Jams appeared in Europe rather late. Indeed their making requires sugar, almost unknown in Europe until the the Crusades.
The Roman cooking already knows candied fruits with honey, and since the expeditions of Alexander the Great, Europe have heard of the "reed which gives honey without bees's help". But this half mythical substance and his more wide-spread substitute, honey, are far too expensive to be a convenience good.
In addition, if the sweetened taste already exists at the time, it does not take the same shapes as today. The aristocratic meals composed with meat of bitter-sweet taste makes the desserts and separated sugar refineries less necessary. As for the lower classes, they eats neither sugar refineries, nor fruits. The vegetables, which grows in the ground, are regarded as an appropriate food to their social status. The fruits on the contrary, which grows out of the ground, and even more the trees fruits, are reserved for symbolic reasons to the nobility.
It is the contact with the Arab world which makes Europe discover sugar, and with it jams, or rather “letuaires”, as one says at the time. However it is not as a softness that jams get their place, but as a medicine. Indeed, the word letuaire, from Latin “eleucterium”, means “medicine to lick”. And during all Middle Ages one primarily makes jams for this use. It is as a doctor that the famous Nostradamus writes a treaty on jams, and it is for health reasons that Gargantua of Rabelais always finishes his meals with quince paste.
Little by little, the benefits given to sugar are combined with simple greediness. Confituriers and Confectioners enter the service of great houses, then sells their productions in shops. It is the case of the famous parisian confectioner Roger de Quiquetonne who gave his name to Tiquetonne street in Paris.
The first warnings against sugar at the beginning of the 17th century had little impact on the success of jams productions. At that time, the word jam means indifferently fruits with syrup, candied fruits, candies, and fruits cooked with sugar. It is only at the 19th century that one limits it to the last case of figure.
The rise of jams is also related to the replacement of cane sugar by beet sugar, cultivated on the spot thus definitely cheaper. It is only as from this moment that sugar becomes a convenience good, allowing the development of an industry of jams, and the generalization of home making.
(source : Confitures Merveilleuses)
We perpetuate this tradition today by preparing our jams in the manner of our defer grandmothers. Cooking in copper basin ensures a perfect consistency of the jams. The slightly widened shape of the basins facilitates also the evaporation of the water contained in the fruits, and it is only the sugar which makes the jams preserved. It is also possible to add an acidifier (lemon juice) to prevent formation of sugar crystals.