One of the things I was told back when I had just started to dabble in medieval cooking was that the eggs they had in medieval Europe were smaller than modern eggs. Not being overly skeptical back then, I accepted this as an established fact and filed it away for future reference. As I progressed in my research though, I became more doubtful of this factoid. Now I'm at the point where I'm comfortable in saying it's utter bunk.
The recipe for May Eggs involves pouring the liquid yolks out of partly boiled eggs,
mixing them with spices, pouring them back in, and allowing them to boil until hard.
This is difficult and messy enough using large eggs. I doubt it's even possible with small ones.
It's easy enough to understand how such a belief could come about. We're told repeatedly that the great size of farm animals compared to their wild counterparts is directly the result of modern farming practices. What we forget is that some of those practices have been practiced for the past thousand years.
Evidence for modern-sized eggs in the medieval period is surprisingly easy to find.
The painting above is a beautiful example (click on it to go to a bigger version). See there in the lower right corner? Four Grade-A, Extra-Large eggs.
In this one the egg is on the floor, next to the overturned bowl and near the wooden shoe - about to be stepped on.
"Ah! How do you know those are chicken eggs and not goose eggs? How do you know they weren't smaller in, say, the 14th century?" I hear you ask. How about this for an answer?
Large, modern-looking eggs ... being gathered from chickens ... in the fourteenth century. That pretty much sums it up.
Oh, and about the color of medieval eggs: common wisdom is that they were probably brown or speckled. P'feh! Take another look at those paintings. See any brown eggs? Me neither. If you find a painting of medieval eggs that show them to be any color other than white, I'd love to see it.