So, a few days ago I finally did my post on acidifying liquid soap (LS), or, lowering the pH of soap. In that, I touched on a few different methods to garner the same end result, which was not only to lower the pH, but see if soap properties were maintained, such as bubbles and cleaning ability, the latter of which is most important. I originally didn't bother with working with straight citric acid, because we all know how it behaves for the most part. Until I got to thinking back on some of my research. A fellow soap maker, possibly well known even, by the name of Jackie Thompson, is in the process of getting her book released on LS. It will be a breath of fresh air on the topic since Catherine Failor wrote her books on transparent and liquid soap making over 10 years ago. In venturing to Jackie's website, I found it quite sparse on the information side. She did include 2 powerpoint presentations, each containing a slightly different approach to LS making, like Failor did in her book with the paste and alcohol methods. The one thing that both of these presentations have in common that stood out to me, was how she neutralized her soap. Without going into details, she uses citric acid. Nothing special there, except, she used a 25% solution(her presentation says 20%) , so, diluting 1oz citric acid to 4oz water, or a 1:4 acid to water ratio, for ease of recipe resizing. After adding the appropriate amount of solution, based on titration using phenol-p drops until they go clear, she just "skims off the curds". What??!! But, if my memory serves me well, those curds are the freed up fatty acids that we usually worry about needing to be incorporated back into the soap, and solubilized. That's potential superfat material right there. Why would you want to skim that off? Hopefully her book will go into detail about this and it should be released in September. I've already pre-ordered.
So, with all that having pushed forward recently, I decided to give her method of neutralization a go. Only, unlike her, I went for a true neutral, using the last 8-9 ounces of my glycerin method castile that I'd been experimenting with for the last 3 months, on this very topic. I'd already had the solution premade, but I didn't have much left. In this experiment, i used grams instead of my normal ounces, since I was using relatively small amounts of solution. The pH of the sample was already low, sitting a 9 on my pH meter. Going in increments, and skimming the curbs after each addition, I totaled out with 13 grams of solution and stopped there, gaining a pH of 8.57. At such a low concentration with only slight change, I switched gears and started using straight powder, noticing that the solution, of course, watered down the soap. So using my percentage calculator app to make quick of tedious math. I got the amount of citric acid actually in 5 grams of solution, 1.25, and added that as powder. PH went down to 8.26. My impatience got the best of me, and I doubled this amount, adding 2.5 grams of powder, and thus, lowered the pH too far!! I ended up with this giant curd, and this watery liquid with fatty acids I couldn't strain out. And a pH below 7. Down the drain that went. I really need to learn patience.... At any rate, the actually total amount of citric acid used, be it in solution or powder form, was 7 grams(0.2469oz) for 8-9 ounces of soap. I will most definitely use less than that next time, but this does give me a good idea of how much will be needed. Also, and interesting note, I weighed the curds I strained after a 5 gram addition of solution; it weighed 20.4 grams. So it would seem a significant amount of weight can be lost using this method.
I did however learn something else from this method, and it brings me back to one of the other methods I tired. Using citric acid alone in lowering pH of soap causes fatty acids to be released from the potassium molecules in soap, and be replaced by the citric acid, thus creating potassium citrate. I used 2 forms of potassium citrate to lower pH, and yet, neither material worked. The pH hovered around 9, and in some instances, tried to rise a little. What made this so different? I don't think i could google enough to figure this one out sadly, and Kevin Dunn's Caveman Chemistry forum seems pretty dead. This will be looked into further as I go along. I do hope someone could chime in on topic someday.
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