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Free SO2 as a function of pH and molecular SO2

by Charles Plant

The pH measurement of your wine affects your SO2 requirements.

Here is a table you can use to determine how much Free SO2 is required to adequately protect your wine from oxydation and bacterial infection, based on its pH reading. Effective protection is provided at about 0.8 mg/L molecular SO2. Maximum protection is achieved at around 2.0 mg/L molecular SO2. This is also close to the level at which SO2 can be detected by the senses.

Note: Milligrams Per Litre and Parts Per Million are effectively the same thing.

How to use this table

  1. Measure the pH of your wine.
  2. Look up your pH reading in the leftmost column of this table.
  3. Read across the table to determine the minimum and maximum values of Free SO2 you should consider using in your wine.
  4. Go to our SO2 Additions web page to see how to generate the required SO2.
Free SO2
pH readingMinimum effective protection
(0.8 mg/L molecular SO2)		Maximum protection before sensing
(2 mg/L molecular SO2)
2.8 9 23
2.9 12 29
3.0 14 36
3.1 18 45
3.2 22 56
3.3 28 70
3.4 35 87
3.5 44 109
3.6 55 137
3.7 69 172
3.8 87 216
3.9 109 272
4.0 137 342
4.1 172 430
4.2 216 540