It's not just spice that must flow: coffee, as detailed in Herbert's Dune novel.
'“The marker for Jamis’ coffee service,” Stilgar said, and he lifted a flat disc of green metal. “That it shall be given to Usul in suitable ceremony when we return to the sietch."'
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Coffee is a surpisingly important element in the Dune universe, at least in the first novel (which I just finished re-reading). It's mentioned several times both on and off Arrakis. In particular, the Fremen on Arrakis are drinking spice coffee, infused with the spice melange. Herbert doesn't go into detail about the preparation, but the drink is mentioned quite often in the novel. It was really the scene mentioned above that really caught my attention. As in many cultures, coffee is ore than a simulating drink, it's a part of life, and in particular, hospitality:
"The Reverend Mother said a ruler must learn to persuade and not to compel. She said he must lay the best coffee hearth to attract the finest men.”
After killing Jamis, Paul Muad-Dib Atreides inherits his coffee service along with his family, so clearly coffee is seen as an important component in Fremen life, which, given the clear association between the Fremen and the Arabic cultures, is no great surprise. Coffee came to us through the Arabs, after all.
"The marker for Jamis’ coffee service,” Stilgar said, and he lifted a flat disc of green metal. “That it shall be given to Usul in suitable ceremony when we return to the sietch."
Exactly how it's prepared is not mentioned, but my head canon says it's possibly something akin to the Ehtiopian coffee ceremony, or possibly served like Turkish coffee. Spiced coffee is frequently mentioned, so now I'm tending to prefer the latter, especially given the concern over water use among the Fremen. it would be prepared with as little water as possible, and advanced as the Fremen are technologically, i don't see them using espresso machines.
Finally, to illustrate the importance of coffee on Arrakis, the appendix mentions that the Planetary Ecologist Pardot Kynes and his son Liet-Kynes incorporate coffee trees into their vision of Arrakis' ecological future, a future shared with and taught to all Fremen.
Now came the crucial test: date palms, cotton, melons, coffee, medicinals—more than 200 selected food plant types to test and adapt.
The final stage of the building of a water-based ecology mentions coffee plantings among other species, and in my head canon, it's
Coffea arabica, of course. Clearly the drink and the plant are important to these people.¹
¹ https://dune.fandom.com/wiki/Coffee
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