Floating a burnt piece of toast on top of wine was actually a way to take away some of its bitterness and acidity in ancient Greek and Roman times. The wine was far from as good as what we enjoy today and the charcoal tempered the wine's acidity. The word toast actually come from the Latin word tostum, meaning to burn or scorch.
The term “toast” came from Italy where the ancient Romans placed a slice of toasted bread in wine to signify and celebrate good luck.