Making Greek yogurt at home is actually quite simple: Spoon regular yogurt into cheesecloth and place it over a bowl for several hours. The strained yogurt is thick and smooth, the cloudy liquid runoff pools in the bowl. Commercial Greek yogurt production starts with milk, but the byproduct, known as whey, is still produced in droves. Whey may look like it should be dumped down the drain, but it's bursting with properties that do a lot more than make yogurt runny. With some processing, whey can be transformed into a substance called bio-oil, which could eventually be used to make jet fuel.

According to a study published in Joule, when Greek yogurt is produced manufacturers use about three cups of milk to produce one cup of Greek yogurt. Considering the high demand for Greek yogurt, this process creates massive quantities of whey. Some Greek yogurt producers attempt to monetize their whey by extracting sugars from the substance or creating protein supplements. While there is a great supply of whey, there’s not much demand, and so much of the substance is wasted. 

In an attempt to use up the whey, they successfully found that by mixing the substance with several species of bacteria and lightly heating it, it can be converted into useful medium-chain carboxylic acids. These MCCAs, called bio-oil, can be used as a precursor for biofuel, a more sustainable biological alternative to geological fuels like coal and petroleum. With further processing and refining, the bio-oils could someday be used to fuel planes. 

Currently, the bio-oil made from whey can be used in livestock feed. The study notes that the acids in bio-oil act as green antimicrobials—essentially a natural antibiotic—when fed to animals. If livestock are no longer regularly fed antibiotics, the number of drug-resistant diseases among animals (especially those that can be spread to humans) could be reduced. 

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Hopefully, the results of this study will encourage companies to invest in producing bio-oil, as it could be an extremely profitable (as well as environmentally sustainable) endeavor. “If our bioreactor system were deployed to address all of this acid whey, more than 8,620 tons of MCCA oil could be produced annually,” the study says. “With a conservative value of $3,750 per ton, this would generate $32MM of revenue per year.”