Ok, I've had a few people ask me for an actual tutorial on hot process soap making. Well, I aim to please, so here it is!! If you have no idea what I'm talking about, you can read a kind of intro here.
I'm not very experienced at writing tutorials, so if there's anything you don't understand, PLEASE ask me so I can clarify it for all.
**Disclaimer: I am in no way responsible for any damage, injuries, etc that may come from using lye, crockpots, or anything else in the making of this recipe.** =)
This recipe isn't the most luxurious, but it's still nice and moisturizing and way healthier than most anything you buy in the store. This is also among the easiest, cheapest, and most hypoallergenic soaps you can make. Once you get the actual process down, you can apply it to other soap recipes you find. Soon you'll have fun experimenting with different additives, oils, fragrances, etc and making a wide variety of soaps.
The recipe we are using today calls for:
54 oz olive oil
16 oz distilled water
7 oz lye
essential oils are optional
Start by gathering a few basic supplies. Pictured below are olive oil, distilled water, a scale that weighs to the tenth of an ounce, measuring containers (preferably not plastic), spoons, and lye.
Make sure you get 100% lye (sodium hydroxide). I buy mine at Westlake Ace Hardware. It can be found in the plumbing section with the drain cleaners (a common use for it). Don't worry, once the soap is finished, the lye is fully saponified--that is, it has all reacted with the oils and is now soap and is no longer caustic. *For more on lye, it's history, and its source, scroll to the bottom of the post.
You also need a crock pot, stick blender (unless you like to stir by hand for 2+ hours, nonstop), and a spray bottle filled with half soapy water and half vinegar to neutralize any residual lye in measuring cups, etc.
When the soap is finished, you will need a mold. I use a simple 9x13 lined with wax or parchment paper and sprayed with olive oil.
Start by turning your crock pot on low. Then weigh out 7.0 oz of lye into a glass container (the lye will static cling to plastic). I'm going to assume that you know how to tare your scale and weigh accurately. If you don't, make sure you learn before you begin.
Weigh 16 oz of distilled water into a separate container. 16 oz equals 1 lb. Make sure you're familiar with your scale and its units. You can see here that once mine hits 16 oz, it switches over to pounds and ounces.
Now take your water, lye, and a plastic spoon outside. When you mix lye with water it causes a chemical reaction. Your glass will get hot, so make sure it's sitting securely on a table. It will give off fumes that you don't want to breathe--that's why it's best to do it outside.
IMPORTANT: Pour your lye slowly into the water. Do NOT pour the water into the lye!!!
As you slowly pour the lye into the water, stir with your spoon until it's all added and dissolved. The solution will be milky white. Leave it sit outside for now.
Go back inside and spray the container that had the lye with your soapy water/vinegar mixture to neutralize any lye residue. Also spray your skin anywhere that lye happens to touch.
Now weigh out 54 ounces of olive oil. Unless you're doing it in a very large bowl, you probably won't be able to fit it all into your measuring cup. So be sure to keep track of your math and know how many ounces you've measured! Here you can see that I've weighed out 32 ounces (2 lbs) so far.
Pour the oil into the crockpot, then go outside and get your water/lye solution. It should now be clear.
Carefully add the lye-water to the oil in your crockpot. The lye will sink to the bottom and you can see it starting to react with the oil on the bottom. Neutralize the measuring cup that had the lye/water in it with your soapy water/vinegar mixture.
Get your stick blender and start to blend. Make sure that the blender is fully submerged and not splashing. Also make sure you keep it at an angle so it doesn't suction to the bottom of the crock pot. If you do splash or spill any, make sure to neutralize it with your soapy water/vinegar mixture.
You will blend for 3-5 minutes or so, until it reaches trace. You will know it has reached trace when it's like a thick pudding and somewhat holds shape when you pull the blender out. (Make sure you do not pull the blender out while it's still running, or it will send caustic lye mixture flying everywhere!) This is what trace looks like:
Put the lid on your crock pot and let it cook. Meanwhile, rinse your stick blender with your soapy water/vinegar mixture.
While the soap cooks, prep your mold. I simply put some wax paper or parchment paper across the bottom of a 9x13 pan and spray the whole thing with olive oil.
Now you wait. About 25 minutes into the cook (all times are approximate, as every crock pot cooks at slightly different temperatures), you will start to see the soap wave at the edge. Castile soap doesn't wave as much as other recipes, but you can see it here. (I don't recommend lifting the lid during a cook, but I wanted to show you a good picture.) See how along the left edge it's getting darker, more transparent, and kind of raised?
As it continues to cook, the waves may rise against the lid. With some recipes, the waves may even lift the lid. Here you can see it waving against the lid.
Here's my soap at approximately 45 minutes. You can see that there's still an uncooked island.
10-15 minutes later, and it's all done!! Every recipe cooks at a different time, so especially if you're trying a new recipe, check it often. When the island is gone, stick a spoon down the center of the soap and make sure it's cooked all the way through.
Turn off the crock pot and stir the soap. With some recipes you'll have a nice layer of glycerin on top. Stir it all in. In this recipe, you can see a little bit of glycerin around the left edge. If you plan to add essential oils, let the soap cool for a few minutes then stir them in. If not, you can go ahead and spoon it into your mold now.
Hot process soap is already saponified and thick at this point, so you're not going to get the perfectly smooth molding that you do with cold process. I like mine rustic and rough, so I don't smooth it much.
Now you just wait until it is all opaque. Here's a batch that isn't quite solidified yet.
It takes several hours to fully harden. Once it's all opaque and hardened, it's ready to cut, just a few hours after being made (as opposed to cold process soap that takes weeks to saponify and cure).
Grab the edges of wax paper hanging over the sides and lift it out of the mold. You can cut it with a knife or pastry cutter into whatever size bars you prefer.
Yay! You've now made your own soap! Wasn't that easy?
*ETA: In the comments, a reader asked the following question: why is the lye not dangerous when it turns into soap?
Great question! The simple answer is that once the soap is fully cooked, there is no longer any lye in it! Without bogging you down in chemistry details, an actual chemical reaction occurs between the lye and the oils. Once the soap is finished saponifying, the lye and oils are now chemically changed into soap. I actually superfat my soaps by 5%. That is, I use 5% more oil than needed for the amount of lye I use. This ensures that all of the lye has been transformed, and it leaves extra oils in the soap for extra moisturization.
Lye actually comes from ashes when wood is burned. They discovered it way back when, when they would burn a fire and cook animals over the fire, the lye in the ashes was combining with the lard in the animal fat (which is another kind of oil) and forming soap. Back then, however, they had no way to measure exactly how much lye they were using. That's why if you hear grandmas talking about soap, a lot of times they talk about how it used to burn. It's because there was too much lye to not enough oil, so some of the lye was left unsaponified. Nowadays, we don't have that problem, since we use clean, pure lye--and this why we go by weight, rather than kitchen measuring utensils that aren't as accurate.
Anyway, this is the way our grandmas, great-grandmas, and so on made soap! Only we have so many more options in the choice of oils, and most of us don't use lard (you can make lard soap, but it's not as luxurious as others). And we can conveniently use a crock pot, rather than slaving over a fire. =)
Also, please do NOT just substitute other oils in this recipe. Different oils require different amounts of lye to react with. Some need less, some need more. So if you want to use different oils, please find a proper recipe or use a good lye calculator to determine what ratios you need.