Discovery of the Americas
Happened VERY late in period. I've heard it said that potatoes and cacao made it to Europe only in the last ten or so years of the rennaisance, and that it took another few years to work out that potatoes when ripe were good for cooking. Tomato and eggplant were both considered to be poinsonous and merely grown as ornamental plants. Eggplants, in fact, gave small, egg-shaped white fruit (thus the name) - it wasn't til *WAY* OOP that they became the big, purple things they are today. Other "new world" fruit or vegetables were basically OOP as well as the Old World was suspicious of these weird new vegetables. Similarly you'll find chocolate is so rare as to be almost non-existent - it wasn't availible in blocks yet, though spiced chocolate drinks were possible in some regions (though also rare).