Bastille Cold Process Soap Recipe

Discover the perfect balance between the mildness of pure castile soap and the lather and hardness of modern soaps. Bastille soap, also called Castile-style or Castile-blend soap, uses 70-80% olive oil combined with a small amount of coconut oil for lather and hardness. This recipe creates a bar that maintains the gentle, moisturizing properties of castile while producing more abundant lather and creating a firmer, longer-lasting bar. Perfect for all skin types, bastille soap offers the best of both worlds.

Ingredients

Oils & Butters

• 40 oz (1134g) olive oil (extra virgin or pure)
• 14.0 oz (397g) coconut oil

Lye Solution

• 7.6 oz (215g) sodium hydroxide (NaOH)
• 16.0 oz (454g) distilled water

Additives (Optional)

• 0.6 oz (17g) fragrance oil or essential oil
• Mica or oxide colorant (0.25 tsp—optional)
• Dried botanicals like calendula or chamomile (0.25 oz)

Equipment Needed

• Digital scale accurate to 0.1 oz
• Two stainless steel pots
• Stainless steel spoon
• Stick blender (immersion blender)
• Thermometer
• Soap mold (deep loaf mold preferred)
• Safety goggles and gloves
• Soap cutter or serrated knife
• Vinegar (for cleanup)
• Optional: spray bottle with rubbing alcohol

Instructions

Step 1: Prepare Your Safety Equipment

Don safety goggles and chemical-resistant gloves. Set up your workspace with all equipment ready. Ensure adequate ventilation. Keep vinegar nearby for lye spills.

Step 2: Mix the Lye Solution

Pour 16 oz of distilled water into a heat-safe stainless steel pot. Slowly add 7.6 oz of sodium hydroxide while stirring constantly with a stainless steel spoon. The solution will heat to 160-180°F as the lye dissolves. Set aside to cool to 100-110°F.

Step 3: Prepare Oil Blend

In a separate pot, combine:

• 40.0 oz (1134g) olive oil
• 14.0 oz (397g) coconut oil

Stir to combine the oils. The coconut oil may be solid; it will melt as you gently heat the mixture. Slowly heat the oil blend to 100-110°F, stirring occasionally.

Step 4: Combine at Proper Temperature

Once both the lye solution and oils reach 100-110°F, slowly pour the lye into the oils while stirring steadily. Continue stirring for 1-2 minutes to ensure complete incorporation. The mixture will begin to trace.

Step 5: Stick Blend to Light Trace

Using your stick blender, pulse for 30 seconds, then stir by hand for 1-2 minutes. Continue this alternating pattern for 12-15 minutes until you reach light trace. Bastille traces more quickly than pure castile but more slowly than blended-oil recipes.

Step 6: Add Fragrance

At light trace, add your 0.6 oz of fragrance oil or essential oil blend. Stir thoroughly for 1-2 minutes. Bastille soap accepts fragrance well and the scent develops nicely during cure.

Step 7: Add Color and Botanicals (Optional)

If using colorant, add it dispersed in a small amount of oil to prevent streaking. If adding dried botanicals, sprinkle them into the batter and stir gently to incorporate. The botanicals will add visual appeal and texture to the finished bar.

Step 8: Pour Into Mold

Pour the soap batter into your prepared mold. Use a spatula to smooth the top. If desired, sprinkle additional dried botanicals on top for visual interest. Spray lightly with rubbing alcohol to remove air bubbles.

Step 9: Insulate the Mold

Wrap the mold with blankets or towels to insulate and encourage gel phase. This creates a more consistent color and texture throughout the batch.

Step 10: Wait 24-48 Hours

Leave the soap undisturbed for 24-48 hours. The saponification reaction will occur naturally. The insulation helps promote gel phase, resulting in a more translucent, smooth bar.

Step 11: Unmold the Soap

After 24-48 hours, carefully remove the soap from the mold. Bastille soap should be firmer than pure castile but softer than blended-oil soaps. If still soft, wait another 12-24 hours.

Step 12: Cut Into Bars

Using a soap cutter or sharp serrated knife, cut the loaf into 24 equal bars. Bastille soap cuts cleanly but requires a bit more pressure than modern blended-oil soaps. Work steadily for the best results.

Step 13: Air Cure

Place bars on a well-ventilated rack with space between each one. Cure in a cool, dry location (60-75°F) for 4-6 weeks. Bastille soap improves with time; some makers cure for 8 weeks for an even harder, longer-lasting bar.

Tips for Success

• The olive oil to coconut oil ratio is key to bastille's success—don't change it significantly
• Extra virgin olive oil creates a greenish bar; pure olive oil is paler
• Bastille traces between pure castile (slow) and modern soaps (fast)—monitor carefully
• The soap will improve in hardness and mildness during cure time
• Bastille produces a creamy, luxurious lather—not as abundant as modern soaps but very pleasant
• This soap is excellent for sensitive skin while still being practical for daily use
• The longer you cure, the milder and harder the finished bar becomes
• Bastille bars typically last longer than modern blended-oil soaps

Variations

• Bastille with honey: Add 2 tbsp of honey at trace for extra conditioning
• Scented bastille: Add lavender, rose, or vanilla fragrance for a spa-like bar
• Bastille with oatmeal: Add 0.5 oz of finely ground oatmeal at trace for gentle exfoliation
• Herbal bastille: Add dried herbs like chamomile or rose petals for visual appeal

Cost Breakdown

Estimated Cost per Bar: $0.44

Related Recipes

• Castile Olive Oil Soap - Pure 100% olive oil traditional castile
• Basic Cold Process Soap - Modern blended-oil soap for comparison
• Shea Butter Moisturizing Soap - Alternative moisturizing formula

Traditional Soap Making: Bastille soap represents the evolution of soap making from pure castile toward modern formulas. Historically created in regions where both olives and coconuts became available through trade, bastille soap offers a perfect compromise: the mildness of castile combined with the practicality of modern soap. It's particularly popular among artisanal soapmakers who value tradition and skin-friendly formulation.

Skin Profile: Bastille soap is ideal for those seeking a middle ground between extreme mildness and modern practicality. It's gentle enough for sensitive and reactive skin while producing enough lather for satisfying daily cleansing. The long cure time creates a bar that's both mild and durable, making it an excellent all-purpose soap for the whole family.