Just a minute ago, this oil helped make a delicious meal possible. But now, it’s just some nasty goop. What should we do with it? Well, the easiest thing would be to pour it down the drain; that makes it seem like it’s gone, but it’s not really gone. Instead, it’s collecting bits of food and other random stuff, producing monstrous, greasy blockages that clog not only your own drain but entire sewage systems, causing flooding and pollution. Many places have laws for proper disposal of grease, but we can go one step further. Instead of just throwing it away safely, we can turn it into something useful. And if you’re wondering what anyone could possibly want with a bunch of digusting, used cooking oil, the answer is: biodiesel. You’ve probably heard of diesel engines. They power farming and construction equipment, trucks, buses, ships, trains, backup generators, and even some cars. Most of the fuel that feeds these engines is refined from petroleum, which comes from long-dead dinosaurs and other ancient fossils. But diesel fuel can also be derived from more recently-dead organisms, like plants and animals. And this type of fuel is what we call biodiesel. Biodiesel is a biodegradable energy source, made from plant oils or animal fats, that can usually be burned in regular diesel engines. You guessed it, it’s the ‘bio’ version of diesel. It’s cleaner than normal diesel, so there has been a push to generate it from crops like soybeans. Now, growing plants for fuel, instead of food, comes with its own problems. But fortunately, we already have some oils and fats right here. Preparing your used cooking grease for recycling is easy. First, let it cool down to room temperature. Then, transfer it to a clean container. You can use any old bottles you have lying around, like milk jugs, as long as they’re completely empty, rinsed, and dried. Use a funnel to avoid spills and a sieve to filter out any small food particles. You can even add bacon grease and other animal fats or the excess oil from canned food, like tuna or sardines, just make sure it’s really oil and not brine. So, what happens now that your oil is safely contained? Well, many cities have recycling services that will pick up large amounts of grease from restaurants and other establishments. But there are locations where individuals can drop off their containers, as well. All of this grease will end up at a processing plant, where it can be converted to useable biodiesel. How does this conversion work? Well, all these oils and fats you donated are made up of triglycerides, a glycerol molecule connected to three fatty acid chains. To convert fats to fuel, they react with an alcohol, usually methanol or ethanol, which produces long-chain esters and glycerol. To compare, here are some molecules of regular diesel fuel. Now, here are the molecules we created by breaking apart the triglycerides. Glycerol is the odd man out, so it’s removed at the end of the process. But look at these esters! If you squint, their structures look pretty similar to those of the long-chain hydrocarbons in regular diesel. And diesel engines, with a few small modifications, can also be made to squint and burn these esters like regular diesel fuel. Et voila! Biodiesel. Now, you might be wondering whether all this hassle over recycling used cooking oil is even worth it. After all, how much energy can it possibly generate? Well, if all the grease that New Yorkers throw away in one day were converted to jet fuel, it would be enough to power several hundred flights from New York to Los Angeles. And let’s not forget that using waste oil instead of burning more fossil fuels will limit our negative effects on the environment. Recycling used cooking grease turns goop into good. By contributing a little bit, individuals and businesses can help create an alternative, stable source of diesel oil, while protecting the environment and keeping our cities cleaner. And that’s pretty slick.