This bread is only recorded in one source (Tales from The Xandrian Quarters) and even here it is attributed incorrectly by the narrator to human rather than dwarfish origin. Below is an extract.
It was burned pretty black on the outside and was curiously black within. Either it was a trick of the light or it actually looked to have a slightly green mottling. He waved this at me and then took a large crunchy bite.
"Peg brod!" he grinned."Yah wes! E's a good stuffa for 'ah trostrupp [sea-sickness]!"
As he spoke, bits of mashed up bread and stuff (let's leave it at that) shot from his mouth in a good impersonation of my own performance on the gunwale of the boat earlier. I had no idea what pig bread was at the time and I didn't have the stomach to ask. Actually, when I finally got around to it I rather wished that I hadn't. Apparently it was a bread that was made using pig fat and large quantities of salt (larger than for normal bread that is and added only after the dough had proved, to be precise). It was baked hard so that it was slow to decompose and was ideal for sea voyages.
I never found out what the green mottling was.
Source: The Xandrian Quarters