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David Fisher

Mailbag Monday - How Long Does My Soap Need to Cure?

By December 13, 2010

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bars of soap drying
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Cheryl writes, "I was wondering how long these bars have to sit before we can use them. I realize they have to be cut right away, and know the cure times for the lye , but things must change for the drying time...."

In this particular question, Cheryl was asking about the cure time for salt soap bars. Salt soap gets hard in just a couple of hours and needs to be cut right away. But Cheryl is right to ask about the cure time. However, the answer really applies to all soap, not just salt soap bars. Most soap making books or tutorials will say to allow your soap to cure for several weeks before you use it. And for the most part, they're right. But not really for the reason you'd expect.

Cure has two purposes:

  1. To allow the saponification process time to complete
  2. To allow the water in the soap to evaporate out

That's pretty much it. The saponification process is complete in about 24-48 hours. Which means your soap, including your salt soap bars, are safe and just fine to use after a day or two. HOWEVER, just because the soap is safe to use, doesn't mean that it's reached its peak yet. Soap really does benefit from a cure of a few weeks. The water evaporates out and the soap just seems to get a bit better. It seems a bit milder, lathers better and lasts longer in the shower. After a month or so, you're not going to see too much more added quality - but letting your soap cure for those extra few weeks really does make a difference.

So what do I do with my soap? I'll confess. I usually take a bar out of the batch after a day or two and use it - just to test out how much I like the fragrance. Then I let the rest of the batch cure for a month or so before putting it into the "good to use" soap drawer.

For more information about Mailbag Monday - or to send me a question - visit All About Mailbag Monday.

Mailbag Monday is a feature on the site where I share readers' questions and the answers. You can ask questions about candle making, soap making, or any of the related crafts that we engage in. Just email me with "Mailbag Monday" in the subject line. You can also check out previous questions I've answered in the Mailbag Monday Archive.

Comments

December 15, 2010 at 2:07 pm
(1) Ana F. says:

Dear David. I have a query regarding cure and ph that I cannot get answered, no matter how much I research: as the soap is a result of the reaction between fat acids and a base, if the quantities of the oils (acid) and the soda (base) are well balanced, its ph must be neutral when the saponification is complete, as the acids and the base neutralize each other. If the balance is not perfect, the soap should be basic when there is too much (loose) soda, or should be slightly acid when there is too much (loose) oil is that so? As we make the soap with loose oil, the final result after the saponification is complete should be a slightly acid or neutral soap (for the loose acid can be so little that it’s hardly noticed). So, if the saponification is complete after 2 days, why does the soap have a high ph, more than 10? And why does the ph lowers as the time passes and the soap cures? If the saponification is complete there should be no more reaction in this field. And why does it not lower more than 8 most of the times? Can you give me you opinion on this? Thank you for your patience and best regards. Ana F.

December 15, 2010 at 6:52 pm
(2) Beth L. says:

Hi David!
Yes, I am wondering about PH as well. Specifically testing your bars for safety.

I have used phenolphthalein to test by dropping it in a solution of the dissolved(-ish) soap in a alcohol/water.

When doing it this way all my soaps turn a decent variation of magenta (not “red”, but not “pale pink” either). This has happened with my new batches and with some that are 4+ months old (that we’ve been using and seem fine) and even with the batches made in the class I took to learn soapmaking.

I am so confused. Does handmade/ hard bar soap always have a PH high enough to cause Phenolphthalein to react? How do you truly tell your soap is safe and came out all right?

December 28, 2010 at 12:16 pm
(3) David Fisher says:

Great questions!

The oils and lye do “neutralize” each other…but the final product – the soap – (chemically, it’s called a “salt”) isn’t actually neutral. Think of it more of a “recombination of ingredients” rather than “neutralization.” The lye and oils break apart and recombine into soap and glycerine.

Soap is going to be somewhere in a ph range of 9 or 10. The extra oils in the soap aren’t going to have enough acidic power to make a difference. 9 or 10 is just fine for regular real soap.

99% of the saponification, and hence, the ph change, is done with after about 24-48 hours. After that, the soap will dry out as it cures, and it does tend to get a bit more mild, but I don’t believe that the actual ph changes.

Hope that helps!

October 17, 2011 at 6:27 am
(4) Barb says:

Hi David.. but what about goat’s milk soaps? Does subbing goat’s milk for some or all of the water affect the ph of the cured soap?

October 17, 2011 at 7:02 pm
(5) candleandsoap says:

It might a tiny bit…in that the extra fat contributed by the milk might add a little bit more “acid” to the mix…(if you didn’t adjust your lye discount to compensate for it)…but the difference would be very small…if measurable at all.

January 31, 2014 at 4:48 pm
(6) Monica says:

Hello,

Here is my question; how long do I need to let the soap cure before I can package it and mail it to people? I know it should cure for 3-4 weeks but can I mail it before that?

Thank you!

February 1, 2014 at 11:19 am
(7) candleandsoap says:

Soap is safe to use after 24-48 hours – depending on the temperatures you mix at and if it goes through a gel stage or not. All that’s needed for it to be safe is the saponification process to be complete. So…you can package and mail it safely. As it cures, however, it’s going to lose more water, which means it will shrink a bit – so any packaging you may have tightly wrapped around it will now be loose. If your packaging isn’t tight…then you should be fine.

March 31, 2014 at 6:22 pm
(8) Pam Prindle says:

Can I leave my soap in a rectangle loaf and cut it as I need it?

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