Explanation: One of the favorite sweeteners of Romans was a concoction called defrutum, which was ~~wine~~ grape juice, apparently, boiled down into a sweet syrup. Sounds harmless enough, right?
Well, it was boiled down into syrup in lead vessels. Specifically, lead vessels, because copper and iron alloys left an aftertaste; whereas lead reacted with the wine and made the resulting syrup sweeter.
What's worse, the Romans knew lead was unhealthy, both short and long-term.
But hell, what were the rich supposed to do?! Eat their fancy fruit and ice desserts without additional sweeteners??