Pickles and preserves are refused because a fruit kept in brine or oil with its moisture in it ferments, and in fermenting breeds beings without number.
Sandhāna in the commentary is the preserve of bael and other fruits. The modern practice names the same thing more exactly: an athāṇu is fine while it is dry and refused once moisture has stood in it beyond a day, when it is boḷ, gone soft. It is the same reason as wine and as food that has turned: fermentation is life you did not ask for.
The twenty-two, laid by their reasons - Pickles highlighted