Defrutum is made by boiling down grape juice (called must) in large kettles until it had been reduced by at least half. The sweetest defrutum was further boiled down into an even stronger concentrate called sapa. This is a thick fig syrup. It is used in Pullum Frontonianum, a dish from ancient Rome, found in Apicius, a cookbook from ancient Rome from the 4th or early 5th century, which allegedly written by Marcus Gavius Apicius.
This is how to make defrutum:
- Boil the liquid until reduced by two thirds.
- Let it cool.
- Produces 200 ml (7 fl oz)
It is advised not to use bronze or copper kettle because the metals would react with the acids in the defrutum and give the finished product an unpleasant metallic taste.