concentrate the other ingredients The boiling is continued until the temperature of the mix reaches 217–221ºF/103–105ºC (at sea level; 2ºF/1ºC lower for every 500 ft/165 m elevation), which indicates that the sugar concentration has reached 65% (for the relationship between sugar content and boiling point, see p 680) A fresher flavor results when this cooking is done at a gentle simmer in a wide pot with a large surface area for evaporation (Industrial manufacturers cook the water out under a vacuum at much lower temperatures, 100–140ºF/38–60ºC, to maintain as much fresh flavor and color as possible.) Now supplemental acid is added (late in the process, to avoid breaking down the pectin chains), and the readiness of the mix is tested by placing a drop on a cold spoon or saucer to see whether it gels Finally, the mix is poured into sterilized jars The mix sets as it cools below about 180ºF/80ºC, but firms most rapidly at 86ºF/30ºC and continues 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 goodquality pectin, or prolonged cooking that ... 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... 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... 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 goodquality pectin, or prolonged cooking that