Jefferson wrote that the milk used to make parmesan was "scummed" and then placed in a large copper kettle. After four hours in the kettle, he wrote, "the whey begins to separate" and a small portion of saffron is used to "give colour" to the cheese. Then it is heated "by a quick fire," wrote Jefferson, until the curd hardens and separates.
Jefferson used nearly 500 words to record just about every detail of parmesan making -- from the amount of salt that was added to the precise number of days it took the cheese to "ripen."
(Note: Jefferson's culinary observations during his travels to Europe during the 1780s are contained in this book, edited by Anthony Brandt.)