Spanish grandmother Francisca, 81, prepares traditional homemade soap.

We spend our lifetimes living and learning, collecting little pearls of wisdom and knowledge that shape the way we think and act and perceive our world.

But sometimes, I think, we forget that the elders in our society have walked these same paths before. They’re like a great beautiful leather-bound book of knowledge just waiting to be cracked open and read. We just have to find the time to honour that wisdom, to seek them out and listen and learn from their stories.

A few months back I spent an afternoon with the grandmother of my friend Juan (y’know, the guy of homemade vegan Nutella fame.)

Grandmother Francisca is 81-years-old and grew up in Spain during the difficult years of civil war and rule under Spanish dictator Francisco Franco. It was a time of using and reusing by necessity because often there simply wasn’t enough to go around.

Francisca now lives in San Vicente, a little town just outside my adopted city of Alicante, along Spain’s southeastern Mediterranean coast. But she grew up in Castilla-La Mancha, that wide, sparsely-populated and windswept plateau dominating Spain’s interior. The region is famed for its proudly no-nonsense yet endlessly hospitable people, and for the bold wines and vast quantities of high-quality olive oil they produce.

Spaniards across this great nation use an astonishing amount of olive oil in their daily lives. They smother their breads and salads in the stuff. They fill heavy-bottomed pans half-full with thick, bubbling layers, then fry their famous tortillas or dunk all kinds of vegetables and meats in the piping hot liquid gold.

Often, they reuse this frying oil, allowing it to infuse with the flavour of meal’s past, until it takes on a deep golden colour, peppered with the crumbs of this and that.

Then, in the old way, this olive oil is recycled some more – into soap.

This is actually the traditional basis of Castile soap, that astoundingly all-purpose soap famed around the world as a natural and biodegradable base for everything from homemade hand washes and laundry detergents to green cleaning products.

It’s one of the oldest soaps known to mankind and is named after the region from which it originates: Francisca’s Castilla-La Mancha.

So naturally, I turned to her to learn the traditional recipe. We sat on her front porch for three hours one afternoon, chatting and laughing while gently stirring a giant red tub of soap by hand with a rough branch fossicked from the garden. (Okay, so Juan did most of the stirring. It’s actually pretty tough work.)

Spanish grandmother Francisca makes homemade Castile soap.

Here’s the recipe Francisca shared with us.

Ingredients

Makes about 60 bars.

5 litres water
5 litres olive oil
1kg lye (caustic soda)

For a smaller batch (makes about 25 bars):

400 millilitres water
2 litres olive oil
220g lye (caustic soda)

Method

If you’re using recycled olive oil, first run it through a sieve to remove any remaining food crumbs.

In a well-ventilated area, add the lye to the water in a sturdy, heat-resistant plastic or stainless steel tub. Allow the mixture to cool for half an hour or so. Be very careful with this step! Never add water to the lye, as it can cause the lye to splatter, erupt, or explode out of the container. Lye in this form is also highly corrosive and can burn your skin, so protect yourself with gloves. Head here for more tips on working safely with lye.

Don’t worry about the caustic element to the lye. As this article explains, when fats like olive oil are combined with lye in proper proportions, a chemical reaction called saponification occurs. The end result is soap plus glycerin, which is all-natural and completely safe to use on your skin.

Pour the olive oil into the cooled lye mixture and begin stirring. Traditional wisdom says you mustn’t stop and should always stir in the same direction.

Continue stirring until the mixture thickens and forms a trace after the stirrer (as in the photo below – kind of like the consistency of honey). This can take a pretty long time by hand (think hours) so swap to a stick blender if you’re short on time. That should only take about 10 minutes, sometimes even less.

Homemade soap reaches the "trace" point during stirring.

Pour the mixture into a large soap mould. We just used a cardboard box lined with old clothing rags. Plastic containers and metal cake tins also work great but you won’t be able to use them for food again in the future.

Homemade soap poured into a mould, ready for drying.

Stand the soap in a dry place until the block hardens. After a week or two (depending on the size of your block), it will be hard enough to chop into smaller blocks for further drying and curing. Be careful as the lye can still be caustic at this stage, so protect yourself with gloves.

You can see in the photo below that the blocks are still quite moist on the inside. They probably need another week or two of drying, until they turn a pale yellowy-white colour all over.

Homemade soap cut into individual bars, ready for curing.

Once completely dry, go ahead and use your all-natural, homemade soap. These bars also form the base of my super-simple homemade laundry detergent.

Homemade soap, dried and cured and ready for use.

Traditional homemade Castile soap, dried and cured and ready for use.

Cold process versus hot process soap making

There’s actually two ways to make your own soap from scratch. This recipe uses the cold process version, which means the bars of soap take about a month to six weeks to completely cure and dry.

There’s also a much-quicker hot version, with the soap bars ready to use in as little as a week. This article explains how to do both processes.

This Castile soap recipe is a great base from which you can play around with all kinds of natural colourings and fragrances. I’m currently having a bunch of fun experimenting with things like turmeric, beetroot, flowers and essential oils.

Francisca makes traditional homemade Castile soap in Spain.

Spanish grandmother Francisca.

Rows of homemade Castile soap, ready for drying.

Completed homemade soap, which makes a great natural laundry detergent base.

And to sign off, I have to say a huge thanks to Juan for sharing his grandmother with me, and an even bigger thanks to Francisca for sharing her wisdom with us all.