to get firmer for some days or weeks.
Two kinds of pectin gels. Left: In ordinary
fruit preserves, the cook causes pectin
molecules to bond directly to each other and
form a continuous meshwork by carefully
adjusting acidity and sugar content. Right: A
modified form of pectin (low methoxy) can be
bonded into a continuous meshwork by means
of added calcium ions (the black dots), no
matter what the sugar content. This is how
low-sugar preserves are made.
The usual problem with preserve making is
failure of the mix to set even at the proper
boiling temperature and sugar concentration.
This can be caused by three different factors:
inadequate amounts of either acid or good-
quality pectin, or prolonged cooking that