“The cream rises until it sours”

Dr. Laurence J. Peter, along with co-author Raymond Hull (1919-1985), wrote The Peter Principle (1969), stating “in a hierarchy every employee tend to rise to his level of incompetence.” The authors also stated it another way:
 
“You will see that in every hierarchy the cream rises until it sours.”
 
“The cream rises until it sours” is the less-frequently used shorthand explanation of the Peter Principle.
 
     
Wikipedia: Laurence J. Peter
Dr. Laurence Johnston Peter (September 16, 1919 – January 12, 1990) was an educator and “hierarchiologist”, best known to the general public for the formulation of the Peter Principle.
 
OCLC WorldCat record
The Peter principle,
Author: Laurence J Peter; Raymond Hull
Publisher: New York, W. Morrow, 1969.
Edition/Format:   Book : English
Summary:
In dead pan humor, the author tells why the world is so screwed up, why humans fail, and how to achieve a state of well-being, avoiding the ultimate promotion.
 
31 March 1969, Seattle (WA) Times, pg. 53, col. 4:
The Peter Principle
Hierarchy: Cream Rises Until It Sours

(Second of a series)
By DR. LAURENCE J. PETER AND RAYMOND HULL
(>>>)
LOOK around where you work, and pick out the people who have reached their level of incompetence. You will see that in every hierarchy the cream rises until it sours.
 
13 April 1969, New York (NY) Times, Book Review, pg. 22:
The Peter Principle; By Laurence J. Peter and Raymond Hull. 179 pp. New York: William Morrow & Co. $4.95.
BY PAUL SHOWERS
(...)
As the authors observe, “the cream rises until it sours.” Messrs. Peter and Hull omit nothing.
   
New York (NY) Times
Laurence J. Peter Is Dead at 70; His ‘Principle’ Satirized Business
By JAMES BARRON
Published: January 15, 1990
(...)
Cream Turns Sour
Dr. Peter found such people in businesses, school systems, government agencies, churches and political parties. ‘‘The cream rises until it sours,’’ he wrote, summarizing the result: every bureaucracy was inevitably made up almost entirely of people inadequate to their tasks.
 
Google Books
If things are so good, why do I feel so bad?
By George Barna
Chicago, IL: Moody Press
1994
Pg. 210:
“The cream rises until it sours,” Peter wrote in 1969; a quarter-century later, America is drowning in a sea of soured cream.
 
The Economist
Guru
Laurence Peter

Jan 22nd 2009
Not many management gurus have their name adopted for a principle, especially when they are not really a guru at all. The Peter Principle is encapsulated in the phrase: “In a hierarchy, every employee tends to rise to his level of incompetence.” It first appeared on the cover of a book of the same name, written by Laurence J. Peter (1919-1990), a teacher and professor of education, and Raymond Hull, and it has since become part of the English language.
 
Written in a mock 19th-century style and illustrated with 19th-century engravings from Punch, a British humorous magazine, the book was an instant hit. Peter’s Corollary stated: “In time, every post tends to be occupied by an employee who is incompetent to carry out its duties” or “The cream rises until it sours.”