There is
a vast trove of literature on sensory testing regarding sugar and other
sweeteners, as well as testing relative sweetness. For example,
the concentration of a sugar in solution can affect the perception
of sweetness - this is particularly true for the invert sugars,
glucose and fructose, and for the sugar alcohol, xylitol.
Temperature
is also a factor in sweetness perception.
Color has a strong
effect on perceived sweetness - red makes people think something is
sweeter than any other color; and green and yellow (associated with lemon and
lime flavors) gives the perception of less sweetness, even when the
colored solutions are all the same concentration. For this reason,
sensory testing is often done in rooms with red or green light, which
masks color differences in the foods being tested.
Brown
sugar is an interesting case. Although brown sugar has a lower amount
of
sucrose than refined sugar (92-96% depending on the manufacturer,
vs. 99+%), it can be perceived as sweeter than refined sugar. This is
because of the presence of ash components, invert, and sugar
degradation/browning products that enhance sweet perception. Brown
sugar is a complex mixture of ash, invert, small molecules with a sweet
/
caramel / brown sugar taste, acetic acid, and coloring polymers.
High
molecular weight coloring polymers (Maillard products and browning polymers)
are perceived as bitter, so with brown sugar, you have several tastes in
the mix. Since each manufacturer has his own way of making
brown
sugar, one can only make very general statements about it.