Liquid Castile Soap

Liquid castile soap is the foundation of sustainable, versatile soap making. Unlike cold-process soap that creates bars, this hot-process liquid soap recipe uses pure olive oil to create a concentrated base that can be diluted into hand soap, body wash, shampoo, cleaning products, and countless other applications. The true castile tradition uses only olive oil, but slight variations can create specialty versions. This advanced recipe teaches the hot-process method where lye and oils are actively heated to accelerate saponification, creating soap ready for immediate dilution within hours rather than weeks of curing. Master this technique and you unlock unlimited possibilities for soap product creation.

Ingredients

Oils & Butters (total: 32 oz / 907g)

• 32 oz (907g) Olive Oil (100% - pure castile recipe)

Lye Solution

• 4.4 oz (125g) Sodium Hydroxide (NaOH)
• 10 oz (283g) Distilled Water

Optional Additives (after saponification)

• Essential oils for scent (0.5-1 oz per 32 oz finished soap)
• Salt for adjustment (if needed)
• Distilled water for dilution

Equipment Needed

• Large stainless steel pot with lid (5+ quart capacity)
• Candy/deep-fry thermometer (preferably 0-300°F)
• Wooden spoon for stirring (dedicated to soap making)
• Heat source: stovetop or slow cooker on low setting
• Digital scale accurate to 0.1 oz
• Stainless steel or glass bowls for lye preparation
• Measuring cups and spoons
• Glass jars for storage and dilution
• Safety equipment: goggles, nitrile gloves, apron, long sleeves
• pH testing strips (optional but recommended)
• Vinegar (5% acidity) for safety backup
• Protective covering for workspace
• Water source for dilution

Instructions

Step 1: Safety Setup and Workspace

Cover your work surface with newspaper or protective material. Arrange all equipment and ingredients within easy reach. This process involves active heating and monitoring - ensure nothing will distract you. Put on all safety equipment including goggles, gloves, and apron before beginning. Open windows for ventilation. Have vinegar nearby as a lye safety backup. Liquid soap making requires more active involvement than cold-process soap making.

Step 2: Measure and Prepare Oils

Weigh your olive oil precisely on your digital scale - you need exactly 32 oz. Place the olive oil in your large stainless steel pot. This will be your primary workspace for the hot-process method. Have your thermometer ready to monitor temperature throughout the process. Olive oil is your entire oil base, so ensure quality oil from a reputable source.

Step 3: Prepare Lye Solution

Wearing goggles and gloves, carefully add lye to distilled water in a heat-safe glass or stainless steel bowl while stirring slowly and deliberately. Always add lye to water, never water to lye. Stir constantly - the reaction is exothermic and will heat to 150-200°F (65-93°C). Continue stirring for 1-2 minutes until the lye completely dissolves. The solution should become clear.

Step 4: Gentle Heat to Combine

Place your pot of olive oil on low heat - you're not trying to cook the oil, just warm it gently to reduce temperature shock when lye is added. Warm the oil to approximately 125-130°F (52-54°C). Monitor closely with your thermometer. Once the lye solution has cooled to approximately 125-130°F (52-54°C) as well, you're ready for combining. Both components should be similar temperatures.

Step 5: Combine Oil and Lye

Once both are warmed to similar temperatures, carefully pour the lye solution into your olive oil while stirring constantly with your wooden spoon. Pour slowly - this is an exothermic reaction and will generate heat. Stir thoroughly and constantly for 5-10 minutes. The mixture will begin to thicken and lighten in color. Continue stirring until you achieve trace - the pudding-like consistency where soap drips briefly remain visible.

Step 6: Begin Hot Processing

Once trace is achieved, increase heat to medium and continue stirring frequently - not constantly, but every 2-3 minutes. The mixture will heat to approximately 180-200°F (82-93°C) during this process. This heating phase accelerates saponification. Maintain temperature in the 170-190°F (76-87°C) range. The soap will continue thickening. Stir thoroughly whenever you check temperature to ensure even heating.

Step 7: Monitor Saponification Progress

The soap will progress through several visible stages. First, it becomes thick and custard-like (this happens quickly). Continue heating and stirring. After 20-30 minutes, the soap may look like a thick, tan, cottage-cheese consistency. This is called "phase separation" and is normal during hot-process. Don't panic - the mixture will come back together as saponification continues.

Step 8: Continue Heating Through Phase Separation

Keep the temperature in the 170-190°F (76-87°C) range and continue stirring every 2-3 minutes. The "separated" appearance will persist for 30-60 minutes. This is the saponification process working actively. The mixture will eventually become more uniform again as lye is completely consumed and proper soap forms. This is the hallmark of hot-process - you can watch saponification happen.

Step 9: Test for Gel Phase Completion

After 45-90 minutes of heating, the soap should appear more uniform and glossy. Test for completion by performing the zap test: carefully place a small amount of soap on your clean, dry finger and briefly touch it to your tongue (very briefly). If it zaps your tongue with electricity, lye remains and the batch isn't ready. If there's no zap, saponification is complete. Alternatively, use pH testing strips - finished soap should read pH 9-10.

Step 10: Slow Down Heat

Once saponification is complete and the zap test is negative, reduce heat to the lowest setting or turn the burner off if using a slow cooker. The soap is now saponified but concentrated. Allow it to cool slightly - it doesn't need to be scalding hot, just warm enough to be pourable. This is a good time to add any essential oils or fragrances if desired.

Step 11: Optional Essential Oil Addition

If adding essential oils or fragrance, wait until the soap has cooled to approximately 160-170°F (71-76°C) to prevent volatile oils from evaporating. Add 0.5-1 oz of essential oil per 32 oz of finished liquid soap. Stir thoroughly to ensure even distribution. Scent is optional - plain castile soap is equally versatile and can be scented during dilution for specific applications.

Step 12: Prepare for Dilution

Your liquid soap is now complete but extremely concentrated - not suitable for direct use. Most concentrated castile soap is diluted 1:1 or 1:3 with water (or even higher dilution) before use depending on the application. Have your glass jars ready. You can store the concentrate as-is or begin dilution immediately. The concentrate will keep indefinitely if stored in an airtight container.

Step 13: Basic Dilution for Hand Soap

For hand soap, a simple 1:1 dilution often works well. In a glass jar, combine equal parts concentrated liquid soap and distilled water. Stir thoroughly to combine. The resulting mixture should be a clear, thin liquid. If too thin, add more concentrate; if too thick, add more water. Allow the mixture to sit for 24 hours - it will become clearer and more uniform.

Step 14: Adjust Consistency with Salt

If your diluted soap seems too runny, add salt (sodium chloride) in small increments. Add 1/2 teaspoon of salt, stir thoroughly, and observe. Salt causes the soap to thicken slightly. Add salt sparingly - a little goes a long way. Stir for several minutes after each addition to allow the salt to fully interact with the soap structure.

Step 15: Storage and Uses

Store concentrated castile soap in glass jars away from direct sunlight. It will keep indefinitely. Diluted versions should be stored similarly but may have shorter shelf life - 6-12 months is typical depending on water purity and contamination prevention. Label all jars clearly with contents and dilution ratio. Castile soap can be diluted differently for different applications - 1:1 for hand soap, 1:3 for body wash, 1:10 for cleaning products.

Step 16: Testing and Adjusting

Once your diluted soap has rested for 24 hours, test it by washing your hands or a small area of skin. The feel should be clean and not slippery. If it's too drying, add a small amount of glycerin (about 1 tablespoon per 32 oz of diluted soap) for moisturizing. If it's too slippery or feels filmy, the soap is likely over-diluted and needs more concentrate.

Step 17: Multiple Dilutions

Create multiple diluted versions for different purposes from one batch of concentrated soap. Keep the concentrate, then dilute smaller amounts for: hand soap (1:1), body wash (1:2), shampoo (1:3 with added conditioning oils), and cleaning products (1:10). Label each clearly. This versatility is the power of castile soap making.

Tips for Success

• Heat management is critical: Keep temperature in the 170-190°F (76-87°C) range. Too hot and you risk ruining the soap or creating safety hazards. Too cool and saponification slows dramatically.
• The zap test is your best friend: This simple test (brief tongue touch) tells you exactly when saponification is complete. Learning to trust this test is essential for hot-process soap making.
• Phase separation is normal: Don't panic when the soap looks separated and curdled. This is exactly what should happen during hot-process. It will eventually come back together as saponification completes.
• Concentrated soap is powerful: A little concentrated castile soap goes a long way. Always start with less concentrate and add water, rather than starting dilute and trying to add concentrate.
• Water quality matters: Use distilled water for dilution. Tap water containing minerals can create cloudiness in your finished liquid soap.
• Glycerin addition: The hot-process method consumes glycerin (which forms as a byproduct in soap making), so your finished liquid soap will be less moisturizing than cold-process soap. Adding glycerin (1-2%) restores moisturization if desired.

Variations

• Coconut Castile: Substitute 30% of olive oil with coconut oil for creamier lather and harder soap. Adjust lye amount to 4.6 oz for 32 oz of oil blend.
• Herbal Infusion: Steep dried herbs (chamomile, calendula, lavender) in your olive oil for 2-4 weeks before making soap for herbally-infused castile soap.
• Super-Saponified Castile: Increase lye amount to 4.8 oz to create "super-fatted" castile soap that's more moisturizing than the standard version. This leaves unsaponified oils that condition skin.

Cost Breakdown

Total Cost (concentrated): $6.25Total Cost (32 oz diluted 1:1): $10.30Estimated Cost per oz (diluted): $0.32

Related Recipes

• Hemp Seed Oil Soap Recipe - Cold-process conditioning alternative
• Honey Oatmeal Palm-Free Soap Recipe - Bar soap alternative
• Sea Salt Spa Soap Recipe - Another specialty option

Advanced Technique Note: Liquid castile soap hot-process method teaches fundamental saponification principles that apply to all soap making. Mastering this technique builds confidence and understanding that translates to improving all your soap crafting abilities. The versatility of finished castile soap makes this technique valuable for creating a complete product line from a single batch.

Troubleshooting Liquid Soap

Soap Won't Thicken During Cooking

Ensure you're maintaining temperature in the 170-190°F (76-87°C) range. Too cool and saponification slows dramatically. Use a reliable thermometer - quick-read thermometers sometimes provide inaccurate readings. Stir frequently to ensure even heating.

Over-Heating or Burning

If soap develops a dark appearance or unpleasant smell, the temperature got too high or it cooked too long. Lower heat immediately and continue the process more gently. The soap may still be salvageable, though quality may be reduced.

Zap Test Still Shows Lye

This means saponification isn't complete. Continue heating, stirring every 2-3 minutes. The zap will eventually disappear as saponification completes. If after 3 hours of heating the zap test still shows lye, you may have made a lye-heavy recipe - proportions may be off.

Advanced Liquid Soap Techniques

Super-Fatting: Add 1-2 oz of additional oils after saponification is complete. These oils won't saponify in traditional soap making but will add conditioning benefits to liquid soap. Add glycerin or sweet almond oil for maximum conditioning.

Fragrance Timing: Add fragrance oils after the soap cools to below 160°F to prevent volatile compounds from evaporating. Essential oils can be added slightly hotter (around 170°F) since they're more heat-stable.

Water Amounts: You can vary final dilution dramatically based on application. Start with 1:1 for hand soap, but dilute up to 1:10 for cleaning products. Thinner soap goes further in commercial applications.

Product Line Development

One batch of liquid castile concentrate can create multiple finished products:

• Hand Soap - creamy, moisturizing (1:1 dilution)
• Body Wash - luxurious shower experience (1:2 to 1:3 dilution)
• Shampoo - with added conditioning oils (1:3 to 1:5 dilution)
• Face Wash - gentle cleansing (1:5 to 1:8 dilution with gentle additives)
• Floor/General Cleaner - powerful degreaser (1:10 to 1:20 dilution)
• Laundry Additive - sustainable washing (concentrate at 2-3 oz per load)

This versatility means one batch produces a complete product line, significantly increasing value and revenue potential from single production batch.

Advanced Technique Note: Liquid castile soap hot-process method teaches fundamental saponification principles that apply to all soap making. Mastering this technique builds confidence and understanding that translates to improving all your soap crafting abilities. The versatility of finished castile soap makes this technique valuable for creating a complete product line from a single batch.

Application Examples:

• Hand Soap: 1 part concentrate to 1 part water (creamy, moisturizing hand cleanser)
• Body Wash: 1 part concentrate to 2-3 parts water (luxurious shower experience)
• Shampoo: 1 part concentrate to 3-5 parts water (gentle hair cleansing with added conditioning oils)
• Floor Cleaner: 1 part concentrate to 10 parts water (natural, safe floor degreaser)
• Laundry Soap: 2-3 oz concentrate per load (sustainable laundry alternative)

Advanced Chemistry: Hot Process Saponification

Hot-process soap making accelerates saponification through active heating, compressing the process from weeks to hours. The exothermic reaction between lye and oils generates heat, which you maintain through external heating sources. This sustained heat accelerates molecular movement, allowing lye and oil molecules to meet and react more frequently.

During hot-process, you can literally watch saponification progress through visible stages. The "phase separation" that occurs midway (where soap appears curdled) is a normal intermediate step where the soap is partially saponified. Continued heating completes the process, transforming the separated appearance into uniform, glossy, saponified soap.

The advantage of hot-process for castile soap is speed - you can use the soap immediately after cooling rather than waiting weeks. The disadvantage is that heat-sensitive compounds in oils are partially degraded, and glycerin (which forms as a byproduct) is not retained in the finished soap. The final product is less moisturizing than cold-process but ready for use immediately.

Concentrate Economics and Scaling

Creating concentrated liquid soap base allows incredible scaling potential. A single batch of concentrate produces multiple finished products. This means:

• Lower ingredient costs per finished product through bulk purchasing
• Flexibility to create multiple product types from single production batch
• Ability to customize scent, consistency, and properties during dilution
• Significant profit margin improvement through value-addition during dilution

A $6.25 concentrate batch can produce $30-50+ in finished soap products through various formulations and presentations. This economic model is why liquid castile base is used commercially by soap companies worldwide.

Troubleshooting Advanced Problems

If your soap has white precipitate floating in it, you likely have lye that wasn't completely incorporated. Using the zap test will confirm - zap means lye remains. Continue heating until the zap test is negative and the precipitate dissolves.

If soap develops a gritty texture, you either have undissolved salt crystallizing or soap that partially resinified (hardened). Gritty texture is mostly cosmetic - the soap still functions, though appearance and feel are compromised.

If soap smells rancid or off, oils may have been oxidized before use. Source fresh oils and verify their age. Store oils in cool, dark places to maximize shelf life.

Commercial Applications

Large-scale soap makers produce liquid castile concentrate specifically to create multiple product lines. This efficiency explains why liquid castile is the foundation of many commercial soap lines. If you're interested in growing a soap business, mastering liquid castile production is essential for scaling profitably.

The concentrate's long shelf life means you can produce in batches during cool months (avoiding heat issues with base oils) and create diluted finished products throughout the year, spreading labor more evenly and avoiding seasonal supply chain issues.

• Multi-Purpose Cleaner: 1 part concentrate to 8-12 parts water (all-purpose household cleaner)