Soap is essentially a chemical reaction that occurs between a strong alkali and a fatty acid. The strong alkali is sodium hydroxide, commonly known as lye. The fatty acid can be various oils or fats.
This reaction is called saponification and occurs from the point of mixing to the time it takes for the soap to fully cure. Glycerol is also produced, which is a moisturising by-product of the saponification. The glycerol can be removed for smooth products like lotions.
You can make soap in 3 main ways: melt and pour, cold process and hot process.
The advantages and disadvantages of each method
1) Melt and pour
Pros: Super simple. You melt premade glycerin soap, add whatever colours and scents, and pour into molds.
Cons: More expensive, less rewarding, less customizable.
2) Cold process
Pros: Less steps than hot process and a smoother and lighter end product.
Cons: Use of dangerous lye, must cure soap for weeks for it to harden.
- The work area should be well ventilated, or better yet outdoors.
- Slowly pour lye from small cup into bowl with water, somewhere safe like in a sink (never reverse the order of pouring). A chemical reaction will occur, producing heat. Put aside and allow to cool to around 35-40C. This will likely take 1-2 hours.
- Melt your fat(s) in a separate container, which you should heat to around 35-40C. You can use the double boiler method to heat the oils. Basically you have one larger pot with water that you heat and a smaller pot with the oil that fits in the hot water. If you need to cool your oils quickly, you can just replace the hot water with cold water. Make sure you use pots that are tolerant to these changes in heat.
- When they’re both in the 35-40C range, slowly mix the lye-water mixture into the fat (never the reverse). If the temperatures aren’t the same, the oil should be slightly warmer than the lye-mixture. First stir manually for a couple of minutes with the stick blender. Then switch on the stick blender until “trace.” Avoid adding air bubbles while you mix by keeping the hand blender below the surface. Blend for 3 minutes, stir for 2 minutes. On and off until trace.
- The “trace” or “ribbon” phase refers to the emulsification of the oils and lye-water. If you can trace a ribbon of the mixture across the top of the mixture and the ribbon doesn’t immediately meld then the mixture is emulsified. Alternatively, you can trace a path through the mixture and it will take time to even out again.
- After trace is achieved, add adjuncts (for colour, scent and exfoliation) and mix.
- Pour the mixture into a wax parchment-lined mold.
- Lightly hit the mold on a hard surface to remove bubbles.
- The soap will “saponify” over the course of 48 hours, whereby the lye will react with the fat to form soap.
- Insulate the mold to maintain the heat necessary for saponification in the first 24 hours. The soap starts off by going translucent before going solid.
- If the soap is cracking, removing insulation. Regardless, remove insulation after 48 hours.
- Carefully remove the caustic soap and cut the soap into bars.
- Allow the bars to cure for a month to harden. You either have to turn the bars daily or, if you build a rack with a breathable screen, you can turn them weekly.
- The curing allows the bar to harden by moisture evaporation and the lye neutralizes.
3) Hot process
Pros: Shortened the soap curing process, useable once cooled, results in a rustic look.
Cons: Use of dangerous lye, more steps and greater attention, rougher than the post-curing cold process soap.
The only difference from the cold process is that instead of pouring the trace mixture into a mold, the mixture should be set on low in a slow cooker for 1 hour, stirring every 15 minutes.
Ready to use after solidifying in the mold for 24 hours but for a longer lasting bar, the hot process soap still benefits from a few weeks of cure time.
Equipment and supplies
- Metal kitchen thermometer
- 2 melt-resistant plastic, heat-resistant glass or stainless steel container (4 – 6 quarts) for:
- Mixing lye into water
- Melting fats and mixing in the lye-water (like a cooking pot)
- Glass or plastic measuring cup to hold the lye
- Heat-resistant plastic or disposable wooden spoon for mixing
- Digital scale
- Stick blender (the most efficient way to blend the lye-water-fat mixture)
- Safety goggles
- Rubber gloves
- Long sleeves and pants
- Heat-resistant mold (I made wooden molds)
- Sharp object for cutting soap into bars
- Lye (100% sodium hydroxide)
- Various combinations of fats (ratios depend on the recipe, different fats will produce different lathers, textures and colours)
- Oils like olive, canola, coconut, deer tallow and shea butter
- Lard (pig fat) makes a hard, white bar with a creamy lather. Moisturizing
- Vegetable oils will be off-white and softer than animal fats
- Palm oil is a vegan alternative for tallow and makes a hard soap. The lather is creamy, but the low amount of glycerin means it’s not very moisturizing
- Suet (beef fat) will be a hard, brown bar with a creamy lather. Moisturizing
- Coconut oil will give a bubbly lather and a hard, white, dry bar
- Olive oil is moisturizing, give a creamy lather (soft, small, smooth bubbles), and tends to be light yellow or green. Castille soap is 100% olive oil. Pomace olive oil is an affordable alternative to pure olive oil. The pomace oil is made from the last press of olives, which includes less oil and more other parts of the olive. The solids in pomace oil will lead to a faster trace and a darker soap. High olive soaps take longer to cure (and begin off soft), but once fully cured will become hard yet soft.
- Goat milk is moisturizing.
- Castor Oil has lots of lather but the trade off is stickiness, so you need to keep the ratio under 10%
- Shea Butter: Since not all the shea butter can be saponified, the remaining gives greater moisturization and gentleness.
- Cocoa butter: hard, but smooth.
- Soap Additives:
- Colorants: teas, spirulina, beet juice, red cabbage water, black walnut hull
- Fragrances: essential oils are pure extractions that are expensive and subtle, artificial fragrances will give you a much stronger sent. Essential oils should be used at a rate of 2-5% of the weight of your fats.
- Exfoliates (coarseness and quantity depends on the type of soap bar: oatmeal, dried herbs, coffee grinds, seeds, flower petals, orange peel
Creating your own recipes
- Different fats need different quantities of lye for saponification. A lye calculator is essential. Use a lye calculator to establish ratios: http://www.soapcalc.net/calc/SoapCalcWP.asp
- Alternatively, you can use a Saponification Chart
- The same recipe will require different proportions of ingredients depending on the method (cold or hot).
- You want to add slightly more fat than will be converted into soap by reacting with lye. You want a balance of about 5% excess fat to ensure a moisturising benefit from the fat. Too little fat and your soap will be harsh and dry. Too much fat and the soap will spoil.
- You can replace water with teas, which will provide subtle colours and scents.
- Use an oil chart to gauge how much of any particular oil you should use in a recipe.
My own process
I like the hot process because the heat keeps the soap melted even once its gone to trace (giving me more time to transfer to the molds), I like the rough look of the soap, and there’s a shorter cure time by cooking out the lye.
Here’s a very short summary of the hot process:
1) Melt oils in the slow cooker.
2) Add lye to water in a measuring cup (ml = grams for water)
3) Add lye-water to slow cooker fats.
4) Cook on low for 2 hours.
5) Add adjuncts at the end.
6) Cure for 24 hours.
7) Cut bars.
- Liquid sinks while fat floats: the mixture was the wrong temperature. The solution is to heat to the right temperature and mix.
- Streaks in the soap: melt, remix and harden.
- Cracks in the soap: stirred excessively, too much lye, got wet and re-dried, or dried too fast.
- Greasy soap has too much fat.
- White deposits: too much lye or hard water.
- If the soap is rising excessively at the centre or liquid is separating on top, the mixture is too hot and you should uncover the mold for 12 hours.
- If your soap ends up with a patchy colour or as translucent, the soap was too cold while settling.
Notes and warnings
- The biggest issue when making soap is the danger of using lye, which can cause serious burns. Always take the necessary precautions like wearing safety glasses, rubber gloves, long-sleeved clothes and a face mask. Before the soap saponifies, the soap is still caustic. Keep small animals and children far away from the soap-making area.
- Use dedicated equipment for soapmaking to avoid cross contamination with food. Use cardboard or many layers of newspaper on your work area.
- You have to mix lye to your liquid. Do not add the liquid to lye or you’ll get a rapid and dangerous expansion of caustic liquid.
- Avoid sprinkling lye into hot water because if the mixture gets too hot it may overflow.
- The difference between stick blending and hand stirring will be 2-20 minutes versus 20-60 minutes. Trace occurs at different times depending on the ingredients.
- Reaching trace will occur at different times depending on the ingredient composition of the mixture. The fat and lye need to be precisely measured but the liquid doesn’t since it only effects how quickly the soap sets to trace. You may want the trace phase to be slower to add adjuncts (colour, scents, beeswax etc).
- An ash may form on the dried soap, which can be scraped off if so desired.
- The longer the curing process, the harder the bars will become and longer they will last in use.
- If you’re making your own fats, remove as much meat from the fat as possible, boil the fats (adding 2 tablespoon of salt per 1kg of fat) and leave in the fridge overnight for the pure fat to separate and float to the top.
- You can ensure a correct pH balance by using testing strips to ensure the soap is around 7-10 on the scale. You can rebatch the soap and add more fat if the pH is above 10 after a month of curing.
The old method of making soap involved deriving lye from potash. Many Canadians know potash as something mined in Saskatchewan for export to fertilize the farms of the world. Original potash, preindustry, was literal ash put in a pot and mixed with water to form lye. When settlers first came to Canada from Europe, they brought knowledge of soapmaking. The settlers would have to clear the land for farming. The trees and brush would be burned in large fires. The ash was collected and mixed with rendered fat from farm animals to make soap. Soap was one of the key barter items in colonial Canada.