Such are my priorities when back home in New York: Family first, coffee close behind.

The story behind the zinger was the third big coffee exclusive entrusted to me by James Freeman, a coffee lunatic from Oakland, California who’s progressed from disaffected freelance musician to bi-coastal super-roaster of international renown. I don’t know what it is. I’ve never met Freeman face-to-face. I call him and he tells me things: The origin of the Gibraltar, San Francisco’s cult coffee. The inspiration behind the SG-120, a coffee in a glass of its own. The what, how and why of the zinger.

I raced up to the bar at Blue Bottle and asked the New York barista to make me a zinger. I don’t recall being smug about it.

– A zinger?

– Yes, a zinger. Ever made one?

– Never heard of it.

The zinger, I explained, was an insider’s iced coffee created by his Blue Bottle counterparts in San Francisco to achieve the effect of melted coffee ice cream in a small glass. They made their zingers by filling a Gibraltar glass halfway with cold-brewed, chicory-flavoured New Orleans ice coffee (see Blue Bottle’s recipe) and topping it with half and half (“half cream” in the UK) and a single ice cube. I boasted that I had learned of the zinger from none other Freeman, the boss of his boss.

– James Freeman?

The increasingly skeptical barista made eye contact with a colleague to check my story. The second barista made a face. It wasn’t a sympathetic face. He too knew nothing of the mysterious iced coffee.

At first they refused to make me a zinger for fear of the naughty things I might do with my photos and my suspect claims. But soon they relented if only to shut me up, half-filling a Gibraltar glass with New Orleans iced coffee and a single ice cube and leaving the rest to me. I slowly poured in the half-and-half but unfortunately there was no swirly effect, as there is when milk is added to Blue Bottle’s regular New Orleans ice coffee.

If somehow I hadn’t got the drink right I wasn’t going to let on. I took 73 photos of my zinger from several angles and then savoured the drink in a prolonged series of increasingly noisy sips. I needn’t have bothered. The baristas didn’t so much as look my way. By then they were 100 percent sure I hadn’t even met  Freeman and, maddeningly, they were 100 percent right. If they had no quick response to my zinger I had none to theirs.

It was past the morning rush and my pre-caffeinated eyes coasted halfway through the coffee menu at Blue Bottle Coffee ‘s new Brooklyn roastery before getting stuck onto a road barrier listed only as SG-120. I shifted my gaze into reverse, spotted the familiar signposts espresso and macchiato and tried to make use of all available evidence: If, as I suspected, SG-120 referred in some way to a Japanese video game console, what made it worth an additional 25 or 50 cents?

The barista, bless her heart, did not roll her eyes when I asked her to explain the connection between sega genesis and espresso, nor did she make a joke about it being a tattoo removal cream. The SG-120, she explained, was the model number of the small, delicate Japanese glass in which Blue Bottle served its single-origin mini-lattes. (So I was right: it was Japanese!) Whereas the similarly proportioned coffee made with Retrofit, the house espresso blend, is called a Gibraltar, after the classic Gibraltar glass, those made with beans from a single growing region – in this instance Kintamani, Bali – took the shape and name of a different receptacle.

The SG-120 is printed on the Blue Bottle menu, unlike the unlisted Gibraltar, but it too enjoys a cult status and purposefully obscure origins. Excitedly unpacking a large shipment of brewing equipment and supplies from the highly respected and now wildly popular Japanese glassware company Hario at Blue Bottle’s location in San Francisco’s Mint Plaza (see map), owner James Freeman and his colleagues discovered that the pieces they’d ordered as water glasses were much too small and delicate for that rough-and-tumble purpose. (They probably wanted the SG-300 rock glasses or HPG-300 tumblers). The Hario SG-120s are amongst the world’s lightest, thinnest-lipped, shortest-bottomed shot glasses. They’re perfect for sake.

So what does a coffee bar do with dozens of ethereal sake glasses it can’t use? Freeman observed their 120-millitre (about 4oz) volume was roughly equivalent to that of the Gibraltar glass he was using and thought the SG-120 could be employed to visually differentiate the single-origin Gibraltars from those made from an espresso blend. His wife Caitlin inspected the boxes of Hario glasses and suggested they name the drink after the model number printed on them.

“We couldn’t call it a Gibraltar because it’s not in a Gibraltar,” says Freeman. “That would be wrong.”

An early review of the SG-120, from TheShot, a San Francisco-based coffee blog, was unfavourable: “It felt cheap and almost disposable, and its thinness and materials added no real thermal properties.”

Fair enough. That view, however, overlooks an elegance and simplicity that adds refinement to a quarter-pint latte. When you look at the SG-120 from the side it appears to float. Instead of the liquid taking its shape from its container, your impression is of a glass taking its shape from the swirls of textured milk and espresso within it. Moreover, if the glass is too hot to hold, that reflects a problem with the SG-120’s preparation: The milk should never be that hot.

My affection for the SG-120, especially now that I know what it is and know that it’s safe to drink, is shared by Blue Bottle habitués on both coasts.

“It’s the most stolen item in the shop,” boasts Freeman.

In Milan, the caffè marocchino – essentially a mini-cappuccino dusted with cocoa– has risen to the height of fashion and stayed there. The cortado, the Spanish take on a espresso “cut” with a small quantity of milk, has been assimilated at coffee bars on both sides of the Atlantic. And in San Francisco, the Gibraltar – a mini-latte served in a paneled glass – is a local cult coffee with a growing and now transatlantic following. The gospel of Gibraltar has spread to seminal coffee shops in LA (Intelligentsia) and New York (Café Grumpy), and to Climpson & Sons in London. It’s the coffee of choice at the newest of London’s great independent coffee shops, Dose Espresso, on Long Lane at Smithfield Market. 

The Gibraltar was conceived as a lark and named as something of an inside joke by the esteemed Bay Area (California) roaster Blue Bottle Coffee. Prior to the January 2005 opening of his first coffee kiosk in San Francisco’s Hayes Valley district, owner James Freeman began using the distinctive but cheap glasses he’d bought at a restaurant supply store for his improvised R & D. This research entailed pulling shots of various blends and roasts in the 4 1/2-ounce glasses, topping some with steamed milk and offering samples to the hopefully grateful employees at Dark Garden, a corset shop down the street. These young women knew a good shape when they saw one and quickly developed a fondness for the little lattes and the cute glasses with octagonal paneled bottoms and smooth, rounded tops. The coffee needed a name and barista/roaster Steve Ford, then a colleague of Freeman’s, found inspiration on the packaging for those glasses. Forget Gibraltar the rock, the city or the strait. This “Gibraltar” is

a registered name for a line of tumblers by the American glassware manufacturer Libbey. It is perhaps fortunate Blue Bottle did not buy similar glasses from a popular French manufacturer, otherwise its coffee invention might have taken the name Duralex, which sounds like the brand of a male contraceptive.

Although Blue Bottle has served Gibraltars by the thousands, Freeman has resisted any temptation to put it on his menu. The word-of-mouth status has been seen as part of its allure. Other cafés, like San Francisco’s Ritual Coffee Roasters, where Ford is now head roaster (but not the boss), have felt no compunction about listing it in bold letters alongside their espressos, lattes and cappuccinos. So how does Ford feel, now that his Gibraltar may be destined for the Oxford English Dictionary?

I’ve never really talked about the Gibraltar for publication, partly because I think it was very much of a time and place – that being the Bay Area circa 2005. The fact that I’m talking about it now is mostly because I’ve given up on the original idea. There WAS something special about it back then. Now, it’s just another drink on the menu to me, and like so many cappuccinos, generally prepared poorly or just wrong. Every year people ask about it, so I can track how far the idea has gone, but the fact that it’s all the way in the UK and I have no idea how it got there is disappointing. And not to be too melodramatic, but I feel like the soul of the drink has been lost. It used to be something unique, and now it’s just another piece of fucking latte art.

Any bitterness felt by Freeman is less of the dark-roast variety. He likes the Gibraltar’s appeal as a transitional coffee for latte drinkers ready for something shorter and stronger. (The Gibraltar has less milk than a standard latte but the same amount of espresso.) He’s pleased that it’s served in a glass (though not all cafés use the exact same glass) and therefore can’t be ordered to go. It’s a stick-around coffee which, according to Freeman, fosters cultural experience, the urban use of spaces, and sustainability (no paper to toss out). He’s nevertheless uncomfortable taking or sharing credit for the unintended consequences: “The moral of the story?” asks Freeman. “Be careful what you joke about.”