Sulfite Strip Test

[Bilsch]

Very interesting read !
Thanks so much for posting your test results. I guess I missed this when it was first posted.

[Weizenberg]

[Nick_D]

[lupulus]

Can anyone in the forum write as to the validity of the sulfite strips to measure sulfite?
The Quantofix instructions make a note of reducing media altering the results, and as malt has polyphenols (and other reducing substances if AA or BTB are also added to mash/ boil), I wonder if somebody has tried to control the measurements.

A simple way to test the validity of the strips would be to do two separate small mashes. In one you add the SMB first and then the malt, in the other you add the malt, give it 10 min and then add the SMB. If your hypothesis is correct and most or all the malt polyphenols oxidize instantaneously, adding 100ppm of SMB to the oxidized mash should not consume sulfites and the reading should be 100ppm higher vs before the SMB was added.
On the other hand, the mash in which the SMB was added first should show a consumption of the sulfites after the malt was added.

Thoughts?

BTW - Another question is whether anyone has used the Indigo strips (the usage is different so may be their method is as well).

[Weizenberg]

It's certainly an interesting experiment to perform . I'd be all for it!

[Techbrau]

A few caveats:

100 mg/l SMB will add at most 76 ppm sulfur compounds as it is 24% by weight sodium. Some of the sulfur compounds may also quickly off gas as SO2.

Without knowing the stoichiometry of the redox reactions involving the phenols, along with how many exist in the mash, you won't know what kind of relative difference to look for in the sulfite readings. George Fix hypothesized that 1 ppm dissolved oxygen is all it takes to do significant damage, which has been consistent with our observations. So it could be that the reducing power of the phenolics is very low, perhaps only a few ppm. Scavenging 1 ppm of DO takes 5 ppm sulfite, so it's possible that you may only get a 5 ppm difference in the sulfite concentrations between the mashes, which is way below the resolution of the test strips.

You'd need to use a much higher resolution measurement technique, not to mention performing this all in a completely oxygen-free environment because you don't want the atmosphere messing with your measurements. Atmospheric oxygen is going to be continuously diffusing into any liquid whose DO concentration is lower than the saturation limit set by the partial pressure of oxygen in the atmosphere, which isn't taken into account here. Of course, if you do this all under inert gas then the partial pressure of the oxygen will be zero, pulling any DO from the mashes out of solution. So actually you'd need to find a way to perform this experiment in tightly closed vessels with zero headspace.

[lupulus]

@Weizenberg - Thanks so much

@Techbrau
The theoretical maximal contribution of SMB if fully converted to sulfate is 101ppm not 76ppm

INFORMATION NEEDED
Sodium metabisulfite molecular mass 190.107 g/mol
Sulfur molecular mass 32.065 g/mol
Sodium metabisulfite chemical formula Na2O5S2
Sulfate molecular mass 96.060 g/mol
Sulfate chemical formula SO4
Given the information above
190.107 g SMB has 2 * 32.065 g of sulfur
Using the info above 100 g of SMB has 33.734 g of sulfur
Calculation is 100 * 2 * 32.065 / 190.107
96.06 g sulfate has 32.065 g of sulfur
33.734 g of sulfur fully converted to sulfate gives 101.0588774 g of sulfate
Calculation is 33.734 *96.06/ 32.065

@Techbrau
I do not disagree at all with what you are saying, but the question I am trying to answer is whether reducing substances in the malt affect the reading of the strips (as stated in the strips brochure). If there is a significant amount of reducing substances in the malt that get oxidized by the free O2 radicals, then adding the SMB after adding the malt would result in a significantly darker strip (more sulfite) vs adding the SMB first and then the malt.
Indeed, quantification will take a much more controlled experiment.

[Techbrau]

The sulfite strips measure sulfite, not sulfate. So you are not going to get more than 76 ppm on your reading.

The question pertaining to the malt antioxidants is how much of them exists. They could be very fast acting but few in number - this is consistent with the observation that it only takes 1-3 mg/l oxygen to destroy their flavor. If this is the case then their reducing power is equivalent to only 5-15 ppm sulfite, so you will need to be able to reliably measure sulfite concentration differences smaller than that.

All that said its entirely possible that you'll measure a much larger difference than 5-15 ppm. Which would suggest that our hypothesis is correct. My point is just cautionary in the sense that an experiment which doesn't show a significant color difference on the test strips does not necessarily disprove the theory for the reasons I outlined.

[lupulus]

Thanks for writing back.
Apologies. I misread your statement to mean literally the maximum amount of sulfur compounds, which is 101 ppm if all SMB is converted to sulfate. Your are correct in that the maximum amount of sulfites in any of their variations should not significantly differ from 76 ppm.

I may have not explained my point well enough.
Ancient Abbey degassed the water and despite this degassing and theoretically low O2,it appears that immediately at mash-in 50 to 75 ppm of Sulfites were consumed per the strips (see his experiment).
This is not what the LODO theory predicts, which is that in a tight system one would gradually consume no more than 10-20 ppm if all goes well.
If one consumes 50-75 ppm just at dough-in, then 100 ppm SMB dose should be a minimum, but is not.
An alternative explanation for this low reading after dough-in is that reducing substances in the malt lowered the reading (as indicated in the strips instructions).
Does my question make sense now?
Cheers,

[Owenbräu]

The experiment was run at 100mg/L SMB, which should be a reading of ~76 ppm sulfite. The measurement after doughin in looks in between 25-50 mg/l. I tried to lay the strip on the color if it was dead on, and in the gap if I though it was between readings. That reading could have been as low as 25 mg/l and as high as 50 mg/l. So, yeah the initial reduction was in the 25-50mg/l range. I will say, this was done as I was building my system, i.e., before replacing all my fittings with TC, pre-mash cap, etc. I don't think anyone is seeing a 50ppm drop anymore, and are definitely on the low end of sulfite consumption, consistent with Narziss.