There is no argument that the expression refers to casual, idle conversation, but there are several disputed sources of its origin. Wikipedia observes that there is no evidence that it came from the often sited reference of sailors chewing salt-hardened fat or Native Americans chewing animal hides in their spare time. Ditto for Inuit chewing whale blubber. The actual origin is attributed to soldiers in the British Army in India who chewed on the cloth soaked in animal fat that contained the powder and ball for loading their muskets. They chewed on the cartridges “…to pass the time and reduce nerves, and in some cases to stave off cravings for chewing tobacco.”   It was first referenced in 1885 in a book by J. Brunlees Patterson titled Life in the Ranks of the British Army in India.