How I uncovered a potential ancient Rome wine scam

I don't think they replaced the sun-dried raisins with honey, otherwise the honey taste would be a bit too strong, too obvious. Instead my guess is that they used it as an additive in the final product, if the resulting passum was too dry. Because:

1. As the text mentions, there's a shortcut for making passum - to boil the must instead. If the issue was space, time, or labour they'd likely do it instead of relying on yet another parallel culture.
2. Grape sugar content might vary quite a bit from one harvest to another. And yet it you're doing large scale production you want some consistency.

you can do this at home with some grape juice. Even the unfermented version is delicious, it becomes syrupy (andgreat on vanilla ice cream).