Book 27, Question 70
Why does old hard candy turn cloudy and sticky?
Fresh hard candy is sugar glass: the sugar was melted and cooled so fast that it never formed crystals.
Sugar likes water, so in humid air the candy’s surface soaks up moisture and turns sticky. Then the sugar molecules can move around and begin lining up into tiny crystals, which make the candy look cloudy and grainy. A tightly wrapped candy stays clear and glassy for much longer.