Cold Process Soap Vs. Hot Process Soapmaking
Reading Time: 6 minutes
Learn about the cold process soap vs. hot process soap and the equipment and ingredients needed for each of the different ways to make soap.
by Kristi Cook
I don’t know about you, but anytime I’m within sniffing distance of handmade soap, I can’t help but load myself down with as many bars as my budget will allow. Sadly, my budget is never as high as I want because I’d like to purchase multiples of every bar the soap maker offers. So, what do I do? I make my own luxurious handcrafted soap at home every chance I get. Fortunately, crafting soap from scratch isn’t expensive or difficult. The hard part is deciding which method to start with, so here’s a little primer on the similarities, differences, and pros and cons of both the cold and the hot processes of soapmaking.
Soap-Making Process
You need three things to make soap: oils and fats, lye, and water. While the science is geekishly interesting, I’ll stick to the basics. Oils and fats are combined with a lye-water solution, which, in turn, creates a chemical reaction called saponification. This process, when properly conducted, leaves no trace of lye behind. Instead, with simple, easily attainable ingredients such as olive oil, cocoa butter, and coconut oil, you’ll be left with a well-crafted soap that’s creamy, lathery, and gentle on the skin.
Each method uses a different temperature and heat source, which directly affects how long the soap must ‘cure,’ or saponify, before its use. The hot process, for example, uses a crockpot or other heat source to cook the batter at a relatively high temperature until saponification is complete. Any superfats and fragrances are then added to the batter, mixed in, and poured into molds for the soap to dry for a day or two. Because saponification is complete, hot process soap may be used as soon as the bar hardens, which may be anywhere between a day or two to a week, but rarely longer.
On the other hand, cold process soap is cooked on the stove at a much lower temperature, which does not allow saponification to be completed in the pot. Instead, the still-caustic batter is poured into a mold where it is insulated with blankets and left to further saponify for 24 to 48 hours before being un-molded, cut into bars, and cured for another 4 to 6 weeks before use. While this wait can be frustrating for many, the extra time it takes to saponify results in a smoother, shinier finish and texture compared to the rougher, more old-fashioned look and feel of the hot process bar.
Soap Making Equipment
As for equipment, both the hot and cold processes use most of the same equipment and ingredients. This means a new soaper can purchase equipment for one process and then move on to the other without wasting equipment. Even better, once both methods are learned, you can easily switch back and forth between processes as needed. This is what I find the most appealing about these two methods, as switching whenever the need arises doesn’t cost extra money.
Don’t invest heavily when purchasing equipment for either process, as many items may be found on the cheap at garage sales or thrift shops. The possible exceptions would be the scale and the stick blender. The accuracy of the scale is a must for properly saponified soaps, and a dead blender means hand stirring hard for an hour or longer. Just don’t use your good kitchen stash because items used in soapmaking should be dedicated to this craft and never reused for food production.
To save even further, both methods use the same types of molds. These come in all shapes and sizes and range from relatively inexpensive to high-end. They can be purchased online or at the local craft store. However, shoe boxes, cake or loaf pans, or any other container with rigid sides will do just as well and are often free.
Equipment for BOTH Processes
- Safety goggles
- Old clothes
- Latex gloves
- Workspace covering — newspapers, paper bags, or plastic table cover
- Kitchen scale — ounces, pounds, and grams
- Gallon-sized pitcher with pour spout
- Small plastic or glass containers
- Rubber spatula
- Stick blender
- Digital thermometer
- Paper towels/rags
- Freezer paper
- Vinegar
- Molds
Additional Equipment for the Cold Process
- Stainless steel or enameled stock pot
- Blanket or towels for wrapping molds
Additional Equipment for the Hot Process
- Crockpot
Soap Making Ingredients
In addition to sharing equipment, each oil or fat selected contributes the same characteristics to the soap regardless of the process, with one exception. For example, some fats, such as lard and palm, contribute to hardness, while castor oil produces a creamy lather. Others perform double duty, as is the case with coconut oil, which creates a hard bar and produces good suds. And oils such as olive and sunflower are selected primarily for their moisturizing qualities. These oils are all saponified regardless of which method is selected.
However, there is an exception to this rule when superfatting a recipe. Superfats are excess oils and fats left behind in the soap that add specific qualities to the bar. In the cold process, all oils are saponified together, and whichever excess oils are left is what superfats the soap — the soaper has little control over which oil ends up being the one left behind. In the hot process, however, superfats are added at the end of the process after all saponification has been completed making it much easier to customize moisturizing fats in the final product.
As for which lye to use, both require the standard sodium hydroxide (NaOH), which most often comes in a flake or beaded form. Steer clear of potassium hydroxide (KOH), which is intended for liquid soap production only. You may need to order online to locate lye, as many hardware and big box stores no longer carry pure lye. However, do not use Draino or the like, as these are not pure lye and contain dangerous chemicals. Make sure to store your lye in a safe spot away from children and pets.
While not necessary, you can include essential oils or fragrance oils in both processes, as well. Essential oils are oils collected from various plants, while fragrance oils are manmade, synthetic formulations. Try to obtain fragrance oils from soapmaking suppliers who provide guidelines as to how much fragrance oil to include in various-sized recipes, as well as whether or not the fragrance is suitable for use in your selected process. However, be aware of the many fragrance options that are only suitable in melt-and-pour soap bases. These fragrances can’t withstand the high temps of either process.
Soapmaking is like any other venture — it can be as simple or as complex as you wish to make it. When first starting out, however, it’s often best to keep things simple for the first several batches as you gradually acquire new skills. Many soapers, myself included, find the cold process easier for first-timers to master as the stages the batter goes through to become soap are slower and more observable than in the hot process.
During this slower process, the soap remains in a thick liquid form upon molding, allowing the ability to add swirls, multiple colors, and even designs at a relatively leisurely pace. In the hot process, however, the batter is so thick and gooey that it’s often difficult to add these special touches to the soap. But don’t be afraid to jump right in with the hot process if that’s where you prefer to start. It all ends up as soap!
A Word About ‘Melt and Pour’
Many first-timers opt to keep things super simple by exploring the more commonly known melt-and-pour option. This option doesn’t require the use of lye nor the addition of fats/oils on the part of the crafter, and is a safe, simple option for basic customization or for those unsure about playing around with lye. Many melt-and-pour bases range from basic castile to milk and honey bases. Many additives, such as fragrances, colorants, and exfoliants, may be added to these bases. However, it often doesn’t take long before the melt and pour feels too limiting to the crafter, and the search for more customizable processes surfaces.
Kristi Cook lives in Arkansas where every year brings something new to her family’s journey for a more sustainable lifestyle. She keeps a flock of laying hens, dairy goats, a rapidly growing apiary, a large garden, and more. When she’s not busy with the critters and veggies, you can find her sharing sustainable living skills through her workshops and articles.
Originally published in the October/September 2024 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.
