calculation. If you have a 12 oz. package with a 17 mL headspace and you are measuring at 5 degrees C, multiply your dO2 by the ratio of 2.1 to get your TPO. We’re using 100 ppb  (0.100 ppm) in this example.

dO2 x  dO2/TPO ratio = TPO     such that     0.100 mg/L x 2.1 = 0.210 ppm TPO

My final thought is that if you have tight TPO specifications or really want to track everything back to a LIMS system, then a TPO analyzer is the right choice. Otherwise, using a calculator in an excel spreadsheet will get you an equally accurate concentration if you know which parameters are important.

If you would like a copy of a TPO calculator that works in excel, leave a comment and I will email one to you.

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48 responses

  1. I would be very interested in the Excel calculator if you could send a copy. My brewery is putting together TPO testing and there is a surprising amount of information on the subject that falls somewhere between lore and BS, so these posts are quite helpful. Thanks a lot.

  2. I would be thrilled if you would share your excel sheet for TPO. This method of calculating TPO seems far superior then our current caustic shake method for determining “air”. Thank you for posting this information.

  3. Thank you very much for all information you share. I’d like to get a copy of your excel spreadsheet if possible. Cheers!

  4. Hi Chaz, I really like the way you’re talking about DO, TPO,… in such a practical way. I’m very intrigued by the TPO calculation: could you please send me an excel-copy of the calculator? Thanks a lot!

  5. Can you send an excel files of this TPO calculation. I have a Hach 3650 instrument that needed TPO calculator. Thanks!

  6. Good day Chaz. can you send an excel calculator to my email. I have a Hach instrument that needed the TPO calculator. Thanks!

  7. Hi, I’m new to the brewing industry, so forgive me if the answer to this question is obvious, but…how do you accurately measure the headspace volume?

    • There are two ways to check for HS volume. Cans can be weighed and then and the volume can be calculated from the overflow volume.

      Total Weight – empty can weight = content weight. Content weight X product density = liquid volume. Overflow volume – liquid volume = headspace volume. The overflow volume is provided by the can manufacturer.

      Bottles are easier to estimate. The ASBC method can be used, but for TPO calculation purposes there are simpler ways. The ASBC method involves weighing the contents and bottle and then filling the bottle with water to get the overflow volume, then subtracting the bottle weight from the total weight to get the content weight, multplying that by the density to get the content volume and subtracting it from the water weight.

      What I do is estimate the average HS volume with ten cold beers by taring one on a scale, adding water from a squirt bottle until it’s full and assuming that the water weight is the same as the headspace volume. I then average the ten to look for statistical spread and assume that it is representative of the filler.

      • Hi again Chaz – May I have a copy of your excel spreadsheet? (I tried to construct my own, but must have units wrong or a misplaced parenthesis.) Thanks!

  8. Hi!Can you please send me a copy of the calculator?I have 1 question also please!Can I calculate the foreign gas content with this method?We still use the old method with the KOH and we want to move to this one!

  9. If I understand correctly, O2 readings from shaken packages don’t have much comparative value, because the dissolved O2 reading depends on the temperature and headspace of each respective sample. Or am I missing something? I guess I don’t really understand what TPO means. If my TPO is 0.210ppm, that parts per million- of what? Is it on a volumetric basis, assuming the O2 was evenly distributed between the liquid and the headspace?
    And yes, I would love a copy of the spreadsheet. You Blog is fantastic!
    Cullen Dwyer
    QA Manager, Wachusett Brewing Co,

  10. Hi there,

    Have a TPO calculator, but I would really like to see the differences between the one we have compared to this model. Question: Would the theroy behind this also work the same for Packaged Cider?

  11. Chaz,

    I have really enjoyed your blog posts. Thank you for being so transparent with your knowledge. We employ both a 3650 and 3625 in our QA. I would like to review your TPO calculator if you are still able to send it our way.

  12. Hello-

    If its still available, I’d like a copy of the excel calculator. I tried my hand at making my own, but for some reason could not use that equation to match the sample numbers you’ve published in your examples. Thanks for the help!

  13. i would like the TPO excel calculator, im working in a brewery and we have discussions about the low parameters measured in our bottles, about 25 – 30 ppb and our TPO is 20 ppb less than our dissolved O2. Considering we are using antioxidant. is it possible..??

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