The smelly, greasy truth about how sustainable aviation fuel is made

Join our reporter as she tags along with a truck driver dumpster-diving for used cooking oil — all in the name of curbing aircraft emissions.

French fries being cooked in a vat of grease
(Hollie Adams/Getty Images)
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NEWARK, N.J. — When I first meet Dale Brittell on a recent chilly morning, he’s waiting just outside of Newark Liberty International Airport in northern New Jersey. Brittell is part of the growing global effort to reduce planet-warming emissions from commercial air travel, and I’ve come to get a front-row seat to the action. When I arrive, however, we don’t head to the runway. We set off down the highway in the cab of Brittell’s tanker truck.

Brittell works for Mahoney Environmental, a company based in Joliet, Illinois. He’s one of hundreds of employees nationwide who collect used cooking oil from some 55,000 kitchens in hotels, sports stadiums, restaurants and food courts, including those inside Newark’s airport. Mahoney’s parent company, the Finnish oil refiner Neste, transforms these swirls of discarded grease and blobs of animal fat into fuel for heavy-duty vehicles and — increasingly — for airplanes. 

According to Neste, the fuel can reduce carbon dioxide emissions from flights by up to 80 percent when compared to fossil jet fuel. 

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We’re getting away from dinosaur oil to recycled oil,” Brittell tells me during our drive in late November, passing trees with yellow, orange and red leaves still clinging to their branches.

A white man with gray hair drives a heavy-duty truck down the road
Dale Brittell collects used cooking oil across New Jersey for Mahoney Environmental. (Maria Gallucci/Canary Media)

Commercial aircraft and business jets contribute roughly 3 percent of annual U.S. greenhouse gas emissions, along with other harmful effects such as warming contrails. Globally, as international air travel approaches pre-pandemic levels, the aviation sector is driving an overall uptick in emissions from the burning of fossil fuels, which hit a record high last year.

Amid mounting pressure from passengers, corporate customers and regulatory agencies, major airlines and plane manufacturers are taking early steps to clean up air travel. Companies are developing aircraft systems that will burn liquid hydrogen in engines or use hydrogen gas in fuel cells. Startups are flight-testing battery-powered planes for regional travel. And virtually every big carrier has promised to invest in and use more sustainable aviation fuel” (SAF) to curb emissions from today’s airplanes. 

Seven types of SAF are approved for drop-in” use in existing jet engines, including fuels derived from forest residues, corn stalks and municipal solid waste. Yet nearly all of the world’s supply comes from just one type of fuel: hydroprocessed esters and fatty acids, known as HEFA, which is primarily made from pork fat, beef tallow, used cooking oil and the gritty, goopy fast-food remnants swishing in the back of Brittell’s truck.

The low-tech nature of this current climate solution for aviation stands in stark contrast to the high-tech future imagined in sleek artist’s renderings, like Airbus’ three-winged hydrogen jet or Eviation’s angular all-electric plane. But those zero-carbon planes are still decades away from replacing today’s passenger jets. And fuel-makers are still years from producing commercial volumes of fuels made with captured carbon dioxide or microbes. 

So when airlines talk about burning cleaner fuel, right now, they’re effectively talking about the contents of a padlocked dumpster kept behind a Buffalo Wild Wings sports bar. 

A large green hose sucks oily liquid out of a large metal container
Brittell vacuums the residues of fried chicken and other fast-food favorites. (Maria Gallucci/Canary Media)

Curious to see it for myself, I arranged to join Brittell on his morning rounds. We visited a half-dozen locations during our four-hour tour, like a series of teeny-tiny oil wells scattered across suburban New Jersey. I left with a distinctive, greasy odor still lingering on my clothes — the smell of success,” as Chris Cooper, president of Neste’s U.S. division, recently put it to me. 

I also saw clearly why experts say that, despite the growing demand, used cooking oil is only the first step on the long path toward decarbonizing aviation.

Why french-fry oil has gone from trash to clean-energy treasure

After I’ve scrambled up into Brittell’s cab at Newark airport, we set off under cloudy skies for the next stop: a small ramen-noodle joint in the township of Cranford. Our oil well, as it were, is a 35-gallon steel drum filled with viscous liquid. 

This one has to be done every other week,” Brittell explains as he gracefully backs the tanker truck into a partially covered parking lot. 

He hops out, slips on a pair of thick rubber gloves and uncoils the 100-foot-long vacuum hose. The oil drum is hidden in a far back corner of the lot, between a parked car and rows of gray gas meters that connect to apartments and businesses in the building. After a few minutes of slurping, Brittell replaces the hose, returns to the driver’s seat and marks the job as completed in his company tablet. 

A white man wearing a black t-shirt and jeans pulls a large green hose from a tanker truck
The tanker truck, which was originally built for cleaning septic systems, can hold 6,500 gallons of liquid. (Maria Gallucci/Canary Media)

Brittell says he started driving big trucks at age 17, waking up at midnight to distribute milk to grocery stores in the Philadelphia area. He began collecting used cooking oil a decade ago for a mom-and-pop operation called Waste Oil Recyclers, which was acquired by Mahoney Environmental in 2017. Three years later, Neste acquired Mahoney to gain access to coveted U.S. waste-oil supplies.

Restaurants actually used to pay companies like Mahoney to come in and haul their used cooking oil away, because it was a waste product,” Dave Kimball, Mahoney’s president and CEO, tells me earlier by phone. Now it’s to the point where we pay restaurants for their oil.”

At a Buffalo Wild Wings in Bridgewater, the greasy remnants of fried chicken and french fries can earn the restaurant roughly $350 per month, depending on current fuel prices.

Jason O’Toole, the general manager, shows us the kitchen’s setup during a brief visit. Beneath rows of bubbling fryers, tubes collect the leftover oil and fat. Cooks churn through about twenty 50-pound boxes of beef tallow per week to fry food. Twice a day, the tubes automatically send the oil outside to a dumpster, which has a sensor on top that remotely informs Mahoney of how full it is and when it needs to be emptied.

The used cooking oil siphoned from back-of-the-building dumpsters is still primarily used to make road fuels, though fuel producers are beginning to shift existing refinery capacity and build new facilities to make sustainable aviation fuel, as well. 

For more than a decade, U.S. programs like the federal Renewable Fuel Standard and California’s Low Carbon Fuel Standard have offered tax credits and other financial incentives to spur production of fossil-fuel alternatives for transportation, with the ultimate goal of reducing the greenhouse gas emissions that spew from the nation’s tailpipes. (However, certain alternatives such as corn-based ethanol and virgin palm and soybean oil may be causing more environmental problems than benefits.)

In past years, U.S. biofuel producers mainly churned out biodiesel, which must be blended with fossil diesel and can only be used in limited quantities because it tends to congeal in cold weather. More recently, producers have started using a different manufacturing process to make HEFA-derived fuel, which is also referred to as renewable diesel” for road vehicles. The fuel is nearly chemically identical to petroleum-based diesel and can be used directly in engines. It also emits less carbon dioxide and fewer air pollutants than fossil diesel or biodiesel when combusted.

A chart showing a steep increase in biofuels production from 2001–2021. The 2021 total was nearly 2.5 billion gallons
(U.S. Energy Information Administration)

With additional steps, HEFA can be made into a fuel that’s compatible with today’s jet engines. Of the 34 renewable diesel plants now operating, under construction or in development in the United States, eight are expected to also produce SAF, according to a recent count by Biodiesel Magazine.

Soaring biofuel demand is drawing interest from nefarious players 

Globally, SAF production is on the rise, with an estimated 80 million gallons made in 2022 — an increase of 200 percent over the previous year, the International Air Transport Association said last December. Spurred primarily by policies like Europe’s ReFuelEU initiative and the United States’ Inflation Reduction Act, the world is poised to hit 8 billion gallons of annual production by 2030.

At that scale, SAF will equal roughly 10 percent of total jet fuel demand — up from only 0.1 percent today. 

As fryer oil and burger grease become boiling-hot commodities, companies like Mahoney and Neste are moving to snap up as many supplies as possible. In 2022 alone, Mahoney more than doubled its workforce to 490 people and acquired five smaller waste-oil collectors to expand its network nationwide, Kimball says. 

The kitchen-oil boom is also drawing interest from thieves, who drive trucks similar to Brittell’s and steal oil from unguarded dumpsters to sell overseas. When we speak in late October, Kimball tells me that a private detective working for Mahoney helped facilitate 11 arrests in the previous three weeks in the New York area. It can be very valuable,” he says of the waste material. In some of these markets, theft can be as high as 30 percent.”

One way to deter theft is to stash the greasy gold inside the kitchen.

Inside a restaurant kitchen, a man points to a large white oil collection tank
Burger King is one of Mahoney’s biggest national clients. (Maria Gallucci/Canary Media)

The next stop on Brittell’s route is a Burger King in the township of South Plainfield. The restaurant keeps a white 200-gallon canister in a storage area beside racks of disposable aprons and gloves and stacks of 5-gallon syrup bags for making fountain drinks. The oil container connects via a pipe to an outdoor portal that only Mahoney can access. We try to keep everything locked up,” Brittell says while en route. That solves a lot of it.”

Counting carbon emissions from SAF itself is tricky math

Brittell pulls into the Burger King parking lot, uncoils the hose and carries it along a narrow strip of mulch between the building and the drive-thru lane. He hoists the hose above his head, connects it to the portal and counts. The hose pulls about a gallon of oil per second, and today the used cooking oil container holds about 70 gallons. A car passes by to place and pick up an order while we wait.

A white man wearing a black t-shirt and jeans connects a green hose to a pipe valve outside a Burger King
Brittell taps a fast-food oil well in suburban New Jersey. (Maria Gallucci/Canary Media)

For Cooper, Neste’s U.S. president, fast-food joints represent a kind of renewable energy source all their own. We don’t believe that HEFA will ever go away,” he says. We know that we’ll always have those comfort foods that we rely on.”

Once Brittell is done with the Burger King tank, we hop in the truck and drive 30 minutes toward Ryland Inn, a former equestrian estate turned event space. We loop past the elegant venue to the less glamorous rear parking lot, where a big brown dumpster sits among piles of PVC pipes and red bricks. Brittell unlocks and lifts the dumpster’s hatch, revealing a pale pink block with dark brown streaks resting on a grate. 

I muse aloud that it looks like a hunk of leftover turkey meat. No, that’s fat,” Brittell says with a laugh. I’m going to say beef fat. Somebody had a big roast; that’s probably the pan drippings.” Elsewhere in the dumpster, globs of indeterminate origin bob in liquidy goo. He vacuums up the mixture, then scrapes the bottom as clean as he can, so all that remains is a thin layer of what resembles reddish gravy.

Our following destination, a restaurant called Gladstone Market, is another 30-minute drive away. Brittell says he’s put 200,000 miles on his tanker truck in the last four years, burning a mix of dinosaur oil” and renewable diesel along the way. 

A man wearing safety gear puts a green hose into a metal dumpster
“Everybody’s got their own kind of oil,” Brittell says. “It really depends on what [food] they’re making.” (Maria Gallucci/Canary Media)

As we cruise down highways and weave through neighborhoods, it’s hard not to wonder about the CO2 we’re pumping into the atmosphere in an effort to produce lower-carbon fuels. As it turns out, this stage represents a relatively small share of the total life-cycle” emissions associated with producing HEFA fuels, says Nik Pavlenko, who leads the fuels program at the International Council on Clean Transportation in Washington, D.C.

Most of the emissions come from processing and converting waste oil and fats into a diesel-like substitute. The HEFA process is energy-intensive and involves the use of hydrogen, which today is primarily made from fossil gas, though it can be produced using renewable electricity and water. Even so, waste-oil-derived fuels overall are still potentially cleaner than conventional diesel. 

By California’s estimates, renewable diesel made from used cooking oil has a life-cycle emissions factor of 15 to 20 grams of CO2 equivalent per megajoule of energy — or roughly one-fifth that of petroleum-based diesel. 

Still, such figures don’t always reflect the full picture when it comes to carbon emissions. If a batch of used cooking oil originally would’ve been made into road fuel but becomes SAF instead, there’s no net benefit for the climate; the emission reductions simply shift from one sector to another. If waste oil that could’ve been used to make animal feed is used for renewable fuels, then feed-makers might turn to virgin vegetable oil, resulting in more emissions from the farming of corn or soy — an effect Pavlenko describes as displacement emissions.” 

Neste's refinery in Porvoo, Finland, handles both fossil fuels and "renewable" feedstocks like used cooking oil. (Neste)

Then there’s the environmental toll of raising and slaughtering chickens and cows to make the food that ultimately leads to the production of fat, oil and grease. The Center for Biological Diversity, an environmental group, raises concerns about increased agricultural pollution and emissions in a 2022 report about what it calls the myth” of sustainable aviation fuel.

Yet when it comes to fueling more commercial flights with used cooking oil, the biggest challenge is that there will never be enough of it to meet aviation’s insatiable thirst for fuel. The world only discards so much french-fry oil and beef fat, and gathering small batches from far-flung kitchens is time-consuming and expensive.

A fuel that would be really promising for 2050 is something that is both available in large quantities, on the scales we need, but also offers those deep carbon savings,” Pavlenko says. Something like waste oil does really well on one of those metrics: greenhouse gas savings. But when it comes to questions of scale, their availability is always going to be highly constrained.”

For its part, Neste says it’s continuing to develop new ways of making aviation fuel, including using municipal solid waste, forest residues and algae. We see step one being the growth of HEFA from waste and residues,” Cooper says, noting that the company aims to have capacity to produce some 515 million gallons of the current SAF type annually by the end of 2023

In the future, the producer envisions making SAF using a power-to-liquids” process — that is, using electricity, water and carbon dioxide to make as much fuel as the aviation industry could ever need.

As future fuels emerge, the slog of sucking up oil will continue

For Brittell, the hand-wringing over aviation’s carbon-free future and the shifting whims of fuel producers doesn’t have much bearing on the work at hand. He still spends 12 hours a day, 60 hours a week popping by restaurants across New Jersey.

A man wearing safety gear puts a hose away on the side of a tanker truck
Brittell caps and replaces the truck's 100-foot-long hose outside a shopping mall. (Maria Gallucci/Canary Media)

There’s always more oil to pick up the next day. It’s never going to end,” he says from the driver’s seat. The trash trucks run day to day no matter what’s coming. It’s the same thing. As long as restaurants are producing oil, we’re gonna go out every day.”

When we reach Gladstone Market, Brittell eases the truck into the narrow gap between the one-story restaurant and a shed overlooking a small creek. This dumpster is wedged between a wooden picket fence and heaps of haphazardly tossed cardboard boxes. After suctioning the top layer of fat globules, a thick layer emerges. 

A man puts a green hose into a black dumpster next to a pile of cardboard boxes
From oil drums to pristine canisters and grimy dumpsters, Brittell cleans them all. (Maria Gallucci/Canary Media)

We call it peanut butter,” Brittell tells me. As the temperature gets colder and colder, it ends up being thicker like this.” The final layer is dark and gritty like wet sand — the crumbs of fried chicken. You can still get oil out of that. We take it all; it doesn’t matter,” Brittell says as he scrapes the bottom of the dumpster clean.

Our final stop is at a Red Robin restaurant at the Rockaway Townsquare mall. From here, I take a taxi to Newark’s train station, smelling faintly like a french fry the whole way back to Brooklyn.

Maria Gallucci is a clean energy reporter at Canary Media, where she covers hard-to-decarbonize sectors and efforts to make the energy transition more affordable and equitable.