The honey acted as a preservative.
Apicius: “Gather them carefully with their stalks and put them in honey so that they do not touch each other. Choose faultless quinces with their twigs and leaves, and put them in a receptacle, and pour over honey and defritum; you will keep them for a long time.”
The principle, and the name, are thought by some food historians to have evolved into British marmalade.
Pleuvier, Liliane. “Jams, Jellies, and Preserves.” in: Lafleur, Mark, et al. Encyclopedia of Food and Culture. New York: Scribner. 2003.
Plouvier, Liliane. L’Europe se met a table. DG Education et Culture, Initiative Connect lancée par la Commission européenne et le Parlement européen. Brussels, 2000.