Wine contamination?

[Gwand]

I am making my first juice bucket. It is fresh juice pressed from Montepulciano grapes. MLF went slowly taking about two months to complete. I did not add S02 until after completion of MLF. Then I brought the sulfite level to 35ppm. The S02 level was confirmed with the Vinemetric probe. Two weeks later I measured the sulfite level again; don't ask me why I did this so close to the addition of the sulfite. In any case the sulfite level was now 8ppm. I corrected the level immediately. Does this rapid drop in sulfite level indicate bacterial contamination? While the wine does not taste particularly great at this point it does not taste like vinegar or have any other off flavors. Thanks for your help.

 

[Turock]

Much of your initial sulfite becomes bound to yeast,bacteria,sugars,oxygen and acetaldehyde. And if the bucket came with low sulfite around 20-30 PPM it would not be unusual for the free sulfite level to be very low after your addition. In no way does this mean you have a bacterial infection.

 

[Pumpkinman]

Adjusting SO2 isn't as straight forward as many think it is, this is one of the main reasons that we always recommend testing, and adding based on the test results, I also use the Vinmetrica, it is a life saver.
The reason that the SO2 level changed so quickly is due to Binding, the following was taken from MoreWine, I couldn't have said it any clearer then they have:
Due to the complex way sulfite additions interact with the various chemical compounds and solids naturally present in our wines, the amount of free sulfite remaining in the wine after we make an addition often falls short of our calculated goal. This loss is coming from a binding phenomenon which needs to be taken into account and corrected for or our wines risk not being protected in spite of us making sulfur additions.

I urge everyone to take a few minutes and read the entire article: http://morewinemaking.com/public/pdf/so2.pdf.

 

[Gwand]

Adjusting SO2 isn't as straight forward as many think it is, this is one of the main reasons that we always recommend testing, and adding based on the test results, I also use the Vinmetrica, it is a life saver.
The reason that the SO2 level changed so quickly is due to Binding, the following was taken from MoreWine, I couldn't have said it any clearer then they have:
Due to the complex way sulfite additions interact with the various chemical compounds and solids naturally present in our wines, the amount of free sulfite remaining in the wine after we make an addition often falls short of our calculated goal. This loss is coming from a binding phenomenon which needs to be taken into account and corrected for or our wines risk not being protected in spite of us making sulfur additions.

I urge everyone to take a few minutes and read the entire article: http://morewinemaking.com/public/pdf/so2.pdf.

Thank you Mr. P and Mr. T. Extremely helpful.