Thanks for the comments Steve.
I should mention to all that I sent out different pictures to each group. Both prints developed in Caffenol. One set 'The Lizzard' was 1 litre of caffenol used already to develop two rolls of 120 film, left in a bottle for a while and then used to make prints. The second was Caffenol mixed up to develop film, but never got around to it, and I think a month later developed the set of 'Fungus' prints.
To cut down the loooong development times in Caffenol I have the chemistry quite warm 25 to 28°C. This would be what brings out the grain in the paper I expect.