How to Make Cold Process Liquid Soap

Complete Guide to Making Soap Paste and Diluting to Liquid Soap

Liquid soap making uses potassium hydroxide (KOH) instead of sodium hydroxide (NaOH) to create a soap that remains liquid rather than solid. This guide covers the paste method of cold process liquid soap - making a concentrated soap paste that you dilute into liquid soap.

Understanding Liquid Soap vs. Bar Soap

Bar Soap (NaOH)	Liquid Soap (KOH)
Sodium hydroxide (NaOH)	Potassium hydroxide (KOH)
Hard bars	Liquid/paste
Lower superfat (3-8%)	Lower superfat (0-3%)
4-6 week cure	Dilute immediately or after paste cure
Direct use after cure	Requires dilution

Why make liquid soap?

Create custom hand soaps and body washes
Control ingredients and avoid harsh detergents
More economical than buying bottles
Customize scent and properties
Natural alternative to commercial options

Safety First

KOH is more caustic than NaOH - extra care is essential!

Safety equipment (MANDATORY):

Safety goggles or face shield
Heavy-duty rubber gloves (not latex - KOH can penetrate)
Long sleeves and long pants
Closed-toe shoes
Well-ventilated area
Vinegar nearby for spills

Safety rules:

Always add KOH to water, NEVER water to KOH
Work in well-ventilated space (KOH fumes are strong)
Keep pets and children away
Never touch raw soap paste
KOH heats water even more than NaOH does

Equipment You'll Need

For making paste:

Heat-safe containers - ONLY use stainless steel, silicone, or plastic #5 (PP) or #2 (HDPE)

NEVER use aluminum - KOH reacts violently with aluminum
Avoid glass - extreme heat can shatter it

Digital scale accurate to 0.1g
Slow cooker (optional but recommended)
Stick blender (immersion blender)
Thermometer
Silicone spatulas

For dilution:

Large pot or container
Heat source or patience (can dilute cold or hot)
Strainer or cheesecloth (for clarity)
Storage bottles (pump or squeeze)

Understanding Liquid Soap Formulation

Recommended Oils for Liquid Soap

Best oils (create clear, stable soap):

Coconut Oil: 25-60% (cleansing, lather, clear)
Castor Oil: 10-30% (lather booster, clarity, conditioning)
Sunflower Oil: 10-30% (conditioning, light)
Safflower Oil: 10-30% (conditioning, light)
Hemp Oil: 10-20% (conditioning)

Oils to use sparingly (can cloud soap):

Olive Oil: 10-30% max (tends to cloud)
Palm Oil: 10-20% max (can cloud)
Shea Butter: 5-15% max (can cloud)

Oils to avoid:

Solid fats like tallow, lard (will solidify when diluted)
Beeswax (won't saponify)
Mineral oil (won't saponify)

Superfat for Liquid Soap

Use 0-3% superfat maximum for liquid soap:

0% SF: Clearest soap, may feel stripping
1-2% SF: Good balance of clarity and mildness (recommended)
3% SF: Mild but may cloud over time
Above 3%: Will cloud and can separate

This is lower than bar soap because excess oils cause cloudiness and can go rancid in liquid soap.

Step 1: Formulate Your Recipe with SoapMath Calculator

1.1 Select Potassium Hydroxide (KOH) (Step 1 in Calculator)

This is critical - KOH creates liquid soap, not NaOH!

For liquid soap, select Potassium Hydroxide (KOH) from the lye type options. Note that the calculator also offers Dual Lye (NaOH + KOH) for cream soaps - see our Dual Lye Soap Guide.

1.2 Water Calculation

For liquid soap paste, use 25-33% lye concentration (3:1 to 2:1 water:lye ratio)

Remember: lye concentration and water:lye ratio are the same number expressed differently

25% lye concentration = 3:1 water:lye ratio
33% lye concentration = 2:1 water:lye ratio

KOH requires at least 1:1 solution (50% concentration) to dissolve, but for liquid soap paste, use lower concentration:

Recommended: 25-30% lye concentration (more water makes mixing easier)
This extra water helps with paste formation
You can use 33%, but paste will be thicker and harder to work with

1.3 Superfat

Set superfat to 0-2% (recommended: 1%)

Higher superfat clouds the soap
0% is acceptable for liquid soap
Maximum 3% if you don't mind cloudiness

1.4 Batch Size (Step 4 in Calculator)

Start with 500-1000g oils for your first batch

This creates about 1.5-3kg of paste
Paste dilutes 1:1 to 1:4 (paste:water) depending on desired thickness
Final yield: 3-12kg of liquid soap!

1.5 Additives (Step 5 in Calculator - Optional)

Step 5 offers optional enhancements like citric acid, additives, and water replacements. For liquid soap:

Citric acid: Skip for liquid soap (not commonly used)
Additives: Can add sodium lactate (1-2%) for clarity, or glycerin at dilution stage
Water replacements: Not recommended - stick with distilled water for clarity

For your first liquid soap, skip this step entirely.

1.6 Select Your Oils (Step 6 in Calculator)

Beginner-friendly liquid soap recipe:

Coconut Oil: 50%
Castor Oil: 20%
Sunflower Oil: 20%
Olive Oil: 10%

For gentler, conditioning liquid soap:

Coconut Oil: 35%
Castor Oil: 25%
Sunflower Oil: 20%
Hemp Oil: 15%
Olive Oil: 5%

For maximum lather, clear soap:

Coconut Oil: 60%
Castor Oil: 30%
Sunflower Oil: 10%

Click "Add" after each oil selection.

1.7 Calculate Formula

Click "Calculate Formula" to get:

Exact KOH amount needed
Water amount for paste
Individual oil weights

DO NOT add fragrance yet - it goes in after dilution!

Step 2: Make the Soap Paste

Method 1: Slow Cooker (Recommended for Beginners)

Phase 1: Prepare KOH solution

Weigh water in heat-safe container
Weigh KOH in separate container
Work outside or in well-ventilated area
Slowly add KOH to water while stirring
Stir until dissolved (will get VERY hot, 180-200°F/82-93°C)
Set aside to cool to 160-180°F (71-82°C)

Phase 2: Prepare oils

Weigh all oils in slow cooker
Turn slow cooker to LOW
Melt solid oils if using any
Heat to 160-180°F (71-82°C) to match KOH solution

Phase 3: Combine and cook

Pour KOH solution into oils (both should be 160-180°F)
Stick blend for 10-15 minutes until thick trace
- - Paste method needs thick trace
- - Should be pudding-like consistency
- - May look curdled or separated - this is normal
Cover slow cooker and cook on LOW
Check every 30 minutes, stirring
Cook for 1-4 hours total until paste is clear and tests done

What you'll see during cooking:

First 30 min: Looks separated or curdled
1 hour: Starting to come together
2 hours: Turning translucent
3-4 hours: Translucent paste, taffy-like

Method 2: Stovetop (Faster)

Same process but use double boiler on stovetop instead of slow cooker. Requires more attention to prevent scorching.

Method 3: Room Temperature (Advanced)

Bring to thick trace, pour into container, cover, and let sit for 1-2 weeks. Paste will cure without heat. Requires patience.

Step 3: Test Your Soap Paste

Clarity test:

Dissolve small amount of paste (1g) in hot water (10g)
Let cool to room temperature
Should be clear or slightly cloudy
If milky white, needs more cooking time

Zap test:

Touch tiny amount of paste to tongue
If it "zaps" like a battery, it's still lye-heavy - cook longer
No zap = done!

pH test:

Dilute small amount in distilled water
Test with pH strips
Should be 9-10
Above 11 = lye-heavy, cook longer

Step 4: Dilute Your Paste

Dilution ratio depends on desired thickness:

Thin liquid soap: 1 part paste : 3-4 parts water
Medium liquid soap: 1 part paste : 2-3 parts water
Thick liquid soap: 1 part paste : 1-2 parts water

Hot Dilution Method (Faster)

Weigh your paste (e.g., 500g)
Decide dilution ratio (e.g., 1:2 for medium)
Calculate water needed (500g paste × 2 = 1000g water)
Heat water to 160-180°F (not boiling)
Add paste to hot water in chunks
Stir occasionally (don't create bubbles)
Let sit 4-12 hours until fully dissolved
Stir gently - paste will dissolve on its own

Cold Dilution Method (Slower)

Same process but use room temperature water
Takes 1-3 days for paste to fully dissolve
Stir once or twice daily
Very gentle, preserves fragrance better

Step 5: Clarify (Optional)

If soap is cloudy:

Let sit undisturbed for 1-2 weeks
Cloudiness/particles settle to bottom
Carefully pour clear soap off the top
Strain through cheesecloth if needed

Or accept the cloudiness - it doesn't affect performance!

Step 6: Add Fragrance and Additives

After dilution is complete:

Fragrance:

Essential oils: 0.5-2% of final diluted weight
Fragrance oils: Check IFRA limits for Category 9
- - If limit is very high (30%+), you don't need that much
- - Use 0.5-1.5% for well-scented soap
Add slowly, stir gently, test scent strength

Additives:

Glycerin (1-3%): Extra moisturizing
Vitamin E (0.5%): Antioxidant
Citric acid (0.1-0.5%): pH adjustment, clarity (WARNING: lowers pH - may need preservative)
Colorants: Liquid dyes work best

Mix gently - aggressive stirring creates bubbles that take days to settle!

Step 7: Bottle Your Liquid Soap

Let soap rest 1-2 days after adding fragrance
Check for separation - stir if needed
Pour into bottles - pump or squeeze bottles work best
Label with ingredients and date
Let rest 1-2 weeks before use (soap will thicken slightly)

Preserving Liquid Soap

Why We Recommend Preservative for All Liquid Soap

We recommend adding a broad-spectrum preservative to ALL liquid soap, even though traditional high-pH soap (pH 9-10+) is technically self-preserving.

Here's why:

Water activity is HIGH (0.95-0.98): Liquid soap has plenty of "free" water available for microbial growth. The high pH (9-10) creates an alkaline environment that inhibits most microbes. However, pH can drop over time.
Real-world conditions compromise pH: Using soap in the shower introduces water contamination, adding oils or botanicals can lower pH, and storage conditions may affect pH over time.
Better safe than sorry: Preservatives provide insurance against pH drops and protect users if pH drifts below 9.

Recommended Preservatives for Liquid Soap

Not all preservatives work at high pH! Choose from these high pH compatible options:

Best options (work up to pH 12):

Liquid Germall Plus (0.1-0.5%) - Most popular, effective broad-spectrum
Optiphen Plus (0.75-1%) - Another excellent high-pH option
Suttocide A (0.2-0.5%) - Works well at high pH

DO NOT use these (ineffective at pH 9-10+):

Phenoxyethanol alone (only works below pH 8)
Leucidal (only works below pH 6)
Most "natural" preservatives (check pH range)

When to Add Preservative

Add preservative after dilution and after cool-down (below 40°C/104°F):

Dilute your paste completely
Add any fragrance or additives
Let cool to room temperature or slightly warm
Add preservative according to manufacturer's rate
Stir gently but thoroughly
Bottle and label

pH Testing is Still Important

Even with preservative, monitor pH:

Check pH:

After making and diluting soap
After adding all ingredients
1 week after bottling
If you notice any changes

Target pH:

Hand/body soap: 9-10 (high pH soap)
Facial cleanser: 8-9 (gentler)

If pH is not in target range:

Raise pH: Add small amounts of KOH solution
Lower pH: Add small amounts of citric acid solution
Retest after adjustments
Ensure preservative is effective at final pH

Preventing Contamination

Preservative works best when combined with good practices:

Sanitation:

Use distilled water only (never tap water)
Sanitize all bottles with 70% alcohol before filling
Clean equipment thoroughly between batches
Work on clean surfaces

Storage:

Store away from direct sunlight
Keep in cool, dry place
Use pump bottles instead of open jars
Don't "top off" bottles - use fresh soap

Usage:

Don't introduce water into soap bottle
Keep shower spray away from bottles
Don't share bottles if possible
Replace every 6-12 months

Troubleshooting Liquid Soap

If you see this...	What's happening...	Solution
Paste won't reach trace	Not enough mixing, temperature too low, or wrong lye type	Stick blend for longer (up to 30 minutes); ensure both phases are 160-180°F; verify you used KOH not NaOH
Paste stays cloudy/white after cooking	Not fully saponified or needs more cooking time	Cook longer (30 min-1 hour more); do zap test - if it zaps, keep cooking; ensure slow cooker is on LOW not WARM
Diluted soap is cloudy	Superfat too high, wrong oils used, or unsaponified oils	Use 0-2% superfat next batch; avoid solid fats; let soap sit 1-2 weeks for particles to settle, then decant clear portion
Diluted soap separates	Too much superfat or oil phase separating	Reduce superfat to 0-1%; add small amount of glycerin (1-2%); gently reheat and stir to recombine
Soap is too thin/watery	Too much water in dilution	Add more paste; or simmer gently to evaporate water (don't boil); or use as-is for hand soap
Soap is too thick/gel-like	Not enough water in dilution or natural thickening	Add more distilled water; heat gently and stir; or leave as-is (some prefer thick consistency)
Paste won't dissolve during dilution	Not enough time or water not hot enough	Be patient - can take 12-24 hours; use hotter water (160-180°F); break paste into smaller pieces
White floaties or particles	Undissolved paste, stearic spots, or crystallization	Strain through cheesecloth; reheat gently; let settle and decant; usually harmless
Soap zaps after cooking	Still lye-heavy, not fully saponified	Cook longer (1-2 more hours); retest; never use soap that zaps - it's unsafe
Soap turned dark/amber color	Natural reaction with sugars in oils or overheating	Normal for some oils; doesn't affect performance; avoid overheating above 200°F
No lather	Not enough coconut oil or too much superfat	Increase coconut oil to 40-60% next batch; reduce superfat to 0-1%; add 1-3% sugar to diluted soap to boost lather
Soap is too harsh/drying	Too much coconut oil or 0% superfat	Reduce coconut to 35-50%; increase superfat to 1-2%; add glycerin (2-3%) to diluted soap
Fragrance faded	Added fragrance too early or volatile fragrance	Add fragrance after dilution; use fragrance oils rated for soap; increase amount by 0.5%
Soap developed mold	pH too low or contamination	Check pH (should be 9-10); if below 9, add preservative; always use distilled water; sanitize bottles

Advanced Liquid Soap Techniques

Creating Different Soap Products

Hand Soap (thin consistency):

Dilute 1:3 or 1:4 (paste:water)
Add 1-2% glycerin
Light fragrance (0.5-1%)
Antibacterial option: add 0.5-1% tea tree essential oil

Body Wash (medium consistency):

Dilute 1:2 or 1:3 (paste:water)
Add 2-3% glycerin
Add 1% jojoba or sweet almond oil (after dilution)
Fragrance 1-1.5%

Dish Soap (thin, high cleansing):

Use high coconut oil recipe (60-70%)
Dilute 1:4 (paste:water)
Add 1-2% washing soda for extra grease cutting
Fragrance optional (lemon works well)

Foaming Hand Soap:

Dilute 1:4 or 1:5 (paste:water) - very thin
Use foaming pump dispenser
Add 1% glycerin
Light fragrance only

Adjusting Lather

For more lather:

Increase coconut oil (up to 60%)
Increase castor oil (up to 30%)
Add 1-3% sugar to diluted soap
Add 1% glycerin

For creamier lather:

Add 10-20% shea butter (expect cloudiness)
Increase castor oil to 25-30%
Add 2% glycerin

Adjusting Thickness

To thicken:

Add more paste
Add 0.5-1% salt (sodium chloride) - test first, can thin in some cases
Add 0.5-1% guar gum or xanthan gum (pre-mix with glycerin)
Simmer to evaporate water

To thin:

Add more distilled water
Heat gently while stirring
Add slowly - can't remove water easily once added

Storage and Shelf Life

Soap paste storage:

Store in airtight container
Lasts indefinitely if kept dry
No refrigeration needed
Can store for months before diluting

Diluted soap storage:

Store in cool, dry place
Away from direct sunlight
Shelf life: 1-2 years (if pH is 9-10)
With preservative and pH below 9: 6-12 months

Signs of spoilage:

Mold growth (fuzzy spots)
Rancid smell
Color change
Separation that won't remix

Scaling Your Recipe

For paste: Same as bar soap - use calculator for different batch sizes.

For dilution:

Water needed = Paste weight × dilution ratio

Example: 1000g paste, 1:2 ratio

Water needed: 1000g × 2 = 2000g
Final yield: 3000g liquid soap

Batch size suggestions:

Small test batch: 250g oils → ~750g paste → 1500-3000g liquid soap
Standard batch: 500g oils → ~1500g paste → 3000-6000g liquid soap
Large batch: 1000g oils → ~3000g paste → 6000-12000g liquid soap

Cost and Efficiency

Why liquid soap paste is economical:

500g oils creates 1.5kg paste
Paste dilutes to 3-6kg liquid soap
Commercial liquid soap: ~$3-8 per liter
Homemade cost: ~$0.50-2 per liter

Compared to bar soap:

Liquid soap uses slightly more oils per use
But reduces waste (no melting bar in dish)
More convenient for hand washing
Great for refilling pump bottles

Tips for Success

For your first batch:

Use simple recipe (coconut, castor, sunflower)
Make small batch (500g oils)
Use slow cooker method
Accept cloudiness - focus on learning process
Don't add fragrance until dilution

As you gain experience:

Experiment with oil blends
Try different dilution ratios
Create custom scent blends
Make specialized soaps (dish soap, body wash)
Adjust pH for specific uses

Pro tips:

Make paste in bulk, dilute as needed
Keep paste on hand for quick soap making
Test fragrance in small amount first
Label everything (paste batch, dilution ratio, date)
Take notes for recipe refinement

Frequently Asked Questions

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