well-boiled congee or gruel, thick, rich
飦 centers on a thick, well-boiled rice porridge or gruel, emphasizing its rich, concentrated consistency.
飦 combines the food radical 飠 with 干, which likely contributes a phonetic element. The exact historical development is uncertain.
The food radical 飠 suggests something edible, and 干 looks like a drying rack. Imagine rice porridge boiled until it is so thick and rich that it could almost be hung out to dry.
For ケン, picture a thick, rich congee served in a can: can -> ケン, and the can is filled with the well-boiled gruel.