system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the "sharp" in sharp cheddar? How are there various levels of "sharp"?
gpt
The term "sharp" tells you how long the cheese was aged.  Mild is 3 months, sharp is 9 months and extra sharp is more than 18 months.  As it ages, its texture also goes from smooth and creamy to crumbly by developing hard, salt-like crystals called calcium lactate.