This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
Review a study of starch, p. 68.
A. Examine granulated white sugar, and (if possible to obtain it) some solid glucose. In which are the particles most distinct? Taste each. Which is the sweeter? If solid glucose is not obtainable, use commercial glucose, " corn-syrup."
C. Heat a little sugar slowly in a test-tube till it melts. What forms on the sides of the tube? What two elements must sugar contain? Pour out some of the liquid. Continue to heat the rest till it turns brown. Heat the rest till only a dry black substance is left. What do you think this is?
D. Repeat these experiments with glucose.
E. Put into a test-tube a little of the glucose solution in the glass. Add a few drops of Fehling's solution and boil. What happens? Try the same experiment with the sugar solution. If you had a can of syrup and you did not know whether it contained glucose, how could you find out?
In what ways are sugar and glucose alike? How do they differ? In what ways do both resemble starch? (See experiments in heating starch, p. 69.)
Like starches, they are composed of carbon and of hydrogen and oxygen in the right proportion to form water. Starches can be changed into sugars. (See p. 70.)
When we use the word sugar, we usually mean the kind of sugar in most common use, that which is made from sugar-cane or from sugar-beets. But there are many sugars, just as there are many starches. Cane-sugar and beet-sugar, however, are not really two different sugars. They are chemically the same, and the name cane-sugar is applied to both. Glucose is also a sugar, but it has different properties from cane-sugar. It is less sweet and less soluble than cane-sugar, and it does not readily form crystals as cane-sugar does. With Fehling's solution glucose forms a red precipitate. Cane-sugar does not. Cane-sugar melts at 320°, forming a clear liquid. When cool this remains transparent and is called barley sugar. At a higher temperature the liquid becomes brown. Some of the water has been driven off, and a mixture of dark-colored substances called caramel is formed. Caramel is used for coloring and flavoring. When all the moisture is driven off, only carbon is left.
Glucose is known also as grape-sugar because it is abundant in grapes. When grapes are dried to make raisins, the grape-sugar appears on the surface in grains, as it does also on other dried fruits. It occurs in many fruits and some vegetables, usually with another sugar, called fruit-sugar, or fructose.
When cane-sugar is boiled with acid, some of it splits into grape-sugar and fruit-sugar.
Milk-sugar is prepared from milk for use in infant's food and in medicine. Honey consists chiefly of glucose and fructose with flavoring matter from the flowers. It was used for sweetening before cane-sugar was known.
The chief sources of cane-sugar are the sugar-cane, sugar-beets, the sugar-maple, the sugar-palm, and sorghum. Americans and Europeans use mostly cane- and beet-sugar. Sugar-cane is a tropical grass, higher than corn. Sugar-beets are large and white. They grow in different climates, including places where it is too cold for sugar-cane.
In cane-sugar factories the juice is squeezed out of the canes between rollers. In beet-sugar factories, the beets are sliced into strips and the juice dissolved out of them in tanks of warm water. After this the process is similar in all factories. The juice is purified, filtered, and boiled down 1 to a syrup. This syrup is boiled again till sugar crystals form. The sugar is separated from the uncrystallizable part of the syrup in a centrifugal drier, a wire basket which throws the syrup out as it revolves. This "raw sugar" varies in grade and color. Some of it, including brown sugars, is sold without refining. Most of it, including all beet-sugar, is refined. Granulated sugar has been refined, dried, and sifted. Cube or domino sugar has been refined, and either moulded and sawed or pressed into blocks. Pulverized and confectioner's sugar are made by grinding and sifting the fragments of block sugar. Brown sugars are less refined grades. Refined white sugar is said to be the purest manufactured food we have.
1 All boiling is done in vacuum kettles and pans. These are air-tight vessels from which part of the air has been drawn out to lower the boiling-point and so avoid burning the syrup.
It is rarely adulterated. But it is blued, much as clothes are. Manufacturers declare it would not sell if left its natural creamy color. What do you think about this?
The uncrystallizable syrup separated from sugar forms molasses. "Porto Rico" molasses is darker than "New Orleans." Modern methods of sugar-making do not produce the rich dark molasses of former days.
Test molasses with litmus paper. Is it acid or alkaline? If acid, put a little in a test-tube and add a pinch of baking-soda. Test again. What does the foaming of the molasses show? (P. 108.)
Old-fashioned molasses was distinctly acid, and soda could be used with it to make batters light. If molasses is only slightly acid, or if only a little molasses is called for by the recipe, some baking-powder must be used besides the soda. Canned molasses may not be acid at all.
Table syrup is also made from cane-juice.
Weak acid acts on starch as diastase (amylase) does, converting it into a mixture of sugars and gums, finally into glucose. In this way great quantities of syrup are made from starch and sold as "glucose" or "corn-syrup." The process is stopped when the liquor is about half dextrose and half dextrin. It contains a small quantity of mineral matter, which gets in during manufacture. Neutralized and purified, it forms a clear syrup. As it is almost tasteless, it is usually flavored with cane-sugar. This "commercial glucose" is said to be essential to the making of some kinds of candy. As it is much cheaper than cane-sugar, manufacturers who use it in canned fruits are required by law to so state on the label. Solid glucose (commercial dextrose) is used for manufacturing purposes only. It comes in angular pieces, light-brown in color and brittle.
Sugar is digested in the small intestine, where it is split into glucose and fructose. In small quantities it is completely digestible, and is rapidly absorbed. When eaten in excess, some of it is likely to undergo acid fermentation instead of digestion.
Sugar is equal to starch as a source of muscular energy. Ordinarily we could not substitute sugar wholly for starch, because sugar is too rapidly digested to be handled by the body as advantageously as starch is. But in cases where great energy must be exerted in a short time, increasing the amount of sugar in the diet gives working power and delays fatigue. It has been noticed that lumbermen and hard-working farmers consume quantities of cakes, preserves, and other sweet stuff. Athletes and soldiers on the march tire less quickly when allowed extra sugar. It is natural that children, who are so active, should crave sugar, and right for them to have a certain amount of it. One virtue of sugar is its flavor, which makes other foodstuffs more palatable. There is danger, however, of its being used to excess just because it tastes good. It is a mistake to use so much sugar, either in cooking or at the table, that the mildly pleasant flavors of other foods are lost. Lunching on sweets and habitually eating candy between meals overburdens the system. Home-made candy is safest, especially for children.
U. S. Department of Agriculture Office of Experiment Stations A. C. True: Director
C. F. Langworthy
Expert in Charge of Nutrition Investigation;
Composition Of Food Materials.