Well your going to wish you weren't so curious with this one. Source of this information: several museum visits around 30 years ago after a pint or three, so the info might be warped.

Gin is a double-distilled 40% or higher spirit flavored with juniper + other flavors.

The source of the alcohol was any carbohydrate or starch source. Whatever was cheapest. It was mostly wheat and barley at the time but just about anything else cheap could be used like rye, turnips, etc. For the cheapest rotgut the ingredients was stuff considered unfit for animal feed (rodent feces, insect damage, molds, water damage, etc).

Since their ingredients were highly questionable, their input cost was minimal. Heating was from coal. They also started making larger batches which further reduced down the cost.

Logistics - Canals at this time period was the most important logistic. One donkey pulling a barge could move as much as 50 wagons. Tons of goods were transported cheaply and efficiently on the barges. The gin was shipped in casks/barrels like beer/ale. Bottles were very expensive and reserved for the elite.

Public sanitation consisted of a gutter on the side of the road. The entire city smelled like the open sewer it was.

The gin was not served in bottles. It was served like beer or ale into cups/mugs/communal tankards etc .. mostly earthenware, leather or wood.