Mixing CP soap by shaking bottles

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Oct 12, 2023
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Rural, Texas

I recently picked up Dunn's Scientific Soapmaking and he recommended mixing soap in polypropylene (PP) plastic bottles for small batches instead of going at it with a stick blender in a bowl or crockpot. The good news is that it worked! I made several different single oil soaps this way, 1 bar each (looking forward to sharing the results with everyone later).

The bad news is I have a bunch of dirty soap mixing bottles. They have hardened soap all over them or oily greasy feeling scum coating the inside. Some of it is in the bottle lip, which is really annoying. Using hot water and soap, they still have this oily feel to them where I couldn't clean them that well.

I wanted to ask if anyone could share their tips on how they do their clean up. Are there any cleaning agents you use? Do you soak your dirty soap stuff? Do you try to clean things right away?



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For anyone curious, here was the procedure

Pre-mixed 50.0% NaOH solution in a big 5L carboy (container with a spigot).

I preheated the oil, lye solution, and DI water in a roaster oven set to 135-145 F (measured using a probe since the dial runs hot). It was 40-60 F out, so stuff I took out did cool down. Some things I had to heat or re-heat in the microwave at 30s intervals. The small lye amounts I did at 15s intervals. The lids were all kept loose during heat so nothing went boom.

After preheating, I would weigh the oil into a 1000mL soap mixing bottle. Then I would optionally add water. Afterwards, I would weigh the lye into the bottle, cap it, and shake vigorously for 20-60s. I would uncap, pour into the mold, and then measure the pour temp. I placed the mold into the roaster oven and turned it off after 4 hours. The next day, I took the soap bars out of the mold.

Single oil soaps

OilOil Weight50.0% NaOH solutionExtra waterPour temp
Coconut99.96g35.15g17.52g100.2 F
Avocado100.00g25.19g107.2 F
Extra Virgin Olive100.01g26.15g101.1 F
Palm (attempt 1)99.96g26.99g13.53g115.3 F
Palm (attempt 2)100.06g29.75g !13.55g123 F
Castor (attempt 1)99.97g25.08g116.9 F
Castor (attempt 2)100.03g25.00g127 F

General notes:
  • Pour temps varied. Depends on how long I shook the bottle for and what the original temps were. Oils have different properties and react differently.
  • Oils have different densities, so some soaps filled up my mold and others I didn't have enough. I used 100mL single bar molds.

This was easy to work with and not intimidating. I'm looking forward to seeing it's ability to lather/bubble that everyone keeps talking about.

It's in the oleic family. I want to see how it compares against the olive oil.

Extra Virgin Olive Oil
Everybody touts this as a gentle soap with a non-impressive lather. I'm interested to see how this will compare against pomace olive oil soap.

I'm not a big fan of palm oil for sustainability concerns. That and my true interest is in body wash, so its hardness qualities that it is touted for aren't a big draw for me.

Man, this reacted quick! My first time, I kept shaking past trace and it was difficult to pour out. The second time, I accidentally added too much lye. Another day, palm oil, I'll get you.

I don't think anyone makes 100% castor oil bars besides as an experiment.

First attempt, it didn't pour well, might have gone past trace.
The second attempt I might have preheated my oils/lye water to be too hot (as indicated by the pour temp), which is probably why it looks all messed up.

This is precisely why I avoid any soap making techniques that use plastic bottles. I think they would be a nightmare to clean out. Some people line them with a thin plastic bag so that they can discard the bag and finish up with a clean bottle.
I am not happy cleaning the mess I've made. So far I've soaked overnight and it's been pretty meh making the cleaning easier. I think a dishwasher might work well but I don't have one.

I did really like only using small amounts to make a single bar of soap. I don't think I would have been able to do batches this small with a stick blender.
That’s the best looking experimental castor oil soap I’ve seen. I gave up on palm. Aside from the sustainability issues it always misbehaves if I try to use it at more than 30-35% of the fats.

As for cleaning the bottles, try hot, hot water. After 24 hours or more, I put my squeeze bottles in a big pot of water on the stove and heat the water to 180 or 190 F. The soap dissolves/melts away pretty easily. My next step is to clean the inside of each bottle with a silicone bottle brush and Dawn and the outside of each bottle with a microfiber cloth. Then I rinse/wipe everything down with 91% isopropyl that I keep in a spray bottle. I have hard water and the IPA has the added benefit of banishing hard water spots.
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@BodyWasher ,what a great way to test out new recipes! Sounds like Mobjack Bay has really good advice above on cleaning plastic. I'm sure you've also read on the forum that some people put their containers to the side for 3 days, so the residue turns to soap and then wash the containers.
Good point about waiting to wash @Nona'sFarm. I edited my last response to make it clear that I wait at least 24 hours before I clean my soapy squeeze bottle.

Will also add that after the inside of a bottle has been washed and deemed clean (and still a bit wet from the rinse water), I spritz the inside lightly with the IPA, and then turn the bottle upside down to drain. I think this step is important for draining away any hard water minerals.
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If it's soap that's in the bottle, why not just add water, shake it up, and then leave it to use when you wash your hands. If you shake it up frequently, the soap will be put to good use and the bottle will get cleaned. Granted, it may take a little time. Then, if you decide to use this method again, line the bottle with a bag that can be thrown away after use.
I'm super fascinated with this right now. Reading his book as well and planning to dive into some experiments soon. Wanting to record them so well see how it goes.

Hi, Nice project. Alot of people use. The pillow type packing. To line their bottles.
I wonder if bottle liners for baby bottles would work? Not sure if the plastic is right for it.
for the oily residue, I really love using Dawn Powerwash spray. It really does a great job on oil/grease.
It can be made with rubbing alcohol, dawn dish soap, and water. (plenty of refill recipes online)
Wow i must have been living under a rock because i never knew that Dawn powerwash was a different formula from watered down Dawn. I just ordered one so i have the foamy sprayer too, it looks promising 👍
Wow i must have been living under a rock because i never knew that Dawn powerwash was a different formula from watered down Dawn. I just ordered one so i have the foamy sprayer too, it looks promising 👍
it really works wonders on all of my greasy pans etc in the kitchen. I spray and let it soak for a bit, then wipe up with a paper towel if it's really greasy, then wash as usual. I save a lot of money by making my own refills. I just reuse the pump sprayer. :thumbs:
I reuse packing pillows to line squeeze bottles, which works well for batter that is already emulsified. I'm not sure how well they would work when trying to mix lye solution and oils and shake to achieve trace. I would look for wide mouth squeeze bottles - you can scrape them out pretty well with a spatula. I would either wash them after using, or fill with water if letting sit.