Sugar Preserves

Another venerable technique for preserving fruits is to boost their sugar content. Like salt, sugar makes the fruit inhospitable to microbes: it dissolves, binds up water molecules, and draws moisture out of living cells, thus crippling them. Sugar molecules are quite heavy compared to the sodium and chloride ions in salt, so it takes a larger mass of sugar to do the same job of preserving. The usual proportion by weight of added sugar to fruit is about 55 to 45, with sugar accounting for nearly two-thirds of the final cooked mixture. Of course sugar preserves are very sweet, and this is a large part of their appeal. But they also develop an intriguing consistency otherwise found only in meat jellies—a firm yet moist solidity that can range from stiff and chewy to quiveringly tender. And they can delight the eye with a crystalline clarity: in the 16th century, Nostradamus described a quince jelly whose color “is so diaphanous that it resembles an oriental ruby.” These remarkable qualities arise from the nature of pectin, one of the components of the plant cell wall, and its fortuitous interaction with the fruit’s acids and the cook’s added sugar.