This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Strong alkalies, like strong acids, decompose the sugars. Weak alkalies or salts with alkaline reaction, like sodium bicarbonate, common baking soda, also act upon the sugars. Even alkaline salts found in hard water may produce considerable decomposition in some of the sugars. Of the disaccharids those most easily affected by acids are least readily decomposed by alkali, and vice versa. Sucrose is scarcely acted upon by a weak alkali, but maltose and lactose are affected more readily.
The monosaccharids are easily decomposed by alkalies, even very weak ones. If the sugar is allowed to stand in a solution with a weak alkali many substances may be formed. Decomposition is brought about so rapidly with strong alkalies that not so many products are formed with it. Nef states that, of the 116 possible decomposition products with dextrose and a weak alkali, 93 have been isolated. Very weak alkalies may cause rearrangement of the molecule. In the manufacture of dextrose great care must be taken to keep the reaction acid to prevent an off color and taste. The action of an alkali upon dextrose produces first a yellow tinge which becomes deeper and finally brown if carried far enough. This decomposition is called caramelization. With very slight caramelization of dextrose the flavor may not be very noticeable, but it may become strong and bitter, and characterized by a strong, pungent, acrid after-taste. In sections of the country where the water is very hard, enough decomposition to affect the flavor may be brought about in ordinary cooking. This is more noticeable when the sugar is cooked slowly. The addition of a little lemon juice, vinegar, or the acid salt, cream of tartar, will prevent the discoloration and the change in flavor. In some instances this browning or caramelization is an advantage. For example, baked beans brown better when dextrose is added than when sucrose is used.
Levulose, like dextrose, is unstable in an alkaline solution, decomposing as readily or more so than dextrose and giving many decomposition products. But in cookery its decomposition by alkalies can be prevented in the same way as that of dextrose. Candy made from honey often has a strong flavor that may be rather disagreeable, owing to decomposition of the dextrose and levulose during cooking. If just enough acid is added to combine with the alkali present, the characteristic flavor of honey is retained.
Moisture-Absorbing Power of the Sugars
All sugars should be stored in a dry place for they deteriorate if stored where it is damp. This power of absorbing moisture can be made use of to improve some foods, but it is a detriment in others.
Browne reports that the sugars having the highest absorptive power from a saturated atmosphere are the levulose-containing substances: invert sugar, honey, levulose, and molasses. He finds that the percentage of water absorbed has no relation to the percentage of levulose present. This would suggest that cakes made with levulose-containing products would not dry out so rapidly as cakes made with sucrose. In practise, this is found to be true. Cakes made with part levulose or levulose-containing substances do not dry out so rapidly as those made with sucrose.
Honey and molasses are used in many family recipes for cookies, particularly the kinds made for holidays, for they can be made a long time in advance of their intended use and they remain moist with storage - in many instances the moisture content seems to increase during storage.
Invert sugar either added to food or formed by inversion during cooking is found in many food products. In the bakery trade it is used to prevent drying and checking. The acid in fruits inverts sucrose. The amount of total sugar that can be held in solution in a given quantity of liquid is greater if it contains a mixture of sucrose, levulose, and dextrose. Rich preserves made of fruit containing little acid do not crystallize so readily during storage if lemon juice is added when they are being made. The lemon juice brings about more inversion than the less acid fruit juice. The invert sugar does not crystallize so readily as the sucrose, the total quantity of sugar held in solution is greater, and there is less evaporation.
The levulose-containing substances should be avoided for hard candies. Duryea states that maltose is better to use in hard candies than dextrose, because the candies remain drier. He also adds that another advantage of using maltose in hard candy is that maltose is not so readily affected by alkali. The decomposition caused by use of dextrose and alkaline water is avoided.