Sweetness is a quality that is detected by taste, but there is no exact test for it. Much depends upon how the test is conducted, whether the tongue is dry or moist, upon what part of the tongue the sample is placed, and with several other conditions, the fatigue of the sense of taste. Some persons detect sweetness in less concentrations than others. It cannot be expected that all people will agree in their estimates of the relative sweetness of the sugars, even with carefully worked out tests.

In rating the sweetness of the various sugars it is a commonly accepted practise to rate sucrose as 100. Sugars sweeter than sucrose are ranked higher than 100, and those less sweet are ranked lower.

Biester and Wood of the University of Minnesota give the following rating to sugars:

Levulose....................

173.3

Sucrose.....................

100.0

Dextrose....................

74.3

Maltose.....................

32.5

Lactose.....................

16.0

Sale and Skinner of the Bureau of Chemistry (Water and Beverage Laboratory) rate the sugars as follows:

Sucrose.....................

100

Dextrose....................

50

Levulose....................

150

Maltose.....................

50

Invert sugar.................

85

Paul in comparing the sweetness of several sugars with sucrose gives the following value:

Sucrose.....................

100

Dextrose....................

52

Levulose....................

103

Lactose.....................

28

A commonly accepted value of dextrose at the present time is about 70 to 75. There is the probability that this is too high and that 50 is a better figure. Levulose is conceded by all to be sweeter than sucrose, but again there is no agreement as to how much sweeter. Some authorities rank it 120 to 125. With the higher figures for the sweetening powers of dextrose and levulose it would seem that invert sugar should be sweeter than the original sucrose. But the manufacturers of carbonated beverages, to whom this would be beneficial, since they use solutions of sirup, do not think that invert sugar is any sweeter than sucrose, even though 342 units of sucrose yield 360 units of invert sugar or a gain of 5 per cent in weight.