Plants store their carbohydrates in part in the form of sugar. Cane sugar, or sucrose (C12H22O11), was formerly obtained almost entirely from the sugar cane, but now the largest amount of sugar on the market comes from the sugar beet. Chemically, cane sugar and beet sugar have the same properties and cannot be distinguished. In the refining of sugar the juices of the cane or beet are extracted by crushing and pressure, and then go through a process of purification ; the resulting liquid is boiled down to a state of crystallization. As all the sugar will not crystallize, this liquid is drained off and constitutes molasses. When heated, cane sugar melts and forms barley sugar, and at a still higher temperature, caramel is formed; this latter has a brown color and distinctive flavor and is used for coloring and flavoring in cookery. Sugar loses part of its sweetness by this process.

Maple sugar (C12H22O11) is obtained by boiling down the sap of the maple tree.

Lactose or milk sugar (C12H22O11) is present in the milk of all mammals. It is the form of carbohydrate that is best for a young child until it is a year old. Lactose is obtained commercially from the whey left as a residue in cheese making. It is not as sweet as cane sugar. When milk is modified for infant feeding, lactose is the form of sugar which should be added.

Glucose or grape sugar (C6H1206) is widely distributed in nature and is found in fruits and plant juices, and in small amount in the blood of animals. It is not as sweet as cane sugar and does not crystallize as readily. It is usually sold in the form of a clear, heavy syrup.

Glucose is obtained commercially by treating starch with an acid, which causes the following change to take place:

C6H10O5 + H20 = C6H12O6 Cane sugar is inverted, or changed to glucose, when boiled with an acid. Acid fruits which are cooked for some time with sugar are, therefore, not as sweet as when the same amount of sugar is added after cooking. Glucose will ferment with the action of yeast, but cane sugar must first be changed to glucose by the enzyme of yeast before fermentation will take place.

Note

Show samples of cane sugar, beet sugar, milk sugar, glucose.

Experiment 29

Put 1/4 c. sugar in an omelet pan and stir over a moderate fire until it melts. Remove a portion of the syrup, which is barley sugar. Continue the heating until the mixture browns slightly. Pour all but a small amount of this on an un-greased tin to cool. This is caramel. Continue heating a small amount of the sugar until it burns or carbonizes.

Experiment 30

Pour sulphuric acid (H2S04) on a small amount of dry sugar. The acid will remove the water (H20). What other element is present in sugar ? Repeat experiment with glucose.

Fehling Solution

Five cubic centimeters of copper sulphate solution, 5 cubic centimeters of alkaline Rochelle salts, 20 cubic centimeters of water.

Boil all together for two minutes.