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If you chew an unsalted cracker and hold it in your mouth for two full minutes without swallowing, something weird happens: it starts to taste distinctly sweet.
Your saliva breaks down complex carbohydrates into simple sugars, but how can we actually prove which specific molecules are present in a clear liquid sample?

The Iodine Test for Starch

A polymer is a large molecule made of repeating chemical subunits called monomers, and starch is a plant energy-storage polymer made entirely of linked glucose units.
To detect starch, scientists use Lugol's iodine solution, which is potassium iodide mixed with elemental iodine dissolved in water.
Starch coils into a three-dimensional spiral, physically trapping linear polyiodide ions inside its core to absorb light and create an intense blue-black color change.
If starch is absent, the reagent does not react and simply keeps its natural yellow-brown tint.
So the cracker starts full of starch — but what specific sugar does your saliva turn it into?

Benedict's Test for Reducing Sugars

A reducing sugar is any sugar that possesses a free chemical group capable of donating electrons to another substance.
In 1908, American chemist Stanley Rossiter Benedict invented a bright blue copper solution to rapidly screen for glucose in human urine to detect diabetes.
Benedict's reagent contains blue soluble copper(II) ions (Cu2+Cu^{2+}), which gain electrons from reducing sugars when heated to form an insoluble red copper(I) oxide precipitate (Cu2OCu_2O).