English

Noun

reefer’s nut ‎(plural reefer's nuts)

1. The centre part of a ship’s biscuit. This part was compressed and even harder than the rest of the biscuit.

References

Acquired Tastes: Celebrating Australia's Culinary History, Colin Bannerman (and others), published by the National Library of Australia, 1998, ISBN 0-642-10693-2, page 10.