Panera Bread founder Ken Rosenthal passed away on Friday at the age of 81. He was surrounded by family and leaves behind his wife, Linda "Laya" Rosenthal, and their four children.

Pallant’s “Sourdough Culture: A History of Bread Making From Ancient to Modern Bakers,” details his quest to find the origins of his sourdough starter. The book comes out on September 14.

Panera Bread founder Ken Rosenthal passed away on Friday at the age of 81. He was surrounded by family and leaves behind his wife, Linda “Laya” Rosenthal, and their four children.

Kenneth “Ken” Rosenthal, who founded the company that later became Panera Bread, died on Friday, Feb. 14. He was 81.

Ron Shaich co-founded Panera Bread and ultimately sold the company for $7.5 billion. He credits his success to starting at the end and planning backwards.