Cane sugar is probably the most important member of the sugar groups. It is obtained from the sugar cane and the sugar beet, the two forms being identical chemically. It can be obtained in a high state of purity, often up to ninety-nine and eight tenths per cent. The English-speaking races use the largest amount of this sugar, in some countries averaging as high as eighty-five pounds per capita a year. Cane sugar is white, crystalline, soluble in water, and has a very sweet taste.
Malt sugar is obtained from grains, such as barley or wheat, by allowing them to sprout. During the sprouting process, there is developed in the grain a ferment that is capable of changing starch to malt sugar. After the malt diastase, as the ferment is called, has had a chance to convert the starch to malt sugar, the sugar is extracted with water, and the resulting solution evaporated to a sirup. This sirup can be evaporated further and the malt sugar or maltose taken out as a solid; but it is usually used in the form of a sirup. This maltose is a natural product to the body, as it is formed by the saliva and the pancreatic juice when they act upon starch.
Milk sugar is found to the extent of about five per cent in cow's milk. It is obtained as a by-product in the manufacture of cheese. The whey, or watery fluid left after the removal of the curd, is evaporated and purified until a fine, white, rather gritty powder, or in some cases a crystalline solid, is obtained. This milk sugar, or lactose, is soluble in water, and has a fairly sweet taste. Lactose is one of the essential food elements for the normal growth of a child or a young animal. Hence one can see why children cannot be reared easily without milk.
Glucose is the most important sugar in the third group of carbohydrates as given above. It is found naturally in many fruits, and is here called grape sugar. It is the normal sugar of human blood, and in this connection, is usually called dextrose. Glucose is made commercially by boiling starch, most frequently cornstarch, in water, to which sulphuric acid has been added up to one to one and one half per cent. After sufficient boiling, the acid is neutralized with lime, and the sugar separated by chemical methods. If the process is carried out carefully, and reasonably pure reagents are used in the process, the result will be a sirup of fair purity and one of value as a food. Impure and poorly made samples of glucose have given this otherwise wholesome sugar a bad name.
Glucose can also be obtained in solid form by continuing the process of purification a few steps beyond the sirup stage. But let it not be forgotten that any of the sugars, taken in large amounts, may overload the digestive system and the liver, and hence they should be used in reasonable amounts.
Levulose, called also fruit sugar, is found in some of the sweet fruits and in bees' honey. The chief sugar of honey is called invert sugar, and is really made up of equal parts of dextrose and levulose. It is present up to seventy-five per cent in good samples of honey. These sugars, properly used, are excellent foods.
Importance of Carbohydrates
The carbohydrates are our chief source of heat and energy, and as previously stated, furnish sixty to sixty-five per cent of the total fuel value of our food. Each ounce of pure carbohydrate yields one hundred sixteen calories of heat when burned. In caloric yield, they are equal to the proteins gram for gram, but yield less than one half that of the fats. If two thousand five hundred calories are again taken as our standard, then sixty per cent would make one thousand five hundred calories to be furnished by the carbohydrates. At one hundred sixteen calories an ounce, we find that it would require thirteen ounces of pure carbohydrate a day to balance this part of our diet.