Butter Question

[NorthernRaider]

A damn useful cooking ingredient made from freshly squeezed cows, However how can we store it LONG term without refrigeration, I think I saw on a TV show staring Ben Fogle about people living WAAAAY off grid, on one episode he was on a sailing boat in the south Pacific with a totally self reliant couple who had no fridge on her boat. So IIRC she preserves butter by melting it and pouring it into glass mason jars leaving a bit of a gap at the top, when it cools she pours salt water (brine) on top of the butter then puts the lid on, this apparently preserves the butter for months.

Can anyone please confirm this as I cannot find any other reference source?