Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is there a specific length of time for cold process saponification?

  1. Dec 19, 2009 #1
    There are often posts on the soapmaking forums about using one's own soap before it is cured. Curing time for soaps made with oils that solidify at room temperature is four to six weeks. For 100% Castille (olive oil) or similar, the curing time is six months or longer.

    Of course, we all test our own soaps after a few days.

    Does the amount of water used increase or decrease the length of time needed for saponification?

    It is standard practice to use less water for soft oils, one part lye and one part water, so that the soap will come to trace more quickly. (Trace is when the soap is the consistency of soft custard, identified by the traces left on the soap when one drizzles it onto the top of the mixture in the pot.) Soap must reach trace in order to put it into the mold. When using more water, for ex.: 1 lye to 1 1/2 water, it can take ten hours for Castille soap to come to trace when hand stirring. (Many use immersion blenders, which is faster.)

    Could someone spell this out for me? There are many questions about it on the soap forums.

    Thank you very much!
  2. jcsd
  3. Dec 19, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It is likely that the more fluid the early trace, the more tendency it has to break the emulsion. This would correlate with the amount of water added. I would expect this to be more of a problem with soft oils (higher percentage of unsaturate) as well since their more open structure would let the water phase migrate more easily. Adding in a little soap from a previous batch to the new batch should help in the early emulsification step and might stabilize the trace. You might even try a bit of a more purely saturated soap such as coconut or palm. Mineral thickeners (clay) should help as well.

    More water also thins out the lye concentration and reduces the rate of saponification. And it is that rate of saponification that is the primary parameter that determines the trace point.
  4. Dec 19, 2009 #3
    Chemisttree, thanks very much for your explanation. Some do pour into molds at very early trace. I have done it once, and that is the Castille-castor that developed so much ash and went rancid. (That is also the batch I left uncovered.)

    I may try a few bits of soap from the same recipe in a batch.

    I don't use coconut as I find coconut soaps irritating, but I will pass on the suggestion.

    Do you mean palm or palm kernel?

    How would clay speed saponification?

    I hope you don't mind so many questions. I really appreciate your help.
    Last edited: Dec 19, 2009
  5. Dec 21, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Clay and other mineral thickeners help to stabilize the trace... keep it from oiling out. This helps maintain a finely-divided emulsion and that is what you want. Remember that the reaction is occuring at the interface of the oil and water phase. A more finely-divided emulsion has the maximum surface area between these two phases. It is why the stick blenders help in achieving early trace. That homogenation/emulsification step increases the interfacial area between the phases which is what you want.
  6. Dec 21, 2009 #5
    Chemisttree, thank you! It'll be interesting to use the clay and see what it does.
  7. Nov 10, 2010 #6
    Chemisttree, I ended up using a ratio of 1:1 for lye:water, and soaping at room temperature, which has made the whole process simple and easy. It works splendidly for the Castile and olive-castor soaps. I never did join the stick-blender folks, and still stir with a slotted, stainless steel spoon.

    Thank you very much for taking the time to post so much help. Your explanations and suggestions have been most useful. I appreciate it.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Is there a specific length of time for cold process saponification?