Must vs Gleukos

Athenaeus,

I'm off to school, so I will try to give a quick answer to your query.

"Gleukos" literally means "New Wine" or simply put "Unfermented grape juice"

The Biblical history is one I am not so familiar with, although debate over holy men and women drinking it and "Not" becoming intoxicated is at the crux of the debate. As you mentioned in your post. Grape juice almost immediately begins to ferment, so alcohol will be present soon after fermentation begins (only one or two days).

Gleukos and Must are basically the same thing, "Pressed grape juice before fermentation"

There is a process in the wine world called "Chaptalization" named after the scientist Jean-Antoine Chaptal in which beet sugar or cane sugar is added before or during fermentation to reach the desired alcohol levels (this is done in cooler climates where the sugar concentration in the grapes is to weak to ensure proper levels of alcohol. I'm not trying to go off subject, so I will tie these two together. In Germany wine makers (not all) keep some "New wine" back and refrigerated. This is called "suss reserve" or " Sweet reserve" this is added to some German wines during fermentation to boost the sugar levels but is not considered Chaptalization because it is natural grape juice or "Must"

This is one of the ways Gleukos was/is used as a sweetener. I will need to study a little in regards to ancient cooks using Gleukos in cooking, but I would hedge they did. I don't know if this short explanation helped you, but I hope it did. Great question :)

You need to leave some room on the top of your fermenter to allow for the rise of the foam during your first fermentation. You really don't want your must to spill over.

And yes, a Suss reserve is added to "kick start"fermentation in some German wines. This is not an uncommon practice.