Here's why:
* Concrete nouns refer to things that can be perceived by the senses (sight, touch, smell, taste, hearing). Sugar is a substance you can see, touch, and taste.
* Abstract nouns refer to ideas, concepts, qualities, or states of being that cannot be perceived by the senses. Examples include love, happiness, justice, and freedom.
While the concept of sweetness associated with sugar might be considered abstract, the sugar itself is a physical substance.