Comment by adrian_b

While some had indeed the very bad idea of using lead vessels for boiling the juice, both because lead vessels were cheaper and because that might have enhanced the sweetness, due to the taste of lead acetate, it is unlikely that this was a widespread practice.

Grape juice concentrated and sterilized by boiling has been used for millennia as the main sweetener instead of the more expensive honey, and in most cases the vessels used for boiling must have been made of healthier materials, e.g. bronze in the more ancient times, then cheaper brass during the Roman times.

In the warmer countries of the Middle East, boiled concentrated date juice was used instead of grape juice.