How does sugar act as a preservative in jam making?
Here is a good summary of the use of sugar as a preservative. All organisms require a narrow range of conditions in which to live: too acid or too sweet and nothing, not even bacteria can live (it might seem surprising that sugar is a preservative, but jam, so long as water doesn’t settle out is far too sweet for bacteria, plaques of mould on jam occur where water has formed on the surface, significantly diluting the concentration of sugar).
