A glass of wine in a restaurant frequently costs close to what the entire bottle costs in a shop. The arithmetic behind that gap is unglamorous, and most of it is about risk.
An opened bottle is a bet on the rest of it
Once a bottle is opened for one order, the remaining wine is on a clock. It oxidises over the following days, and whatever does not sell is written off entirely.
The venue therefore prices the first pour to cover the chance that the last two never leave the bottle. The quieter the room, the wider that margin has to be.
Preservation systems using inert gas or vacuum stoppers stretch the window, but they cost money and slow service down. Either way, the expense lands inside the price of the glass.
The divisor matters more than the mark-up
A bottle yields five or six pours depending on the measure a venue has settled on. That divisor is the single largest lever on what any individual glass costs.
A six-pour policy makes each glass cheaper and lets the list run wider, but it leaves almost no room for spillage or a generous hand. Bars that pour by eye lose volume they never charge for.
Measured pourers and lined glasses exist mainly to protect that calculation rather than to police the customer. Across a busy week the difference is substantial.
Overheads arrive before the wine does
Wine carries the same burden as the food: floor staff, laundry, glass polishing and the rent on the room. It simply absorbs a larger share because the mark-up is easier to apply.
Stemware alone is a running cost that never stops. Thin glass shows wine well and breaks readily, and the replacement rate in a busy service is not trivial.
Storage adds to it too, since wine held at a stable temperature occupies space that could be earning money as seating. That cost is invisible on the list but present in every figure on it.
Why by-the-glass lists converge on the same styles
Turnover is the only real defence against waste, so these lists gravitate towards styles that sell steadily. A bottle emptied within a night never has time to fade.
Unusual or expensive wines rarely appear by the glass for exactly that reason. Their audience is too thin to guarantee the bottle finishes before the wine does.
Needle-and-argon devices that draw wine without removing the cork have loosened this at the top end. They are expensive enough that the practice stays confined to serious lists.
The multiple is not applied evenly
Inexpensive bottles usually carry the steepest multiple and costly ones the shallowest. A venue needs a workable cash margin per sale far more than it needs a consistent percentage.
That is why the cheapest option on a list is often the weakest value while something from the middle is not. The absolute margin has been spread more thinly there.
Reading a list inward from both ends tends to find the section a buyer actually cared about. The bottles chosen with enthusiasm are almost never the ones at either extreme.