Hāngi cooking: Grounded in Māori tradition, Ozone is reusing coffee creatively

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With sustainability high on its radar, Ozone Coffee Roasters brings the Māori technique of Hāngi cooking from New Zealand to the UK.

Cooking with coffee isn’t a new thing. Coffee-braised protein is age-old, filter coffee in chilis a modern classic, and ground coffee rubs are commonplace. There’s even a cookbook about it. And let’s not even get into baking. But Ozone Coffee Roasters, originating from New Zealand and one of the UK’s premier specialty roasters, is breaking the mould, rejigging a traditional technique with modern equipment to be more sustainable.

We wanted to try and incorporate a coffee flavour into a dish without actually putting coffee in it,” says Sam Scott, the head chef at Ozone’s London eateries. Enter hāngi. It’s a technique developed by New Zealand’s indigenous people, the Māori, which is essentially “cooking in the ground”.

“A couple of hundred years ago, obviously there were no ovens or gas. They had clay and fire,” explains Scott. “They had to work out how they could incubate a cooking chamber without anything else.” The Māoris dug a large pit in the ground, stacked up a bunch of sticks and placed big river stones on top, with the clay and rocks both being good conductors of heat. 

“They’d light the fire underneath, and then as the fire burns and stones get hot, the inside stays hot for a long period of time,” says Scott. The stones would be placed into the ground with a little water to help it start steaming. Then, flax baskets filled with vegetables and meat would be lowered into the pit, mixed between the rocks, which would be covered with wet sacks and a layer of sheet metal to retain heat and insulate the cook. That would all be topped with the soil that was dug out of the ground, then left for three to four hours.

Scott says it’s a big tradition in New Zealand, and normally only carried out for special occasions: weddings, funerals, leadership meetings, and the like. Pre-European vegetables and local produce were commonplace, like taro, kumāra (sweet potato), and plenty of greens.

The Ozone head chef compares it to modern-day steam baking: “The moisture from the clay, dirt and stones, plus the big wet sacks on top, provide the heat, and the moisture coming out of your vegetables and meat creates the steam that helps it cook.” It leaves a distinct earthy flavour, but the flavour varies depending on the produce used, the depth of the pit — traditionally four to five feet (approximately 1.2m to 1.5m) — how much clay and dirt you have, and so on.

ozone coffee roasters
Photo: Ozone Coffee Roasters

For Ozone, it’s about the coffee. “It’s so traditional back home in New Zealand, but over here, we really want to showcase a little bit of what our background is,” Scott tells me. “We wanted to figure out a way we could use coffee in a dish, and the best way we could incorporate that was with this hāngi technique.”

But how do you replicate an environment that relies heavily upon, well, the environment? After a lot of trial and error, the team at Ozone landed on coffee for its hāngi. But unlike most recipes using coffee, the eatery’s hāngi doesn’t ask for freshly brewed or ground beans. Instead, it relies on spent coffee grounds.

“Once the coffee as a drink has been extracted, we’re after those wet grounds,” explains Scott. The coffee grounds have to be wet, because baking something in dry coffee wouldn’t provide enough steam. “When the grounds are wet, you can really compact everything tightly, and the steam that’s coming out of the vegetables and the coffee all goes together. It takes us about two hours to cook, say, a kilo of beetroots.”

The Kiwi eatery does hāngi on a bake cycle, between 140ºC and 150ºC. “We’ll tightly compact it into a tray, lay the vegetables in it, cover it over with the rest of the coffee, push it down, and that’s how we go forward,” says Scott. “And we only use it maybe once or twice? As soon as they start to dry out, they’re discarded, but the product’s been used for two things instead of just your flat white.”

It’s an interesting way to reuse spent coffee while being that bit more sustainable. Scott notes that veganism is an important conversation in Ozone’s kitchen, and a major goal is to manipulate vegetables, and give them different textures and flavours. By reusing coffee otherwise composted or wasted, the roastery is killing two birds with one stone.

Read our profile of Apostle Coffee, one of UK’s only carbon-neutral coffee companies.

Sustainability is at the heart of the coffee company’s DNA, and it regularly showcases that with innovations like gnocchi made from sourdough scraps, oil extracted from herb stems, and a “vege treacle” derived from reducing a waste vegetable stock. It works with the Sustainable Restaurant Association and Food Made Good to ensure transparency in its supply chain and tackle food waste, and is also in the process of becoming a B-Corp.

The company’s strategy is to try and incorporate food waste back into its dishes. “The biggest issue around sustainability at the moment is plate waste. With all these sharing plates, people’s eyes are too big for their belly,” Scott explains. “They’ll order too much food and then heaps of it comes back, and you can’t re-serve that. The way we’ve been trying to reduce that is just slowly reducing portion sizes — and obviously charging a little bit less.”

The chef says restaurants know how much meat or vegetables or bread people should be eating: “And that’s all good, said and done. But people are still going to order too much; that’s just natural. People want more than they can eat.”

He adds: “Vegetables are a huge part of our menu and we feel if we can reduce the scraps, we’re doing our part to moving forward for the environment. That’s our background, and if we’re not pushing ourselves to be better or more sustainable in any way, then I need to reevaluate my job.”

Between its two eateries in Shoreditch and Hackney, Scott estimates Ozone uses around 1,000kg of spent coffee grounds every year for its hāngi dishes. Add that to the total from the two restaurants in New Zealand, and the waste reused is closer to 1,500kg.

But he admits that Ozone will never get close to a traditional hāngi. “Traditionally, when you steam bake things, you’d use condensation, and when that’s dropping down into stones, meat fats or the vegetable moisture, it would produce a steam of that flavour. It could be 10 different flavours all dripping down into those stones, and that steam is going to create a different flavour to what it started with,” describes Scott, adding: “Unless we dig a pit in the back of Ozone to do it ourselves, we’ll never get there.”

sourdough gnocchi
Photo: Ozone Coffee Roasters

Hāngi has been a mainstay of Ozone’s menu, with root vegetables like potatoes, beets and carrots all getting the steam treatment. But Scott also wants to push boundaries when it comes to plant-based food.

“We have about 16 plates on the menu at any one time. Around one-third to half is vegan, or can be made vegan. But we don’t just serve falafel or whatever,” he says. “I want to make it exciting for vegans to eat. That’s where we’ve really looked to try and improve over the last year: how we can make these vegan plates just gangster. That’s what people want to eat — they want it to be sustainable.”

Read our story on The Fields Beneath, London’s finest all-vegan cafe.

Anay Mridul
Anay Mridul
Anay is journalism graduate from City, University of London, he was a barista for three years, and never shuts up about coffee. He's passionate about coffee, plant-based milk, cooking, eating, veganism, writing about all that, profiling people, and the Oxford Comma. Originally from India, he went vegan in 2020, after attempting (and failing) Veganuary. He believes being environmentally conscious is a basic responsibility, and veganism is the best thing you can do to battle climate change. He gets lost at Whole Foods sometimes.