This is a common occurrence with several explanations, any or all of which may be happening:
- Make sure you are using fresh sulfite powder. Potassium metabisulfite degrades over time and that stuff you bought 2 years ago is probably bad now!
- Make sure that you stir your wine thoroughly when you add sulfite. If you pour a 10% solution of KMBS into your wine, it sinks like a battleship! A sample taken off the top will read low unless the wine is stirred.
- A significant portion of the sulfite you added may have ended up ‘bound’, particularly if your free SO2 was very low to begin with. This bound SO2 does not show up when you measure free SO2, and it is not protecting your wine. You will need to add more sulfite until your free SO2 comes up to the right level. Sometimes you must add 2 or even 3 times more sulfite than you first calculated.
Posted in: SO2 Questions