Using sulfite (SO2) to protect wine

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Using sulfite (SO2) to protect wine

Grape must and wines are protected from microbial action and oxidation by adequate levels of sulfur dioxide (SO2).  Typically you add the SO2 to wine via a solution containing 10% potassium metabisulfite.  The required amount of sulfite solution depends on the pH of your wine.  White wines require more sulfite protection than red wines for the same pH level.

Making your 10% Potassium metabisulfite solution

Potassium metabisulfite (a white powder) is widely available in 250 gram bags.  Buy a bag.  To make a 10% solution:

  1. Select a 500ml or 1L bottle (the 1L bottle is more convenient for people who make lots of wine).  Partially fill the bottle with clean water (distilled or filtered water is preferable).
  2. Measure out 50 grams (for the 500ml bottle) or 100 grams (for the 1L bottle) of metabisulfite and add carefully to the bottle through a funnel.  Be careful to breath as little of the metabisulfite dust as possible.
  3. Top the bottle with more water, shake, and wait until all the metabisulfite crystals are dissolved.

Your solution is now ready to use.  Newly created solutions have little smell.  Later on, as the SO2 is released, you will experience a very sharp sulfite  nose.  Don’t breath the fumes any more than you have to.  A solution will last about 6 months if tightly sealed.

Required SO2 levels and metabisulfite additions

For adequate protection, white wines require 0.8 ppm of molecular SO2 and red wines require 0.5 ppm.  The amount of molecular SO2 available from your metabisulfite solution depends on the pH of your wine.  You need to add more free SO2 the higher the pH.  Read the free SO2 level required from the left hand columns of the table below.  Then use the right hand columns to determine how much 10% solution to add to obtain a particular level of free SO2.

 

How much metabisulfite to add to your wine

pH Free SO2
required in ppm
Free SO2
required in ppm
ml of 10% metabisulfite solution required for
White Red 1L 19L 23L 55L
3.0 13 8 10 0.18 3.3 4.0 9.6
3.1 16 10 15 0.26 5.0 6.1 14.6
3.2 21 13 20 0.35 6.7 8.1 19.3
3.3 26 16 25 0.43 8.3 10.1 24.1
3.4 32 20 30 0.53 10.1 12.2 29.2
3.5 40 25 40 0.70 13.3 16.1 38.5
3.6 50 31 50 0.87 16.6 20.1 48.1
3.7 63 39 60 1.05 20.0 24.1 57.8
3.8 79 49 70 1.23 23.3 28.2 67.4
3.9 99 62 80 1.40 26.6 32.2 77.0
4.0 125 78 100 1.75 33.3 40.3 96.3

 

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