Definition of hot-iron test in US English:

hot-iron test

noun

Cheese-making
historical
  • A test to determine the acidity of cheese curd, in which a piece of dry curd is melted on a hot iron bar and then slowly removed, and the length the strands of melted curd reach before breaking is estimated, longer strands correlating to higher acidity.

Origin

Late 19th century; earliest use found in The Janesville Gazette.