fructose

Fructose is the sweetest of the common sugars, so frozen strawberry and banana alone can carry a smoothie with barely any sugar added on top. In this library it is the fruit's own sugar in a kiwi smoothie and a strawberry banana blend, and it is also the sugar hidden by design: in the Japanese curry, grated apple and a spoon of honey both dissolve into the sauce and leave their fructose behind, a sweetness meant to be felt rather than identified.

Fructose shares its formula, C₆H₁₂O₆, with glucose, but heat treats the two very differently: fructose is the first of the common sugars to caramelise, breaking down at around 105 degrees against roughly 150 for glucose, 160 to 170 for sucrose and 180 for maltose, a 75-degree spread hiding inside the single word caramelisation. It also forms where it was not before: boil fruit in sugar with an acid present, from lemon or from the fruit itself, and some of the sucrose splits into glucose and fructose, giving an inverted syrup that is sweeter than sucrose and resists crystallising.

The gut absorbs fructose more slowly once it outpaces the glucose alongside it, which is the mechanism behind the FODMAP tables: honey and high-fructose syrups rate high for exactly this excess, while a hundred grams of kiwifruit carries about 9 grams of sugar balanced closely enough against its own glucose to rate low, needing no added lemon and, most days, no sweetener. In this library fructose is traced in three recipes, always as the sugar a fruit or a spoon of honey brings rather than one added from a bag.