Most of the recipes out there are about making "gourmet" soap, but you can also make soap from waste fats. You just won't want to use this stuff on your body, because it'll smell a little rancid. The general rule I use is to make the soap "hot" or with excess lye, which helps destroy the odors, and makes the soap more effective against grease.
I learned about soapmaking from a Red Devil lye bottle back in the 80s, and always wanted to do it, but never did.
Today, Red Devil no longer makes pure lye, but the brand "Rooto" does. I got mine from Vermont Outlet, a True Value franchise. It was about $5 for a pound.
The soap recipes on the web used a lot of fat for 16 oz of lye, so I decided to use only half the jar - 8 oz - and scale recipes to fit. I figured I'd have the required fat for that. So I marked halfway down the bottle; you have to open it up and see where the top of the lye is, then go down halfway and mark it.
I made a mistake in scaling recipes, however. I converted ounces of fat to liters of fat. You can't do that -- fat weighs less than water, so volume conversions will not work. You end up with too much fat.
So I had a recipe that said to use (according to my bad calculations) 1.8 L of fat. I took my fat and simmered it a few seconds with water a bit to let the heavy stuff fall into the water. Then I strained it into a jar. I used the cut-off top of a 2-liter bottle as a funnel, and used coffee filters in it.
(At this point, most articles go into what fats to use. Things like "shea butter" and olive oil are popular. Being me, however, I used fat collected from cooking, so it was a mix of vegetable oil, chicken fat, bacon grease, maybe even beef fat. It was all pretty disgustingly rancid as well, because it was saved up in jars for months. The washing helps a little bit. Some articles said rancid fat would make acceptable, if smelly, soap.)
https://www.youtube.com/watch?v=tuzlhMtza1M&feature=youtu.be
Cleaning fat is pretty easy. You ladle the warm fat into the filtered funnel, and wait. As you get to the bottom of the fat, and the top of the water, it'll get harder to keep the water out of the ladle (and the fat will be dirtier). To make it easier to separate, you can pour this blend into a glass cup. The fat will form a thicker layer, and you can pour most of the fat into your ladle, and transfer it to the funnel.
This picture shows the fat is a thick top layer. My oil got a little messed up because I put baking soda into the oil to clean it. I read a web page that said to use baking soda, and it didn't seem to help.
Be careful about temperatures. Don't let it get so hot you can't handle the cup or the pot.
This is a photo of the fat - almost 2 liters, but not quite.
The graduations on the side of the bucket were added by measuring water into the bucket, and marking the level. I did the same with this glass pitcher.
Next, I had to make the lye water. The recipe indicated around 0.8 liters of water, so I poured that much into the pitcher. The recipes generally call for distilled water, but I just used tap. Maybe that's a problem.
Then, I measured out a plate with 8oz (half the jar) of lye. I just kept pouring a little out until the level was where I marked it 8oz on the bottle. Both the lye plate and water jug were taken out to the porch, for mixing. The recipes call for good ventilation, and outdoors is great ventilation.
(Some soapmakers are real uptight about having a set of bowls and pitchers for soapmaking. I don't understand why they do this. Everything is non-porous and you can neutralize the lye with vinegar. Lye is sodium hydroxide - and we all eat sodium, hydrogen, and oxygen. Lye's used to make food, too. So why the paranoia?)
I poured a little bit of the lye in slowly, and mixed it with four disposable chopsticks held together like a whisk. The water got hot pretty quickly, so I let it cool down before adding a little more lye. This process took around 30 minutes, but the water never got too hot.
(Then, I took the plate to the kitchen and rinsed off the remaining lye bits. To neutralize any remaining lye, I poured vinegar over the plate.)
The hot pitcher lye water had to sit nearly an hour before it was cool enough to handle. I let it get to around 120 degrees F, and put it next to the fat bucket so it would transfer some heat. 120 F is almost "too hot to handle". It's too hot for bathing, which should be at around 105 F.
When the temperatures were pretty close, I slowly poured the lye-water into the fat, stirring it together.
https://www.youtube.com/watch?v=WMX0qEL9RjA&feature=youtu.be
This is the mixture after the lye-water's been mixed in. It's like cream-colored oil.
The instructions say to stir 15 minutes to 40 minutes, but I had to stir a lot longer than that to get to a "light trace". (I stirred with those same chopsticks.)
https://www.youtube.com/watch?v=LXdKpaAALtk&feature=youtu.be
At this point, the stench of rancid fat was getting to be too much, so I added some cologne and a bit of ground sage. It had some effect, but not much.
It didn't seem to be the same as "trace" in other videos. So, I eventually heated up some water, and then put the bucket into the warm water and kept mixing until it thickened up a little more. When it got some more body, I figured it could be wrapped up. The bucket was wrapped with a sweatshirt, and left to sit for an hour or so.
It worked. Here's the real trace:
https://www.youtube.com/watch?v=UH0nyUfviKg&feature=youtu.be
The heat and insulation are necessary to carry out the saponification process - where the lye reacts with the fat molecules. The reaction generates heat - and requires heat to continue the process. So some insulation helps the reaction along.
I added more cologne (Carolina Herrerra for men), and mixed it in. Now it finally smelled like something other than rancid fat. It smelled like rancid fat getting ready for a hot date.
I hope I didn't have too much oil and the soap will not leak excess oil.
The soap was wrapped up, in the bucket, for a day, and the chemical reaction continued to generate heat, sending the soap into a "gel" phase. Also, some stuff floated to the top - I suspect it's the stuff mixed with baking soda.
That's a picture of the gel - it's the dark stuff below the white stuff. There's also some nasty brown liquid that's seeped out of the soap. I'm not sure what that is, but it could be lye water.
Once it has hit the gel phase, soapers remove the insulation and let it cool down. This causes the translucent gel to harden and crystalize into a lighter colored, solid substance. It took one day for this to happen.
By the third day, the soap seemed solid, like tofu or a soft cheese, so I tried to pop it out. That didn't work, but squeezing the sides to loosen up the soap mass, and then flipping it over onto newspapers, eventually worked. You just let it sit, and the soap will fall out of the bucket.
The cylinder of soap was sliced into layers. You can do this with a length of dental floss wrapped around the mass, like you're tying a ribbon around the soap, and then pulling the string together. The string will slice evenly.
The big discs were too large, so they got cut into wedges of different size.
After drying for a month, it was clear that the soap had a lot of extra fat that hadn't reacted.
So I grated the soap and reheated it, then put it in a pot, and heated, added a little water, and then added lye. This was producing a very smelly hot process soap that I was hoping would be a little bit caustic. My goal at this point wasn't to make a hand-soap, but a soap to clean the floor.
The hot soap was put into buckets and pans, and hardened quickly. They were broken into chunks and I tested one. It washed a lot "cleaner" than the original soap, but still had some funk to it. So, I didn't use it for a few months, but eventually found a situation where the soap worked.
I had a lump of soap soaking in water, and it turned into a thick gel. This gel, when spread over grease spattered on the stove, softened the grease well. Rubbing the soft soap into the grease seemed to remove most of the grease. The remainder, I scraped with a plastic scrubber.
After many uses, I got used to this soap. It worked well on the floor. It's really hard to explain the difference, but it seems to meld with the grease better than most detergents. It's also less slippery and less smelly.
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