Is chewing a mouthful of food forty times a Sunnah?

Chewing food forty times before swallowing is not part of the Sunnah, even though chewing food is considered among the etiquettes of eating and helps preserve health. There is no authentic narration from the Prophet, peace and blessings be upon him, commanding to make bites small or to chew thoroughly before swallowing. It was narrated from Al-Shafi'i that vigorous chewing is among the Sunan (practices) of eating.