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Making Your Own Biodiesel

When I came across an article in a magazine about making your own biodiesel, my first reaction was “Yeah, right – get out of here!”  However, as I read on, I discovered that it isn’t too hard to do.  It looks to be on about the same level of difficulty as making your own beer, soap, jam or toffee.  In fact, I think making homebrewed beer and wine might be harder.  So I thought that this was such a handy thing to know about that I just had to find out more and pass the knowledge on.

However, before I get onto the recipe, please bear in mind that: (A) I haven’t tried this myself (yet), (B) you need to be really, really careful with all of the ingredients because a lot of them are very corrosive and (C) don’t put straight home-made biodiesel in your engine but mix it with regular stuff from the pump or the result may do something nasty to bits of your engine.  Obviously, you need a diesel-powered vehicle!

Although you could do this project in your kitchen, it’s probably best to do it where you’re not going to be interrupted by cats, dogs or small children, or where idiots are going to mistake your project for something edible.  Caustic soda is seriously nasty stuff.  However, it is used as a drain cleaner and in that horrible spray used for cleaning inside ovens, so it’s not completely incompatible with kitchens.  Gloves are an absolute must and I wouldn’t turn down a mask and goggles if they’re available.

First of all, you need a good source of waste vegetable oil.  If you do your own deep frying, save the oil.  Otherwise, try cafés, restaurants, tuck shops, canteens and takeaway outlets to see if they’ll give or sell you their waste vegetable oil.  If you’re not a heavy user of veggie oil, you could try saving all the little dribbles of oil from your breakfast fried eggs but it’s going to take you ages to build up enough to be useful.  Saturated fat doesn’t work too well, so skimming the fat off the soup or seeing what you can do with fat from a roast isn’t a smart idea.

Two fish and one scoop of chips for me, and  the leftover oil for my car, thanks.

Two fish and one scoop of chips for me, and the leftover oil for my car, thanks.


  • 1 litre of filtered vegetable oil plus 1 mL for titration
  • 200 mL of methanol (this is the hardest ingredient to get hold of)
  • 10 mL isopropyl alcohol (for titration)
  • sodium hydroxide (caustic soda – try a hardware store)
  • water (for the titration)

First comes the titration.  Mix up the caustic soda: 1 gram to 1 litre of water.  To work out how much caustic soda solution you need, put 10 mL of isopropyl alcohol and 1 mL of oil in a beaker.  Use an eyedropper to add the caustic soda 1 mL at a time. Check the pH using litmus paper or one of those testers you get at swimming pool supply places after every mL of caustic soda. When the pH gets to between 8 and 9, you’ve hit the right spot.  Count the number of mL of caustic soda you used and use the following formula to calculate how much you’ll need to make your biodiesel: number of mL + 3.5 = N. N is the number of grams of caustic soda you’ll need for your batch of oil.  Use leftover caustic soda solution for cleaning the drains or making soap (and for goodness sake, label the container with a large warning label!)

Put your vegetable oil into one container and your methanol into another.  Put N grams of caustic soda in a dish.  Now you’re ready to get started.  Make sure that the containers you use are a lot bigger than the amount of oil you’re working with in case things foam up when reacting.  In the article I read, the people used 3-litre plastic bottles for mixing the oil and caustic soda/methanol solution to avoid problems with fumes, shaking the mixtures gently to stir them.  You may or may not need to warm the oil gently – some of the many websites about making biodiesel say you do need to but others don’t.

Step 1 is to stir the caustic soda into the methanol.  Stir well but don’t breathe the fumes in.  Don’t touch the container, either, as this reaction gives off heat.

Step 2 is to carefully add the oil to the soda/methanol mixture.  Stir well again.  Be prepared for the mixture to react.  (My eyebrows went up when I read this instruction – all the soapmaking recipes I’ve read, which also involve caustic soda and fat, tell you to add the caustic soda solution to the oil).

In Step 3, you leave the mixture to settle.  Leaving it overnight is best.  When you come back the next morning, you’ll find a layer of glycerine down the bottom and the biodiesel up the top.  The longer you leave it, the better.

Step 4 is the tricky bit: separating the glycerine from the biodiesel.  Let the glycerine dry out a bit and use it for soap.  The biodiesel goes into your fuel tank.

If you use too much caustic soda, you’ll end up with soap, which isn’t a total disaster!

If you try this, let us know how you get on.

Happy driving,