Tequila-powered cars?

Blue agave can yield almost double the bioethanol per hectare compared to corn ethanol.

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You’ve likely already heard of people filling up their cars with biofuel made from sugarcane, corn, and even leftover oil from fish and chip shops. But what about loading up with biofuel from tequila plants?

A team of scientists at the University of Sydney, University of Exeter and University of Adelaide has found that blue agave (Agave tequilana), the species of agave plant used to make tequila, could offer an environmentally-friendly, low-impact solution to Australia’s transport fuel shortage. 

“In Australia, we have very extreme weather,” said Associate Professor Daniel Tan, an agronomist at the Sydney Institute of Agriculture, in an interview. “We either get floods or we get droughts, so we were looking for a plant that can handle that sort of environment – one that can survive a drought and that will also grow really fast when the rains are abundant.”

The blue agave, which evolved in dry and arid parts of Mexico and can now be found in parts of the United States and central and tropical South America, is a large, sculptural succulent plant that’s characterized by its rosette of thick, spiky, succulent leaves. It can reach over two meters (seven feet) in height, and its immense flower stalks, crowned with small yellow flowers, can extend an additional five meters (16 feet) into the air. The plant grows in rich and sandy soils, and produces a high quantity of sugars, called agavins, in its stem.

For the scientists involved in the project, blue agave seemed an ideal candidate to test out in Australia’s semi-arid interior, where irrigation for more-conventional crops has proven decidedly unsustainable.

“You don’t have to irrigate agave, because it’s almost like a cactus,” said Tan. “So it’s very easy to grow – you plant it and then later on you harvest it, with very little required in the way of inputs.”

To carry out the study, Kendall Corbin, who was a PhD student at the University of Adelaide, undertook chemical analyses of blue agave from a five-year field experiment in Kalamia Estate in northern Queensland, near Ayr. Next, lead author Xiaoyu Yan, a senior lecturer in energy and environment at the University of Exeter in the United Kingdom, conducted a life-cycle assessment of the inputs, impacts and outputs of blue agave cultivation. After that, Tan – who assembled the research team – led an economic analysis of the commercial viability of such a crop in the current Australian context. “It felt a bit like the Lord of the Rings,” he described of the research process – “this fellowship of people in diverse places all coming along and bringing their particular skills on the journey together!” 

A planet-friendly product 

In terms of inputs, impacts, and outputs, the research results were resoundingly positive. The scientists found that the five-year-old blue agave plants they tested could yield around 7,424 liters of bioethanol per hectare each year. The figure compares very favorably to United States corn ethanol, which produces only 3,800 liters per hectare per year. Brazilian sugarcane bioethanol yields are higher – 9,900 liters per hectare per year – but the environmental impacts of agave cultivation and processing are decidedly lower: it uses 69% less water than sugarcane for the same yield, and 46% less water than corn. 

Photo of agave at Kalamia Estate in Northern Queensland. Photo credit to Daniel Tan, who appears in the photo.

Blue agave also outperforms sugarcane and corn on freshwater eutrophication (an excess of nutrients in freshwater ecosystems that can lead to algal blooms, ‘dead zones’ and fish deaths), with 96% and 88% lower impacts, respectively. It also has a minimal impact on marine ecotoxicity (the impacts of toxic substances on marine ecosystems), with 59% less impact than corn and 53% less than sugarcane. Its comparative global warming impact was also significant, at 62% lower than corn and 30% lower than sugarcane.  

Biofuel production in other parts of the world has often been criticized for occupying land that could otherwise be used for growing food. Here, too, agave has an advantage: it grows well on land that’s too dry to use for cultivating food crops, so such an industry would be unlikely to compromise food system security or sustainability in the country. 

“Our analysis highlights the possibilities for bioethanol production from agave grown in semi-arid Australia, causing minimum pressure on food production and water resources,” said Yan in a press release about the research. “The results suggest that bioethanol derived from agave is superior to that from corn and sugarcane in terms of water consumption and quality, greenhouse gas emissions, as well as ethanol output.”

Alongside being used for fuel, the researchers also noted blue agave’s potential as a source of ethanol for health products such as hand sanitizer, which is currently in high demand due to the pandemic.

Does the business case for blue agave bioethanol add up?

However, while the study clearly showed the relative efficiency of agave bioethanol production when stacked up against other common biofuel crops, the researchers concluded that such an enterprise would be unlikely to thrive in the current economic and funding climate.

“The economic analysis suggests that the first generation of bioethanol production from agave is currently not commercially viable without government support,” explained Tan in the press release, “given the recent collapse in the world oil price.” 

“Ten years ago the price of oil was going up a lot, and everyone was looking for a substitute,” Tan added in the interview. “But now it’s going the other way. The price of oil is really low – it’s about half of the global long-term average of 100 US dollars per barrel – and a lot of energy companies have gone broke. Coal-seam gas from the United States is also very cheap at the moment. So it’s a bit more of a challenge now.”

The growth of the electric car industry, and the nascent development of hydrogen fuel cell cars, could also impact on biofuel demand into the future. While the future for bioenergy remains uncertain, at the very least there may be opportunities for some low-food-miles, Mexican-inspired fun in the meantime: Tan said he’s been contacted by a number of companies who are interested in making locally-grown tequila and mezcal (another agave-derived alcoholic beverage).

“A lot of Australian companies are now looking for niche markets where they can add a premium,” he said. “And people will pay a premium for tequila, whereas – unfortunately – I don’t think they’ll pay a premium for bioethanol in their car.”

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