Yesterday I was chatting with some soap making friends and this age-old question popped up…
“What is better, hot or cold process soap?” We agreed that hot process is best when needed quickly and a rustic look is appropriate. Cold process is ideal when complex swirls and patterns are needed, and you have a month to wait for curing.
What began as a quick question quickly evolved into a full-blown hour-long conversation about the advantages and disadvantages of hot process verses cold process soap making. A lot of good points evolved throughout the discussion that I will share below.
First, we all recognized that both hot and cold process soap making share some wonderful advantages…
Advantages Common to Hot Process and Cold Process Soap Making
Bar Hardness: Both processes can produce a rock-hard bar of soap that lasts a long time in the shower.
Glycerin Production: Both cold and hot process soaping methods result in soap that produces natural glycerin. Glycerin is the best skin cleanser you can get.
Ingredients: You control 100% of the ingredients that go into the soap. You can use the highest-grade organics or the least expensive oil on the shelf. It is completely up to you.
Cost: This goes right along with ingredients but deserves its own call-out. By controlling everything that goes into the soap – and the quantity of material you purchase in – you have a great opportunity for establishing cost savings.
Super Fatting: It is easy to manage the level of super fatting. (Although control of actual super fat type varies by process).
Bar Usability: You control the bar size and shape, which is important for usability. This is true of every handmade soap making method, but still worth mentioning.
Soap Variety: The varieties and possibilities are endless. You can get a whole new soaping experience just by changing the ratios of oils or substituting. Just be sure to run your recipe through a lye calculator with any and all adjustments.
Additive Suspension: Both hot and cold process can provide a thick batter that allows for heavy additives to remain suspended in the soap. With cold process you will need a thick trace to suspend heavier objects. With hot process the batter is likely more than tick enough without any extra hand blending.
Do-overs: If you get a batch of cold or hot process soap you can rebatch it as a do-over. Rebatching can be done to add in a forgotten fragrance, enhance a muted scent from flash in the original process, super fat the batch, add in lye to a batch with too much free oil, add in oils to use up any free lye, and more.
This is truly as second chance soap.
Disadvantages Common to Hot Process and Cold Process Soap Making
Try as we might, we only found two real disadvantages shared by hot and cold process soap making. They both involved lye.
Handling Lye: Working with lye is the most talked about drawback of making soap from scratch. If you have never worked with lye it can be intimidating at first. Lye is a strong alkali base that can burn you when not handled properly. See Tips for Working with Lye at the bottom of this post.
Equipment Separation: Any items that come into contact with lye should not be reused for food. This applies to bowls, cups, utensils and even the Crock pot. For anyone that makes soap on a regular basis, this is no big deal. But for the first timer, trying it to see if they like it, it can be a pain. Nobody wants to lay out $20 for a Crock pot they might only use once.
Hot Process Advantages
Nearly Instant Gratification: The saponification process (turning oils and lye solution into soap) occurs during the soap’s cook cycle. This means that you can technically use the soap as soon as it has cooled and hardened. However, I like to give it at least one day to ensure all the lye is completely used up. It’s best to test the pH level before using any batch of soap. There are some pH tips right after the advantages and disadvantages of each process.
Super Fat Management: It is extremely easy to control the oils left for super fatting. You simply add the extra oil after the cooking and in-pot saponification is complete. Unlike in cold process, the lye has been nearly completed used up. This means your added oils will remain as unsaponified oils.
Natural Rustic Look: Hot process soap has a distinctive rustic look to it. This can go in either advantage or disadvantage column. In my experience this is an advantage because most people willing to spend $5 to $8 on a bar of handmade soap want authenticity. And let’s face it. Old fashioned “mountain” or “farm” soap is about as authentic as it gets. It’s even better because you can get the look of lard or tallow soap with coconut oil and similar animal free oils.
Clean-up: When the work is done all that is left in the pot is dried soap. This is the easiest clean up ever since you just add water.
Heat Source Options: You can use a slow cooker, such as Crockpot – or a double-boiler on the stove top. Using a slow cooker gives you flexibility in where you make your soap and how much you make at once. When I got my first big order for hot process I went to Walmart and bought three extra large slow cookers. Each could handle a double batch (5 lbs.). I was knocking out six batches (15 lbs.) per hour (time staggered and oils super-batched).
Lesson Learned
Things got scary a couple times. More than once I was stirring two pots at once during volcano eruptions. This is when the soap mushrooms up the sides of the container and overflow. That 220 F degree soap feels a lot like lava too if you let it hit you.
Volcanoes can erupt in two to three seconds; spewing boiling soap over the edge of the pots.
Even though I thought I timed everything well enough apart to avoid this situation, I should have given myself at least 15 minutes between starting each batch. I did that on the next round and had no emergencies.
Note: Saponification is the natural bio-chemical reaction of oils and lye solution reacting to create soap.
Hot Process Disadvantages
Constant Supervision: You always need to pay close attention when making hot process soap. Hot process soap expands several times its liquid volume size when you cook it. This means that if you want to make 2.5 pounds of soap your pot needs to be able to handle the volume of at least 7.5 pounds. And I would go even bigger, especially in height. The hot soap tends to mushroom for brief periods until stirred down.
Working with High Temperatures: During the cook cycle hot process soap will often reach temperatures greater than 220 F degrees. This is hotter than boiling. This is common when cooking stews and chili on Crockpots as well. But I wanted to mention it having brushed my wrist against the hot ceramic pot insert more than once.
Difficulty with Fresh Additives: It can be hard to add things like fresh milk into hot process soap due to the heat. It can be done. It just takes practice and patience to get it right.
Rustic Look: Again, I find the rustic look to be a benefit – especially for those discerning customers who crave authenticity. Some people, however, do not like it. To them it is a disadvantage.
Design Limitations: To make swirls and intricate patterns you need a thin trace batter. Cold process is ideal for this, but hot process is not so much. You can make sone layering effects with hot process, but these are not typically “smooth transitions”.
Fragrance Flashing: Essential oils and fragrances with low flashpoints can lose potency if the temperature of the soap is too high when the fragrance is added. This is something you can control easily enough with a thermometer, but it worth mentioning because it happens to first timers quite a bit.
Cold Process Advantages
Artistic Customizations: Cold process soap is ideal for using complex layering and swirling techniques. You can even slightly adjust the trace thickness of each element added to generate the exact look you want.
Texture: Another artistic consideration is texture. Although this is as much about feel as it is look. Once more, by using different consistencies of “trace” you can add ripples and smooth icing-like effects to each loaf.
Fresh Additives: Cold process is ideal for adding in fresh ingredients such as milk, yogurt, and purees. It is basically a matter of ‘set it and forget it’. These tend to be more difficult to manage in hot process.
Scents: Cold process soap goes through a much slower saponification process that generates far less heat. This means fragrances with a lower flash point (dissipation rate due to high temperature) work much better than on hoot process where the soap surpasses 220 F degrees.
Cold Process Disadvantages
Cure Time: The most talked about disadvantage with clod process is the amount of time it takes bars to cure. All that fluidity that makes it so nice for layering and swirling also means it takes 4 to 6 weeks for that added water to evaporate out and form a hard, long-lasting soap bar.
Colors: Some colors tend to run or not stay as vibrant with cold process soap making. This is due to the high pH level in the yet unsaponified soap batter. While oils have neutral or low pH levels, lye solution tips the pH scale at 13 to 14.
Fragrances: Fragrances and essential oils with a flashpoint below 180 degrees Fahrenheit should be used with caution. This is because they can fade quickly as the heat increases. The gel phase of the cold process typically reaches 180 degrees Fahrenheit.
Saponification Time: The saponification typically takes 24 to 48 hours in cold process soap depending on multiple factors. If you are already aware that you will wait 4 to 6 weeks for the soap to fully harden – the extra day or two to fully saponify is not a big deal.
However, some soapers try to use a water discount in their lye solution to speed up the curing time. This can work if you know what you are doing – BUT it does not speed up saponification time.
If you do a water discount in cold process to reduce curing time, you must still give it at least 24 hours to fully saponify (turn to soap). Then you should absolutely test the pH to ensure it is safe to use. You are looking for a level between 7 and 10, with 8 to 9 being considered ideal for most people.
Understanding pH Levels
Now that you know what process you want to use, remember to do a pH test to ensure the soap falls between 7 and 10 before you use it. A rating of 8 to 9.5 is common. The lower the pH value, the less alkali the bar will be a pH (a rating of 7 is neutral).
A pH level above 10 can cause skin irritation and a burning feeling. Try to stay below a pH of 9.5.
The pH can best tested with litmus type paper strips or plastic strips as well as meters.
An easy way to compare the alkali strength by number of to compare it to food of each pH rating. Here are some common ingestible items for comparison:
- pH 6: Milk & Coconut (slightly on the acidic side)
- pH 7: Distilled Water (neutral)
- pH 8: Corn & Banana (slightly on the alkali side)
- pH 9: Avocado & Celery (more on the alkali side)
- pH 10: Broccoli & Radish (even more of an alkali)
Tips for Working with Lye
While I am not afraid of working with lye, I do have a healthy respect for it. In my opinion, everyone who uses lye should respect it and take every precaution to ensure their safety and that of anyone or anything around them.
Here are some of the tips I have found most helpful over the years:
- Always use safety gear when working with lye. At minimum this should include full length sleeves, leg and body protection, and good safety goggles that will protect form the sides, top and bottom – as well as front.
- Keep your lye in a safe dry place free from children, animals, and any others that might get into it. This goes for long-term storage as well as during and after weighing and prior to/during use.
- Always measure your lye separately and away from the proximity of any liquids. Lye sucks any moisture it can find right out of the air and will start clumping if not kept completely dry. I measure mine in a small plastic container with a screw on lid. I weigh out exactly what I need then screw the lid on and put the lye aside.
- Weigh your lye in grams to get the most accurate measurement when using a typical digital scale. Most kitchen scales are only accurate to one decimal point. One tenth of one ounce is the same as 2.83 grams. Simply by measuring in grams you are getting nearly three times the accuracy.
- Do not use aluminum utensils or pitchers/bowls with lye. They have a strong reaction when combined. Stick with stainless steel, thick heat resistant glass and heat resistant plastics.
- Always add your lye to the water – NEVER the other way around. When lye meets water, an exothermic reaction occurs. The combined liquid is a “lye solution” that reaches near boiling in seconds. By pouring the lye into the water slowly, and stirring it in to help dissolve it gradually, you have the most influence over the process.
- Slowly pour the lye solution through a small particle stainless steel mesh strainer when adding it to the oils. This will help catch any undissolved lye crystals before they get into your oils and cause unsaponified hot spots in the soap. I bought mine at the dollar store a year ago and it still works great.
>>> Get the Inside Advantage
Now that you know what process you want to use, it’s time to look at the tools you will need to make your soap.
You can do this without even leaving this website. Click here to explore 11 Things Every Soap Maker Needs to Know.
Or you can just download the spreadsheet that lists the tools needed for each process type if you are in a hurry. It is below.
There is a “Cost” column to the far right of the download version so you can price out your equipment as you go.
I would take a few minutes to check out the post to get more insights when you have time though. It can save you a lot of time and money in wasted trial in error.
Happy Soaping!