Cure time...

One of the common questions that inexperienced soapers often ask is how can the cure time be reduced? The common response from more experienced soapers is that there are no reliable shortcuts to curing soap.

Part of the curing process involves gradual chemical changes that reduce the pH, increase the mildness, and increase the lathering ability. Another part of the cure involves the physical process of drying which increases the soap's hardness and its useful life and stabilizes the soap's size for ease of packaging.

The drying process can be accelerated some with good ventilation, low humidity, and gentle warmth. The soap must still be allowed to dry slowly enough so internal moisture has enough time to migrate to the surface. If soap dries too fast, the soap can "case harden," which means it develops a hard outer rind that seals the surface and prevents internal moisture from evaporating. The bars may also warp and distort.

I did a simple experiment this May and June to measure the weight loss from two soap bars. I assumed the loss was from water evaporating from the bars.

One soap (all-veg) was made with high-oleic safflower, palm, and coconut oil with a dab of sunflower and castor (listed in order from the most to the least). The water phase was coconut milk and distilled water. I included the fat content in the milk as part of my oil phase and lye calculation. The rest of the coconut milk made up most of the water phase for my recipe. The vegan soap was made with a 30% lye solution concentration.

The other soap (beer-lard) was made from lard, HO safflower, coconut, again with a dab of sunflower and castor (again listed in order from most to least). The water phase was 100% beer, and I used a 33% lye concentration for this soap.

I used a CPOP method to saponify both soaps -- the molded soap was heated at 170 deg F for about 1 hour.

I stored the soaps out in the open on the counter in my bathroom. This bath gets steamy only once a day when DH and I shower; otherwise it gets good air circulation. It is a convenient place to do this experiment and safely out of the way of people and pets. The weather was cool and wet during much of this time. I weighed the soaps on a digital scale that reads to 0.1 gram.

Both soaps showed the same trend in weight loss. There was a big reduction in weight from day 1 (the day the soap was unmolded and cut) through day 14, a moderate loss from day 14 through day 34, and a much slower loss after that. For the math geeks, the data fit a logarithmic trend at R=0.99.

I suspect in the winter with low humidity in the house, the rate of moisture loss might be a little higher. Even so, I would say a good rule of thumb is to allow about a month for moisture levels to stabilize. That doesn't mean the soap is fully cured for the best lather and mildness (see my Post 11 below for more on that), but it does mean the soap won't change much in size and the moisture content will be reasonably stable.

I included the fat content in the milk as part of my oil phase and lye calculation.

how do you do this ? on the soap calculator

DeeAnna, I think this is one of the best summaries I have read on why a long cure is necessary. Your measurements of the actual process is wonderful. Excellent work! :clap:

Robtr31 -- you don't do it in your soap calculator. You create the recipe you want, then do some separate measuring and calculating.

If you make your own coconut milk, you're on your own. I can't help! If you are using purchased coconut milk, I can help. Here's how I figured the amount of coconut oil that was added by my coconut milk:

Read the nutrition statement on the can of coconut milk. Look for two things -- how many servings there are in the can of coconut milk and how many grams of total fat there are in each serving.

Multiply the total servings by the amount of fat per serving. This will give you the total amount of fat in the entire can. Since this is coconut milk, you can safely assume all of the fat is coconut oil. My can of coconut milk contained a total of 45 g of fat. Important: Do not assume the fat in your coconut milk is the same. I looked at a can of coconut milk made by a different company and found it contained almost double the fat that was in the can I actually used.

If the can label tells you the total amount in FLUID OUNCES or MILLILITERS, you will need to weigh the contents of the can. My can contained 400 mL of milk that weighed a total 393 grams. I used the whole can in my soap. The can added 45 grams of fat and 348 grams of mostly water to my soap recipe. (393 g - 45 g fats = 348 g water and other stuff)

I needed a total of 462 grams of water for my recipe. Since 348 grams of mostly water were in the milk, I only added another 114 grams of distilled water. (462 g - 348 g = 114 g)

I needed to add a total of 250 grams of CO, but 45 grams were coming from the milk, so I weighed out another 205 grams of CO. (250 g - 45 g = 205 g)

Hope this helps!

DeeAnna, is there a reason you selected your bathroom for the place where the rate of evaporation was to take place? Just curious. I ask because I recently moved my soaps out of the bathroom for fear that it was hindering the curing process. Now my soaps are located near a dehumidifier with a fan constantly blowing on them.

You assume I am as interested as you in optimizing my cure time, but that's not my focus.

My goal is to gather useful information about my soap in the normal home environment. People don't store and use soap in a dehumidified space with constant air flow. They store soap in a closet, pantry, cupboard, or bathroom and use it in damp or wet spaces.

If my soaps get DOS, so be it. I want that feedback. If it takes a few days longer to stabilize the moisture content, so be it. I want to know that too. If my soaps do fine for me under these conditions, then I know they will be fine for pretty much anyone else.

If and when I ever go commercial (yeah, right!!!! :-?) then I assure you I will use the information I am gathering now to design a lovely and very effective curing space.

Actually, I made no assumptions about your interest in conducting this experiment. I merely asked because I was interested in extending the life of my soap, and yes, maximizing my curing time. But I understand that your experiment has value for those that keep their soap humid conditions, or live in countries where humidity is inescapable. Curing time is important to me and the more I read the less convinced I am that the six week waiting period is as important as most people think. Yes, I agree that the longer you wait the better the soap will be, but not all soaps are created equal and depending on your lye, water and oil mixture I feel the curing time can be shaved off by a couple of weeks in many cases. I can't ask you to repeat your experiment, but I hope that someone will conduct the same experiment with a control group in non damp conditions. Who knows? It may put a end to the question of " how long does a soap need to cure?" I do thank you for your efforts in bringing light to curing times in damp conditions. I know it has helped me immensely.

IMO the cure question has already been answered, and DeeAnna's experiment just proves it all the more. Soapmakers have been experimenting and perfecting their methods for eons. I started soapmaking 10+ years ago with all HP so I could use it the next day. But now I let my soap cure, and it is better soap for it, whether HP or CP. That is the "proof" I need.

Still, experimenting is fun. So go ahead and try various cure and non-cure senarios. I'm sure the answers will be interesting (and probably re-inforcing!)

Ruthie; I too have been making soap for many years, and I agree with the premise that a longer curing time will make a better soap. However I believe the ingredients used dictate the curing time necessary. There comes a time in the curing cycle where time in curing has a minimal effect in curing. I have found that 3 to 4 weeks is a reasonable curing time for the soaps. Given that, I tend to stay away from soft oils and use Coconut oil in my recipes. Coconut oil is great as it has been shown to ****** DOS. I have no scientific proof that keeping a soap in a non humid environment and away from heat will expedite curing times, but it just makes sense to me. I recently purchased a dehumidifier and expect it to be an asset when it comes to helping with the evaporation process. The one thing that is obvious to me is that there is no consensus on how long soap needs to cure. But without a truly scientific study for measuring the curing time for every possible ingredient and oil combination, any evidence provided is anecdotal at best.

Well I'm convinced...I'm off to put some of my new batch in the bathroom! Let you know what happens.

Here is an edited version of something I posted in another thread that expands on the idea of cure being more than water evaporation --

Any solid soap needs time for three things to happen -- to finish saponifying, to evaporate excess water, and to develop a crystal structure. Even if your recipe is designed to make a long lasting, mild, lathery bar, you will see the best of these qualities when you use a soap that is given enough time to fully cure.

The first aspect of cure is to complete the last lingering bits of saponification. When you unmold a soap, the saponification might be 99.9% done, but it's good to allow that last 0.1% time to finish before using the soap. Anyone who has eagerly bathed with a freshly cut bar of soap and gotten some skin irritation has learned that lesson. (... Of course I've NEVER done that! ...) A few days should be enough to meet this goal for a properly made soap.

The second aspect of evaporation is the most visible process to us humans. Evaporation causes a bar of soap to lose weight, shrink somewhat in size, increase in hardness, and become somewhat less soluble in water. My first post in this thread talks about this aspect of curing.

The third aspect -- development of crystalline structure -- is a process that most people can't see and so they tend to ignore or discount this as not being important.

The crystal structure of a solid soap is made of soap molecules that tend to join up to form large sheets. (The soap molecules form other shapes as well such as balls and hot dogs, but please bear with my simplification.) Ideally, these sheets stack one on top of the other, just like slices of bread in a triple-decker sandwich.

In this ideal structure, the spaces between the sheets are filled with a alkaline liquid made of water, glycerin, dissolved soap, etc. This liquid is much like the filling in my triple-decker sandwich. Some of the alkalinity of this liquid is a natural consequence of lye soap being lye soap, and some may be bits of excess lye that will be saponified and neutralized during the first days of cure as mentioned above.

When a handcrafted soap is newly made, this soap structure is disorganized (small wonder after being wildly beaten up by a stick blender!) and there is a lot of free liquid floating around. This disorganized situation is a bit like a dry sponge lying in a puddle of water. You want the sponge to soak up the water to clean up the mess, but the process isn't instantaneous -- the sponge first has to get damp and then it can absorb the water. Same with soap -- the alkaline liquid needs to be "soaked up" and trapped within the soap structure, but it takes time at first to create an organized structure that can soak up the liquid.

A crystal structure of sorts is developed in commercial soaps by drying soap flakes under vacuum, extruding the flakes through dies, forcing the soap into a mold under pressure, and sometimes by (French) milling. Commercial soaps are also sometimes also given a certain amount of time to quietly cure on their own. Since we don't normally have the ability to artificially dry, extrude, mold, or mill our handcrafted soaps, our soaps can only be cured by the application of time. Once the soap becomes more crystalline, the alkaline liquid that is naturally a part of soap is trapped within the sheets of soap molecules, and the soap molecules themselves dissolve more slowly when the soap is used (in other words the soap becomes less soluble in water.) The soap thus becomes milder, in that the soap cleanses the skin without making the skin feel overly dry or "tight."

On a related note, the question is sometimes asked -- Does liquid soap needs an equivalent cure? Liquid soap doesn't have a defined crystal structure, and it doesn't need to dry. It's good to let liquid soap (whether it is in paste or diluted form) sit for a few days right after it has been made. This allows the last bits of saponification to finish up. Some soapers also let their diluted soap "sequester" for days to weeks so fine particles can settle out and thus improve the clarity. This is an optional step -- if a liquid soap looks fine, it's perfectly fine to omit this sequestering time.

This is very interesting DeeAnna. Thanks for doing the research and reviving the thread. As always, your explanation makes it so easy to understand.

I was browsing the Dish forum (I don't post there as I find the forum intimidating, generally) and noticed several experienced soapers state that they use a steep water discount and consider their CP soaps cured after just a few days. If anyone mentioned that here, they'd be shot down in flames - I'm wondering why one group of people find that acceptable? I know the water disc will account for a harder bar, at least, but we all know that hard doesn't equate to cured.

Awesome read!
When I started soaping, I learned saponification and water evaporation happened during cure time. I have never heard that cure time also involves the formation of a crystalline structure. I guess it goes to show there are always a myriad of things to learn... especially in soap making.
Thanks :-D

"...several experienced soapers state that they use a steep water discount and consider their CP soaps cured after just a few days. If anyone mentioned that here, they'd be shot down in flames..."

I agree -- the "cured in a few days" idea is something that pops up fairly often about CP soap made with concentrated lye solution and also about HP soap. It's weird that these two methods are supposed to give similar instant cure, because HP soap usually has MORE water than typical CP soap. I suspect the main assumption is "done saponifying" is the same as "cured." I don't get why this idea persists -- it's a matter that a soaper can easily check by testing a soap every week or three for some months to a year and keep careful notes.

The soaps I tested (see chart in Post 1) were made with lye solution concentrations of 30% (vegan) and 33% (honey beer), so they are moderate "water discount" soaps. You can see for yourself that both took about 30-40 days to really slow down in their weight loss. The longevity in use and lather quality are other qualities of soap that can be easily evaluated. Even though these qualities are somewhat more subjective, it's still possible to learn that a soap can change quite a bit over time.

I think The Gent says it best -- something about a soap that's safe to use is not the same as a soap that is at its best. I think he says it a little more poetically, but I hope you get the drift.

So ... yeah ... I don't get it either, Spenny. :roll:

'Safe to use' does not mean 'good to use'

I think the easiest example is Castile soap - it will stop losing water after a bit of time, but the difference between 1 month, 3 month, 6 month and 12 month old Castile is quite noticeable which means something is clearly happening other than water loss, at least in Castile.

I agree. I just found it odd coming from such experienced soapers. They are sellers, too, so the point was more about them being ready for sale rather than just safe to use, which is kind-of crazy. I'm glad I found this forum first, if I'm honest!

I think this "instant cure" myth is the soaper's version of the classic "get rich quick" scam. Impatient soapers buy into it because it suits them to believe this is really true; the rest of us just wonder about what's going on.

DeeAnna said:

The third aspect -- development of crystalline structure -- is a process that most people can't see and so they tend to ignore or discount this as not being important.
.

Click to expand...

Doesn't gel phase speed up the development of crystalline structure and thus somehow this third aspect needs less time in contrast with a non gelled soap?

Nope. Cure takes the same amount of time for gelled as ungelled. Try it, you will know then.