How a Frozen Daiquiri Hangover Inspired London’s First Alcoholic Slushie Pop-Up

Two days into a boozy holiday in New Orleans, Sara Shipley woke up with a Big Gulp cup next to her head.

The woman behind Sister Slush, London's first spiked slushie pop-up, recalls a hazy memory of coming to "with this slushie cup next to my head and having this flashback of the night before being like, 'Oh yeah, we went to that frozen daiquiri bar.' I thought it was such a cool concept, to just go into a bar and order an alcoholic slushie in a massive takeaway cup."

How big are we talking? I ask.

"It was huge," she tells me.

Like, as big as your head? Bigger than your head?

"Yeah, bigger than my head. I just thought that'd do well in London."

Quitting her job to start the slushie business, Shipley registered her own limited company and put the idea of a boozy iced drink pop-up to her friends. They were extremely into it.

"I bounced around a few names," she says. "One was 'Sloshed Puppies,' which I liked but I did think it was a bit too gimmicky and a bit too childlike-sounding. I think also the domain was gone."

Then, she heard a Sister Sledge song on the radio and something clicked.

"It kind of embodies the fact that it's a female-owned company, having the word sister in there," she explains. Sister Slush was born.

In order to make the spiked slushie translate outside of America, Shipley decided she needed to address one problem: sugar.

"I didn't like about (what I remember of) the New Orleans slushie was that it was very sugary and it still tasted very childlike. I wouldn't like to drink stuff like that all the time," she says. "The sugar gets you as high as the alcohol, and I was like, 'If I want to bring that to London, I need to adapt it for a more sophisticated palate here.'"

And so, Shipley set out on the search for sugar-free flavoured syrups.

"I sourced sugar-free strawberry [syrup] and then the orange and mango is 99 percent fruit juice. I was a bit limited because I wasn't using the sugary ones. If I used the sugary ones, I could've had anything and it would've been a lot easier," she says. "The options I had were strawberry, orange and mango, tropical, apple and blackcurrant, and blue raspberry. I wanted the blue raspberry but everyone said no because it was off-putting."

Shipley's test market audience—her friends—thought the artificial blue looked "really toxic" and so blue raspberry was out. For a long time, they still thought the slushies tasted "too sugary for adults to drink."

The solution, Shipley decided, was to start to infuse her own spirits that would cut through the sweetness a little bit.

"I thought a tequila with a chili and a lime would work," she remembers.

After trying a strawberry chili lime tequila slushie, I can attest that it does indeed work. The sharpness of the lime slices through the syrupy strawberry sweetness, while the heat of the chili makes for an exciting mouthfeel when paired with the slushie's iciness.

With their low-sugar syrups, glitter-strewn fresh fruit toppings, and the generous double shot in each slushie, Shipley's concoctions—much like her customers—are a mix of playful and refined.

"I make an Earl Grey gin as well, which is nice mixed with lemon. I do it with a neutral slush so it's like an iced tea," she tells me.

Her three-flavour machine—a shiny, retro-looking contraption—houses strawberry, orange and mango, and neutral flavoured slush. Shipley has spent the summer hauling it all the way across London from her home in Wembley to the Startisans Drinks Market in Covent Garden in the boot of her car. The machine, she tells me, is "really, really heavy".

How many people does it take to carry it?

"Two. I've hired a guy who's really strong and we have to take the top off and then we can carry it," she says. "It's about 75 kilograms without any liquid in it—it's like carrying around a freezer."

While the machine wasn't hard to track down, Shipley did have to look outside London.

"For some reason there's nowhere in London that hires them out for long-term," she says. "It's really weird but it's more of a Northern concept, slush machines. There's loads up north that do rentals. There's one in Chester, there's one in Leeds."

And now, there's a slush machine in London. I ask Shipley what it is about slushies that she thinks the capital's grown-ups will connect with this summer.

"It really speaks to your inner child," she reasons. "I just want people to be kids for a little bit."

This article originally appeared on MUNCHIES in August 2016.