There is a soap making method for just about everyone. If it’s something you’d like to try, please read on.
There are four main processes used in making handmade bar-type soap; CP (cold process), HP (hot process), MP (melt & pour), and Rebatch (aka/ RB; Milled or Hand Milled).
All four processes produce amazing bars that can be ideal for any number of circumstances. There are special benefits and challenges with each that we will explore.
Use a Soaper’s Cheat Sheet
To start, let’s look at a quick reference chart to see the main advantages and disadvantages of each. It might not all make sense at first, but don’t worry. You’ll get the full picture quickly as you progress through this article.
| Soap Type | Lye Contact | Time to Make | SAP Time | Cure Time |
| Cold Process | Yes | Under an Hour | 24-48 Hours | 4-6 Weeks |
| Hot Process | Yes | One Hour Plus | 0-12 Hours | 0-1 Week |
| Rebatch | No (usually) | Two Hours Plus | 0-12 Hours | 0-1 Week |
| Melt & Pour | No | Minutes | 0 Hours | 2 Hours +/- |
Use this quick reference table to see the person-hours, risk/complexity, and calendar time needed for making soap via any of the four processes outlined below.
- “Soap Type” refers to the process used to make it.
- “Lye Contact” shows if you will need to work with lye in order to use the process in question. Please note that the only time you should be working with lye when rebatching, is if you are adding oils to fix a lye heavy batch.
- “Time to Make” is a measure of the human interaction time needed to make it (your time).
- “SAP Time” is a measure of how long the saponification process needs to eliminate any lye and become true soap.
- “Cure Time” is how long the soap should harden after it is cut into bars and before it is used. This is to maximize the amount of time the bar lasts.
It will all make sense in the post below. First, however, let’s define “soap making”. Then we can touch on cure time since these are very much a part of the overall discussion.
Soap Making Defined
A lot of people get hung up on this terminology and what is technically considered “making” soap. As a “soaper” (maker) there are two common interpretations as follow…
Number One: In the traditional “from scratch” world, soap making involves the act of combining lye, a liquid solvent and fats/oils in order to induce an organic chemical reaction called saponification (a fancy way of saying “becoming soap.”)
Saponification is the act of the lye solution creating a chemical reaction (basically cooking) the fats and oils. The resulting product is “soap.” There is no question that this is “soap making” in every sense. For some traditional soapers this is the only definition recognized.
Cold Process and Hot Process fall under this Number One definition. This is because you are combining raw ingredients (lye, water, and fats/oils) to induce the saponification process.
Number Two: A second definition of “making” soap lies in the act of creating the final product. That is, the act of combining ready-made (melted) bases with colorants, scents, essential oils, exfoliates and more.
The bases used are already in a saponified state. This means there is no need to mess with lye. You also don’t need to wait weeks for the soap to cure and harden before use.
Melt & Pour and Rebatch both qualify under this definition. This is because you are using base that has already saponified to create your soap. Your efforts in making the soap are dedicated to the final end-product (bar) without creating the raw base used.
How you decide to define “making” is up to you. I can however tell you that there is an ideal situation for every soap making process.
Some of the most successful artisan soap shops do both “from scratch” and melt and pour to great advantage.
How Soap Works – Regardless of the Process
We’ll dive into each of the four processes – but first here’s a quick video to explain the science of how soap works without getting too overly nerdy.
Cold Process (CP)
It’s called cold process because a natural bio-chemical process occurs when the fats and oils combine with the lye solution to complete the saponification* process.
Because it does not require heating and cooling, it is faster to make (combine the oils, lye solution and pour into molds) than the hot process. However, CP soap takes an average of 6 to 8 weeks to harden sufficiently to be a long lasting bar.
CP Benefits:
- It takes only a quarter of the hands-on work time of hot process soap to make.
- It is easy to perform advanced techniques, such as swirling. This is due largely to how fluid the soap is as you pour it.
- CP soap is very fluid when it leaves the pot and can be used in molds that contain a great deal of detail.
- You can use multi-cut wire/string type loaf cutters to slice multiple perfect bars, from a single loaf, in seconds. These cutters use cheese-cutting wire, harp strings and even guitar strings.
CP Challenges:
- You must cut it at just the right time. If it’s too soft, the bars can lose shape. Too hard and it’s difficult to cut. For example, waiting too long to cut a coconut oil loaf will require more force. This could potentially make the slicing tool more difficult to control.
- It takes weeks to properly cure and fully harden into a long-lasting bar. At Good life we let our cold process soap set for a minimum of six weeks to ensure the bar will be hard and long-lasting in the shower.
- The saponification process takes one or more full days, which means that some organic additives, such as lavender buds, can be damaged by the lye and extreme heat.
*Saponification just means “turning into soap”. This is a natural bio-chemical process and NOT artificially chemically induced.
Hot Process
As you can imagine, hot process involves actually cooking the soap in pots after the fats, oils and lye are all combined. Cooking accelerates the saponification process, so the bars are pretty-well cured upon cooling or within a day of so after.
We like to let ours cure for a bit longer when we use hot process, because it helps firm the bar a bit. As a rule we don’t let any HP soap leave the shop unless it has air-cured for ten days to two weeks depending on the oils used.
Please note however that many shops will simply cut and send theirs out a couple days later. I’m told that works too, so experiment and do what works best for you.
HP can me made on a stove-top, in a slow cooker or just about any consistent heat source that delivers between 140ºF and 200ºF (equal to 60ºC and 93ºC, respectively) – more or less, depending on your preferred settings and method. Approximate temperature ranges are as follow:
- Low Temp Hot Process Heat Range = 140ºF to 159ºF
- Medium Temp Hot Process Heat Range = 160ºF to 179ºF
- High Temp Hot Process Heat Range = 180ºF to 200ºF
Insider Tip: There is also a process called “countertop hot process” that involves getting your oils up to about 200ºF and lye to 190ºF+ then combining them after the oil is removed from the heat source.
This is an advanced method that we will cover in another post. For now please note that it carries additional risks and rewards and should not be attempted by anyone new to hot process.
HP Benefits:
- Like cold process, hot process is ideal for using wire multi-bar cutters.
- The saponification is 95% to 100% complete when the soap is done “cooking.” This means the it can be used quicker as It requires far less time to cure. Please see section on “Curing” at the end of this post.
- Because the lye has been neutralize after the soap has “cooked,” hot process soaps can better tolerate organic additives such as herbs and buds as well as essential oils and scents that are temperature sensitive. You just have to allow the mixture to cool enough before adding these in – but not so much that it is too thick to mold.
HP Challenges:
- It takes time to develop an eye and feel for the consistency of the cooking of blended ingredients and where it is in the saponification process (of becoming actual soap).
- It’s easy to ruin batches when just starting out or when multi-tasking and taking your off the pot for a moment too long.
- The soap is typically thick and lumpy when you spoon it into the mold, so HP is not good for use in highly details molds. You can add more water to the mix when cooking, or after cooking just to thin it out – but then that water can take weeks to evaporate out.
Melt & Pour
This is just like it sounds. You melt soap bases that have been previously created and properly cured – and then pour them into molds (just like cold or hot process). You just need to be careful about adding scents and bracers if you plan to re-melt the soap because they can “flash” (boil off).
MP Benefits:
- Melt and pour is easily the fastest possible way to get to a finished usable bar of soap.
- It is very easy to customize with color, scent, clays and exfoliates.
- MP has the consistency of milk when being poured @ full melt. That said, it captures the finest details of any mold.
- Melt and pour bases can be re-melted several times just by adding back in some of the moisture via purified water or liquid glycerin.
MP Challenges:
- Buying pre-made soap bases can be expensive – especially at craft and hobby shops. Try wholesalers like www.bulkapothecary.com, www.wholesalesuppliesplus.com, and www.candlescience.com. Also look for free shipping deals and online coupons for each.
- Some MP bases are loaded with artificial ingredients. Make sure you get “detergent free” IF you want to make natural soap.
- WARNING: String cutters do not work on MP soap. You need to use a solid blade. This can make cutting from a loaf a bit less accurate until you gain skill at cutting.
Rebatching (RB or Hand Milling)
Rebatching soap is the process of taking existing soap and melting it into a new batch using a method similar to hot process. The process is too involved to get into detail in this post, but in short you:
- Grate the soap scraps, bad batch, or whatever – using a cheese grater of cut it into small chunks with a knife.
- Put it in the opt to heat (stovetop or slow cookers work great).
- Add enough liquid, such as purified water, to get all the shavings moist. I usually use about 2 to 3 ounces of liquid per pound of shaved soap – depending on how hard the soap is when I start. Soap that has cured a long time will need closer to 3 ounces of liquid per pound.
- Heat it on a low setting and stir it every hour or as needed until it becomes the consistency you need for the pour. This is usually pretty thick and goopy for me because I don’t like to add in too much liquid if I don’t have to.
- Then add in any scents, exfoliates, etc. as if this is regular hot process.
RB Benefits:
- The same as hot process with the added benefit of saving a batch of soap that you already spent time making and the money that goes with it.
- Rebatching can be used to fix a lye-heavy batch because it did not originally contain enough oil to saponify and use all of the lye. To do this, simply add in the remaining needed oils so it will interact with the lye and become soap.
- Insider Tip: If you add a little extra oil, it’s okay. It is called “superfatting” and helps make a luxurious bar depending on the fat or oil added. Just don’t overdo it 🙂
RB Challenges:
- The same as HP – except no need to work with lye UNLESS you are fixing a batch that was lye-heavy (contained free lye).
- NOTE: If you are rebatching cold process soap that has not fully saponified, there will be some SAP time needed, but as long as the soap is melted at a steady temperature close to 200 degrees Fahrenheit, it should fully saponify during the rebatch just like hot process.
How long does it take soap to cure?
You saw the term “cure” a few times above so let’s better define it now.
First, what do we mean by “cure”? That is important because it has two meanings in the soap world.
- The first refers to how long it takes the lye solution and fats to complete the saponification process (using up the lye to turn the fats to soap).
- The second definition of “cure” means how long it takes the bar of soap to lose most of its moisture and get super hard.
Cold Process Cure Times
- Cold process soap takes the longest to cure from both interpretations. It takes 24 to 48 hours for the lye solution and fats/oils to complete the saponification process to be safe to use (remaining lye in soap can burn the skin.)
- It also takes the longest amount of time for moisture to naturally evaporate – typically four to six weeks after the bars are cut to size.
Hot Process Cure Times
- Hot process soap typically takes between several hours and one day to cure for cutting into bars. This is if the mix is thick and chunky with most of the water already cooked out. If you added water after saponification, or started with extra water, it will take significantly longer to harden.
- Technically it’s supposed to be ready to use upon cutting (meaning safe and hard enough), but I always let it set for some time to ensure 100% of the lye is cooked out.
Insider Tip: I don’t want to EVER risk someone having a less than stellar experience with my product because I was impatient. For this reason, I generally let the individual bars cure in the open air for one to two weeks before I box them up.
Rebatch Curing Time
- Rebatch is identical to hot process in nearly every way when it comes to cure time. The main variant will be in how much liquid you added to the shredded soap to help it liquify.
- The more liquid added, the longer the cure time.
Melt and Pour Curing Time
- Melt and pour is considered fully cured after as soon as the soap is hard in the mold.
- You should wrap it in airtight packaging quickly after hardening so it does not attract outside moisture and appear to “sweat.”
Insider Tip: I also weigh and measure a couple sample bars from each loaf when they are cut – and compare it to when I box them. Even using hot process, which is relatively instant gratification, the bars shrink slightly and lose a bit of water weight (about 1/3 as much as in CP).
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That’s it – Happy soaping!