The science and magic of jam-making

Commercial jams are the sickly sweet sisters of homemade jam, but a grasp of the science will help you get yours just right
Getting the pectin content of your jam right makes the difference between a semi-rigid, elastic 'gel' and sloppy fruit sauce. Photograph: R White/Corbis

The rule is, jam tomorrow and jam yesterday – but never jam today. Lewis Carroll

Jam-making conjures up images of domestic idylls, an escape to the mountains to live on your wits, and jam. The seemingly simple mixture of fruit and sugar held together by a web of pectin strands can be both beautiful and maddening. A jam worthy of a Woman's Institute rosette, however, might have a nature so tender that it quivers when cut with a spoon to reveal sparkling, ruby-like faces.

This sweet treat was named late, in the early 1700s, but "jam" captures the difference between it and the (in my opinion) inferior jelly. Jellies are made from homogeneous fruit juice with none of the wonderful texture-giving "crushed" fruit.

Jam as we know it only seems to have emerged in the 19th century. It took a cheap and reliable source of sugar from the West Indies to make jams affordable. Before this, sugar was considered a spice and the price in Europe was such that only the richest could afford it. Preserves made from sugar were too precious to spread thickly on toast. Instead they were eaten as "spoon sweets" with feasts being capped off with the distribution of delicate silver spoons laden with fruit preserves. You may still be offered such treats with a glass of cooling water in the Middle East and eastern Europe.