Ch179, The still-room
The meaning has changed over the centuries. It used to be for making everything from distilled alcoholic beverages to jams and jellies to medicines to makeup products to soaps. And it used to solely be the domain of the House Keeper. These are traditionally important and time-consuming things to do, so they were entrusted to the highest (female) member of the staff. Or to the lady of the house, if she ran her own household.
By the Victorian era, it was mostly for storing jams and jellies, cakes, tea, and coffee… but also sometimes still used for making wine, brewing beer, or distilling liqueurs. Phantomhive Manor apparently also keeps the fancy tableware for guests here. By then, keeping a still-room was mostly relegated to the duties of a still-room maid, but some households might have kept it as the domain of the House Keeper, particularly if there wasn’t a large staff.
And when I said “kitchens” (plural) in an earlier post, I should have clarified that a manor like this wouldn’t have a single kitchen with all the necessary things in it. They really were typically split into several rooms, each with a specific purpose, and were collectively called “the kitchens”.
It’s cool that Sebastian says the still-room is stocked with stuff to “entertain special guests”, since no one eavesdropping would find that wording odd at all. Of course, you wouldn’t invite those guests to the still-room, but you would typically use nicer dishes to set the table upstairs… and you would offer them the finest preserves, cakes, and beverages you’ve got. Since the Phantomhives are supposedly known for their hospitality, anyone would indeed expect their still-room to be well-stocked.