"Cheese is the adult form of milk, no longer liquid but solid or semi-solid” was written by André Simon in his book Cheeses of the World (1956). The line is more frquently credited, however, to New York City-born novelist Richard Condon (1915-1996), who wrote in A Talent for Loving (1961): “Cheese. The adult form of milk.”


Wikipedia: André Simon (wine)
André Simon (28 February 1877 – 5 September 1970) was a French-born wine merchant, gourmet, and prolific writer about wine. Hugh Johnson describes him as “the charismatic leader of the English wine trade for almost all of the first half of the 20th century, and the grand old man of literate connoisseurship for a further 20 years”.

OCLC WorldCat record
Cheeses of the world.
Author: André Louis Simon
Publisher: London, Faber and Faber [1956]
Edition/Format:  Book : English

Google Books
August 1956, The Milk Industry, pg. 61:
A quotation from his introduction may perhaps illustrate this: “Cheese,” he (André Simon—ed.) writes, “is the adult form of milk, no longer liquid but solid or semi-solid.”

Google Books
Wine and Food
Issues 101-104
1959
Pg. 155:
I wish the scientists had bethought them that the adult form of milk is cheese.

Google Books
A Talent for Loving ; or, The Great Cowboy Race, a novel
By Richard Condon
New York, NY: McGraw-Hill
1961
Pg. 20:
“Until I was twenty-two years of age,” Heller answered, “I was sure my life would have been dedicated to cheese.”

“Cheese?”

“Yes. Cheese. The adult form of milk. Hard and soft; new, mature, and overripe. Graced with a spectrum of smells from wispiness to shocking assault on the nostrils; mild and bitter, salt or sweet, piquant or mellow.”

Google Books
Fabulous Fallacies:
More than 300 popular beliefs that are not true
By Tad Tuleja
New York, NY: Galahad Bks.
1982
Pg. 170:
The Swiss have been master cheesemakers for more than two thousand years—longer than any other people—and through much of their history, the manufacture and export of what Andre Simon calls “the adult form of milk” have been mainstays of the economy.

Google Books
Wisconsin Cheese:
A Cookbook and Guide to the Cheeses of Wisconsin
By Martin Hintz and Pam Percy
Guilford, CT: The Globe Pequot Press
2008
Pg. 107:
“Cheese: the adult form of milk.”
-- Richard Condon (1915-1996), American satirical novelist, playwright, and crime writer, from A Talent for Living (sic), 1961

The Ken-Speckle Letter Press
THE ADULT FORM OF MILK
Never let it be said that we don’t do anything cheesey. Misspelled French and all, here’s a print we originally did for the Northern Waters Smokehaus, our downstairs neighbors. One of the reasons we always smell fishy.