"Gritty" Foods-Why?

When you bite into a nice, ripe pear, your teeth will concounter a gritty feeling-what causes this? Are there little particles of sand/dirt in a pear?
Same with fine parmesan cheese-it has a gritty feel to it-what are these particles?

In pears they’re known as brachyscleridshttp://en.wikipedia.org/wiki/Ground_tissue#Sclereids and in Parmesan they’re calcium lactate. Similar calcium lactate cells will be found in old Gouda-- it has to do with amino acids breaking down during aging.

Thanx for the question and reply. I have wondered about pears possibly being sinister because of that characteristic.

Why does tapioca do what it does? A similar mechanism?