Yam stood for manliness,
Since it was so hard to cultivate, yes. Also it was used in almost all dishes, thus there is so much yam in the book. As my teacher said, old yams were better. New yams, in the new year we're too hard and not that flavorful. But like the new year tradition to clean things out for the new year, the old leftover yams are thrown out. They don't mold, instead they develop a hard shell on the exterior
