15-Minute Castile Soap HTHP Experiment (No crockpot necessary)

Updated: Sep 11, 2019


The Ultimate Guide to Hot Process Soap- Quick Cure Castile Soap


For me, soap making is not only a fun and exciting art form, but also a never-ending science experiment and quest to further my knowledge and understanding of the saponification process. In my book, The Ultimate Guide to Hot Process Soap, I teach readers how to make informed High Temperature Hot Process (HTHP) recipes, mostly with the goal of providing an education on how to use physical science and chemistry to create fluid hot process recipes. I also provide suggestions and recommendations on how to formulate HTHP and HTFHP (high temperature fluid hot process) recipes, with a strong recommendation for using recipes high in saturated fats.


Recipes that are high in unsaturated fats have a much lower rate of reaction for the formation of an emulsion (trace) and saponification compared to those that are higher in saturated fats. When creating HTHP, the goal is to quickly and efficiently increase the rate of saponification through high temperatures, increased molecular contact through mechanical mixing and through use of informed recipes that promote these goals. Using recipes that do not support these objectives hinders the process. It decreases the reaction rates, increases the risk of drying, increases the rate of heat dispersion, may cause problems with your immersion blender, and may require excessive mixing (which can be annoying and sometimes physically not feasible by all soapmakers)… and these are just to name a few! All of these things negatively affect the recipe’s fluidity which is often the goal when making soap using the HTHP method.


Although these are all common complications of uninformed recipes, if your main objective is not fluidity, and you have a good immersion blender and don’t mind a little mixing, in addition to a little bit longer of a process, HTHP can still be used to quickly and efficiently create soap from recipes that are high in unsaturated fats or not created specifically for the intended purpose of HTHP.


Today we will perform a 15 minute castile soap experiment made from 100% olive oil using the HTHP method. The recipe will be made with a 28% water concentration based on the total oil weight and will be made without a crockpot, although you may use one if you prefer. This recipe is designed with a water discount to increase the reaction rate and will result


a thick viscosity and a rustic appearance. If you would prefer a more fluid recipe, use the full 38% but expect a slightly longer reaction time. We will also use a few drops of clove oil which contains eugenol which will help accelerate the overall rate of reaction. Eugenol is also found in cinnamon oil or you can use stearic acid or finished soap as a trace accelerant. When any of these trace accelerant options are added in small amounts, there is no significant or noticeable change in fragrance and the small amount will not cause skin irritation because the additives are immediately broken down by the lye.


Eugenol is an alcohol that has an acidic proton. It is considered a phenolic compound and reacts immediately with alkalines. We can add eugenol to recipes that are high in unsaturated fats, like our castile recipe, and it will immediately react with the sodium hydroxide and increase the overall reaction rate. When we add this component to the increased mechanical mixing and increased temperatures from the HTHP method, in addition to a reduction in water, we are quickly able to accelerate the rate of reaction and create a lovely castile hot process soap in just a few short minutes.



Is the BEST way to make castile hot soap? It really all depends on your personal preference, but this is A way to make castile hot process soap and is a fun experiment that shows the importance of using an informed recipe when making HTHP soap. Some people may see this as “extra work” when it can be done over an extended period of time in a crockpot or made with CP. Others, like me, will see it as a fun and exciting challenge and a super fast, easy and efficient way to make quick- and extra hard castile soap- sans crockpot.


The benefits of this method with this castile recipe:

-The total amount of time required for saponification is less than 15 minutes (compared to 60-90 minutes in LTHP and 48-72 hours in CP)

-From start to finish, including prep, the soaping process and cleaned and dried dishes, it will take you less than 25 minutes total to make this recipe

-Your soap can be cut and unmolded an hour after you make it (compared to up to two weeks in CP soap)

-You can use your castile soap the same day you make it

-It creates a very gentle and bubbly bar, even on day one

-The water discount yields hard initial bars and significantly decreases the amount of time needed for water evaporation

-The boiling point of water is 100C and boiled soaps decrease in water concentration more quickly compared to those that do not (CP and LTHP)

-You don’t need a crockpot or tons of space

-You can make the 12 bar recipe for less than $5.00 ($0.14/oz olive oil from Walmart and just a few ounces of lye)


Customize it!

If you want to personalize or update the recipe, you absolutely can. If you want a more fluid recipe, you can cook with with more water or use a water discount and then add the moisture to the recipe after it has cooked. A great option for adding moisture back after the cook is to add the rest of your moisture concentration to the end in the form of milk or yogurt. Yogurt and milk will add fluidity, add lather from the sugar, neutralize any remaining NaOH and more. If you increase the water concentration at the beginning of the recipe, it will increase the length of time required for saponification and will take longer, so this is something to consider and may affect your recipe. It may also lower the temperature of your recipe if adding cooler ingredients so you may need to re-add a heat source. These are a few options for increased fludity, but you can also add fragrance, herbs, additives, colorants…. whatever you want to make it your own!


This experiment makes plain ole fashion, quick-hardening castile soap, but please feel free to customize it however you would like! I make this soap for at home use so I could care less if it was pretty or ugly, as long as its gentle and moisturizing, but adapt the recipe however you see fit for your needs.


Recipe: -32oz olive oil (6% cook superfat) -8.96 ounces water (This is a 28% water concentration and is a very high discount for hot process soap. It will result in a very thick soap at a faster rate. For a more hydrated soap, use 32% or 10.24 ounces or the full 38% at 12.16) - 4.07 ounces NaOH -Few drops of clove (1.5-2.5ppt for an exact measurement, but I usually just sprinkle a few drops) You can also use finished castile soap or add stearic acid for a trace accelerant if you don’t have clove oil (be sure to calculate stearic acid in soap calculator)


Experiment Directions: Use the knowledge and directions from The Ultimate Guide to Hot Process Soap for the HTHP method (continuous immersion blender high temperature hot process)


1. Because the recipe as a decreased rate of reaction, you can use a higher starting temperature. I heat my oils to 230F (do not exceed 250F)


2. Complete the HTHP continuous mixing process until the soap has finished with the heat expansions and then cover with plastic wrap


3. Stir every few minutes until the pH has reached 8.0-10.0. (This is the perfect time to do your dishes!)


4. Mold your recipe, you may refrigerate or freeze if desired. Be sure to check your recipe every 10 minutes. As soon as it has hardened enough to cut, please be sure to do so. If you wait too long, it may be too hard and may cut unevenly (or not at all)


5. Cut and enjoy a small sample the same day. Be sure to cure the rest for longer lasting, harder and better lathering bars!

(See chapter 17 for more information regarding curing in hot process soap)


Video (Posted in Members Videos) I left the camera on the entire time when shooting this so that you could see exactly how the process works and how long to let it sit, which can be shorter or longer depending on your personalizations, in addition to checking the temperature and the pH of the soap. Checking the pH is not necessary if you are familiar with and comfortable with hot process, but may be necessary for beginners or pH sensitive ingredients. The pH will also continue to decrease over time, in part due to the acidic nature of carbon dioxide


Please disregard all of the extra noises, that is me cleaning up all of the dishes and putting stuff away from the morning’s batches. I was all done by the time the castile soap was done and was ready to run out the door! I will be tracking the cure time of this soap and sharing it with you guys too!


Happy Soaping!