How detailed to be when adding sulfites?

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Oct 25, 2016
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S. Jersey/Philadelphia area
The more research I do the more questions I have. I'm curious as to how detailed and specific you guys get when calculating how much sulfites to add.
I've been erring on the side of caution, and round down with my ballpark numbers to make sure I don't overdo it (until I get an so2 test kit that is).
Basically my question is how do you guys decide on sulfite amounts without free so2 testing? I know the pH level, and I know I need above average amount of free so2 since I am trying to save a batch that had bacteria growth.
And that's also the same ratio Ive always used. Its been "idiot proofed" and printed right on the bag for me. But then I did something that ruined my nice uncomplicated usual process: I googled.
I put myself in a position now that I'm trying to get the maximum amount of sulfites to work overtime since their work has been piling up on the desk while they were on vacation.
I have a vinmetrica meter and check pH and free SO2.

I contend that it is more important to know the pH than the free SO2, since the SO2 need varies widely depending on the pH. With kits and buckets, you can be pretty darn certain you pH is going to be right around 3.5. This is why the 1/4 tsp (1.5 grams) for 5 gallons (50 ppm free SO2) every three months for kits/buckets is a safe addition, for two reasons.
1. The wine will be microbial stable, because the efficacy of the SO2 is strong at this level, given this ideal pH condition.
2. Even if you err a little on the high side, your total additions over a year time is under a taste/smell detectable level.

However, if you are making wine from grapes, pH can vary greatly. This year my Chardonnay came in at 3.2, my Syrah 4.2. The acid in a 3.2 pH wine is 10X stronger than in the 4.2 pH.

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