SO2 test: aeration time affects reading?

[sremick]

So I'm still getting to know my Morewinemaking SO2 kit. I've run about 4 tests so far on different batches. I've also stocked up on extra chemicals, although the only extras I've had to dip into so far is the phosphoric acid (25%).

I have concerns about the aeration time and how it affects results. The instructions suggest that 10-15 mins is sufficient to guarantee endpoint to the reaction, however it seemed to me that there could be a lot of variability in bubble rate, depth of the tubes in the sample and reagent, etc. So I decided to run one test longer on the last two tests to see what happens. Math at the end suggested over 200 ppm SO2! Ran another batch even longer (kit, so the only K-Meta is that which was added from the kit) and math suggested free SO2 over 400 ppm.

What's going on here? Does some other process take place when the aeration goes past 15 mins that could be messing up the results?

 

[stickman]

There are a few issues to be aware of, anything that causes wine to be carried over into the peroxide trap can cause a high side error, for example if the aeration rate is too high, excessive violent bubbling or foam, mist carry over etc. Sample should be degassed as co2 can cause a high side error. Volatile acidity can also cause a high side error, you can run a blank by adding several drops of hydrogen peroxide to your wine sample and run the test as directed, the result from the blank should be close to zero, but, if not, the blank results can be subtracted from the normal test run.

 

[sremick]

anything that causes wine to be carried over into the peroxide trap can cause a high side error, for example if the aeration rate is too high, excessive violent bubbling or foam, mist carry over etc.

That one we can rule out. The inlet on the first flask is way up at the stopper and the bubbling never went anywhere near that high (I went with a slow bubble to keep bubble size small and contact at a maximum).

Sample should be degassed as co2 can cause a high side error.

Both active degassing and time on these samples can rule that out too.

Volatile acidity can also cause a high side error, you can run a blank by adding several drops of hydrogen peroxide to your wine sample and run the test as directed, the result from the blank should be close to zero, but, if not, the blank results can be subtracted from the normal test run.

That's interesting, I'll have to try that. I also want to try two tests on the same wine with nothing different than aeration time. Would "volatile acidity" skew the results regardless of aeration time?