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 When sugar was used and it was said why whether foods could be saved, it learned by preservation with salt, but the cause over which foods rot or it mourns is putrefactive bacteria, and it is because moisture of the body of putrefactive bacteria will be taken and it becomes impossible to make a living, when there is 60~65% of concentration of the sugar in food.It is a problem of osmotic pressure.Predecessors use sugar for preserved food not getting to know about osmotic pressure.Jam evaporates excess water rapidly, and since it makes concentration high, fruit can save it for a long period of time.
 Sugar has in others the action which makes the sweet taste of the foods increase only by it being good for health or sprinkling on food.It developed as a method of eating fruit temporarily especially extractable in large quantities by jam processing with good appetite, or saving it.Sugar suitable for jam processing is granulated sugar, and can take out the frank sweet taste carried out frankly.
■Hydrophile property and a water holding property.
 Hydrophile property means that it is easy to melt into water, and sugar is the character to be easy to melt into water.That is because the molecule of sugar has a portion easily connected with the molecule of water.Sugar holds moisture, and the molecule of water is restricted and it becomes impossible to move it freely.

■Oxidization is prevented.
 By sugar being connected with moisture and absorbed water being made, oxygen becomes difficult to melt and it is connected with antioxidation.

■Sugar is good for recovery from fatigue!
 The grape sugar contained in sugar serves as cerebral energy.A brain will consume about 120g of grape sugar on the first.The lost grape sugar is suppliable with sugar.

■White sugar is an anti-diarrheal.
 There is work which works on white sugar at the stomach and intestines, and makes a pain ease.
 It is the Nara period that sugar got across to Japan for the first time, and it is said for Ganjin to have carried in.Since sugar of those days was valuables obtained only by import, it has been treated as medical supplies.Therefore, the method of preservation using sugar did not progress.
 The preservation which used sugar centering on Europe was already developed.
After the production technology of the sugar of India spread on the Mediterranean coast by conquest, it came to be known by the knights of the crusade, concentrating on Venezia and covering of countries it over the 11 to 13th century.However, since sugar was used as a precious medicine, it was only upper class persons who were able to be used for preservation of cooking and food, such as princes and an aristocrat.Cheap sugar can be soon got now from an overseas colony, the jam suitable for the climate of the area is made now, and it has long history.