Hot Process Soap Making: Step-by-Step Instructions for Beginners

Hot process soap making is another way to make beautiful, natural, handmade soap using oils, lye, and water. If you’ve already tried cold process soap, you will find that many of the steps are similar. The biggest difference is that hot process soap is cooked after the oils and lye solution have been mixed.

This extra heat speeds up saponification, the chemical reaction that turns oils and lye into soap.

While cold-process soap is usually poured into molds shortly after reaching trace, hot-process soap is cooked first and then spooned into molds.

There are three common methods of making hot process soap:

• Crock Pot Hot Process (CPHP)
• Double Boiler Hot Process (DBHP)
• Oven Hot Process (OHP)

Each method has advantages, but for beginners, I recommend starting with the crock pot method. It’s easier to watch your soap as it cooks, and the temperature is generally easier to manage.

If you are completely new to soap making, read my guide on  How to Make Cold Process Soap at Home first. It explains the basics of soap-making, working with lye, combining oils, and recognizing trace.

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What Is Hot Process Soap Making?

Hot process soap is made by combining oils with a sodium hydroxide (lye) solution, just as you would when making cold process soap.

The difference comes after the soap reaches trace.

Instead of immediately pouring the soap into molds, you heat it up.

As it cooks the soap mixture becomes thicker, develops a glossy surface, and may eventually resemble petroleum jelly.

Once it has finished cooking, you can add suitable fragrances, colours, or other ingredients before transferring it into molds.

Hot process soap generally has a more rustic appearance than cold process soap, but that is part of its handmade charm.

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Advantages of Hot Process Soap Making

There are several reasons why some soap makers enjoy using the hot process method.

1. Faster saponification

Because heat is applied during the soap-making process, most of the saponification happens before the soap is molded.

2. Fragrance can be added after cooking

Essential oils and fragrance oils are generally added after the main cooking stage. This can help with certain fragrances, although the remaining heat may still cause evaporation or other changes.

3. Soap can often be unmolded sooner

Depending on the recipe, hot-process soap may be ready to remove from the mold within approximately 12–24 hours.

4. Natural, rustic appearance

Hot process soap has a textured, handmade appearance that many people enjoy.

5. Several cooking methods

You can make hot-process soap using a crock pot, double boiler, or oven.

Does Hot Process Soap Need to Cure?

Yes, I still recommend curing hot-process soap.

Although the cooking process speeds up saponification, the finished soap still contains water that needs time to evaporate.

Allowing your soap to cure for approximately 2–4 weeks, or longer depending on the recipe, helps produce a harder bar that lasts longer.  The longer the cure the harder the bar gets.

If you’re wondering why curing is important, read my article on How Long Should Handmade Soap Cure?.

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Disadvantages of Hot Process Soap Making

Hot process soap also has a few disadvantages.

• The soap is thicker and more difficult to pour into molds.
• Creating decorative swirls can be challenging.
• Cooking requires additional time and attention.
• Overheating can cause the soap to become dry or crumbly.
• Some essential oils and fragrances may still be affected by heat.
• The finished bars are usually less smooth than cold process soap.

If you enjoy making decorative soap with delicate swirls and layers, cold-process soap is a better choice.

However, if you like rustic-looking bars and enjoy experimenting with different soap-making methods, hot-process can be worth trying.

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Equipment Needed for Hot Process Soap Making

You can use the same equipment used for cold-process soap-making, along with a suitable cooking vessel.

Here’s what you’ll need:

• Crock pot or slow cooker
• Accurate digital kitchen scale
• Stainless steel or lye-compatible containers
• Stick blender
• Silicone spatula
• Digital thermometer
• Soap molds
• Safety goggles
• Chemical-resistant gloves
• Long sleeves and closed-toe footwear

Always use equipment compatible with sodium hydroxide. Never use aluminum because it reacts with lye.

I also recommend keeping soap-making equipment separate from any other equipment used to prepare food.

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Recommended Soap-Making Supplies

One of the most important tools you can own is an accurate digital scale. Measuring your ingredients by weight rather than volume is essential when working with lye.

If you need one, you can look at Digital Kitchen Scales for Soap Making on Amazon.  This is the one I use.

A good silicone mold works well because hot-process soap can be quite thick when you’re ready to mold it.

You can find Silicone Loaf Soap Molds on Amazon.

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How to Make Hot Process Soap in a Crock Pot

The crock pot method is probably the easiest hot process method for beginners.

A slow cooker provides a convenient source of heat, and you can watch the soap throughout the cooking process.

I recommend beginning with a small batch and leaving plenty of room in the crock pot because soap can expand while cooking.

Step 1: Prepare Your Soap Recipe

Start with a properly calculated soap recipe.

You can use many cold-process recipes for hot-process soap, although the water amount and cooking procedure may need to be adjusted.

The recipe should contain accurately measured amounts of:

• Oils and butters
• Sodium hydroxide (lye)
• Distilled water
• Optional fragrance or colour

Always check the recipe using a reliable soap calculator before making a batch.

Different oils contribute different properties to handmade soap, including hardness, lather, and conditioning qualities.

For more information, read my guide on Soap Making Oils: 10 of the Best Oils to Use.

Step 2: Prepare Your Lye Solution

Be sure to wear safety goggles, gloves, and protective clothing before handling lye.

Work in a well-ventilated area away from children and pets.

Carefully measure the distilled water and weigh the sodium hydroxide in separate, suitable containers.

Slowly add the lye to the water while stirring until it dissolves.

Always add lye to water, never water to lye.

The solution will become very hot and initially release irritating fumes. Avoid breathing these fumes and allow the solution to cool as required by your recipe.

Never leave your lye solution unattended where someone could accidentally touch or spill it.  I put the lye container in my sink in the soap room.

Step 3: Melt Your Oils

Place the measured solid oils and butters into the crock pot.

Turn the crock pot to low and allow the oils to melt.

Once the solid oils have melted, add your liquid oils and stir until everything is evenly combined.

Avoid overheating the oils.

Step 4: Combine the Oils and Lye Solution

When the oils and lye solution have reached suitable temperatures for your recipe, carefully pour the lye solution into the oils.

Using your stick blender, blend in short bursts, alternating with gentle stirring.

Continue until the soap batter reaches a stable light to medium trace.

Trace occurs when the oils and lye solution have emulsified, and the mixture starts to thicken.

Step 5: Cook the Soap

Once the soap has reached trace, cover the crock pot and continue cooking on low.

The cooking time depends on your recipe, batch size, and crock pot.

Many batches take approximately 45–120 minutes, although cooking times can vary considerably.

As the soap cooks, you’ll notice several changes.

First, the edges may begin to thicken.

Next, the soap may become glossy and develop a gel-like appearance.

Eventually, much of the mixture may look thick and somewhat translucent, similar to petroleum jelly.

Keep an eye on the crock pot while soap is cooking.

Soap can expand as it heats, particularly if the temperature becomes too high.

If the soap begins to rise toward the top of the crock pot, turn off the heat and allow it to settle.

Stir gently when necessary to encourage even cooking, taking care to avoid splashing the hot, caustic mixture.

Step 6: Check the Finished Soap

Once the soap has finished cooking, it should have a relatively uniform consistency.

The mixture is usually thick, glossy, and somewhat translucent, although the exact appearance depends on the recipe.

Remember that appearance alone cannot tell you whether a batch contains excess lye.

Accurate measurements, correct formulation, and complete mixing are essential.

Step 7: Add Essential Oils, Fragrance, or Colour

Once the soap has finished cooking, turn off the crock pot and allow it to cool sufficiently for your chosen additives.

Many soap makers add fragrance when the soap has cooled to around 60°C (140°F) or below, but the appropriate temperature depends on the particular fragrance and recipe.

Always follow the supplier’s recommended usage rate and any temperature guidance.

Some essential oils are more sensitive to heat than others, and certain fragrances may still evaporate or change when added to hot soap.

If you’re looking for ideas, read my guide on What to Scent Soap With.

You can also add suitable soap colourants at this stage.

For inspiration, visit Soap Coloring Ideas for Handmade Soap.

If you enjoy experimenting with natural colours, you may find Soap-Making Clays and Natural Colourants on Amazon useful.

Step 8: Spoon the Soap Into Your Mold

Unlike cold-process soap, hot-process soap is usually too thick to pour smoothly.

I find the best way is to use a silicone spatula, or large spoon to transfer the soap into your prepared mold.

Work carefully because the soap may still be extremely hot.

Press the soap into the corners of the mold to help eliminate air pockets.

Gently tap the mold on a sturdy surface to help settle the mixture.

You can smooth the top with a spatula or leave it textured for a rustic appearance.

Step 9: Unmold and Cut Your Soap

Allow the soap to cool and harden completely.

Many hot-process soaps can be unmolded within approximately 12–24 hours, but some recipes take longer.

Once the soap is firm enough, carefully remove it from the mold.

Use a soap cutter or knife to cut the loaf into individual bars.

Because hot-process soap can become quite hard as it cools, it’s a good idea to check the firmness rather than leaving it in the mold longer than necessary.

For evenly sized bars, you can use a Handmade Soap Cutter from Amazon.

Step 10: Cure Your Hot Process Soap

Even though hot process soap has already been cooked, I still recommend allowing it to cure.

Place your freshly cut bars on a drying rack in a cool, well-ventilated area.

Leave some space between the bars so air can circulate.

Allow the soap to dry for approximately 2–4 weeks, or longer if necessary.

During this time, excess water evaporates, helping the soap become harder and longer-lasting.

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Making Hot Process Soap Using a Double Boiler

The double boiler hot process method, often called DBHP, uses indirect heat to cook the soap.

Instead of placing the soap pot directly over a burner, it sits above a larger pot of simmering water.

This provides gentler heat and can help reduce scorching.

To make hot process soap using a double boiler:

1. Prepare your soap recipe and combine the oils and lye solution.
2. Blend the mixture until it reaches trace.
3. Place the soap mixture in a suitable lye-compatible pot over gently simmering water.
4. Monitor the mixture as it cooks, stirring carefully when needed.
5. Continue following a tested hot process procedure until cooking is complete.
6. Allow the soap to cool appropriately before adding fragrance or colour.
7. Spoon the soap into molds and allow it to harden.

Make sure the lower pot doesn’t boil dry, and avoid allowing water to splash into the soap mixture.

The double boiler method can work well, but it requires attention to maintain a suitable cooking temperature.

Making Hot Process Soap in the Oven

Oven hot process soap making, sometimes called OHP, uses the oven to provide the heat needed for cooking.

Some soap makers use oven temperatures around 100°C (212°F), but the correct temperature and cooking procedure depend on the recipe and equipment.

One older method involves preheating the oven, turning it off, and leaving the soap inside to finish cooking.

The problem with this approach is that every oven retains heat differently.

Some ovens cool quickly, while others remain hot for much longer.

For more reliable results, use a tested oven hot process procedure with controlled temperatures rather than relying on a fixed cooking time.

The general process involves:

1. Preparing the oils and lye solution.
2. Blending the mixture until it reaches trace.
3. Transferring the soap into a suitable oven-safe, lye-compatible container with room for expansion.
4. Cooking according to a tested oven hot process procedure.
5. Monitoring the soap throughout cooking.
6. Allowing it to cool appropriately before adding suitable additives.
7. Transferring the finished soap into molds.

Never use a tightly sealed container, and remember that hot soap can expand during cooking.

Although this method can be convenient, I prefer the crock pot method for beginners because it’s easier to observe the soap as it cooks.

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Hot Process vs. Cold Process Soap: What’s the Difference?

Both methods use oils and lye to create handmade soap, but the way the soap is processed is different.

Feature	Hot Process	Cold Process
Heating	Cooked after trace	Usually no added cooking heat
Texture	Thick and rustic	Smooth and pourable
Saponification	Accelerated by cooking	Continues after molding
Unmolding	Often 12–24 hours	Often 24–48 hours
Curing	Usually 2–4 weeks or longer	Usually 4–6 weeks or longer
Decorative swirls	More difficult	Easier
Equipment	Requires cooking equipment	No additional cooking equipment

If you enjoy making decorative soaps, cold process gives you more time to work with your batter.

Hot process is particularly useful if you prefer rustic-looking soap and want to complete most of the saponification process before molding.

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Common Hot Process Soap Problems and How to Avoid Them

Why Is My Hot Process Soap Dry and Crumbly?

Dry or crumbly soap can happen when the soap has been overheated, cooked too long, or made with an unsuitable amount of water.

Incorrect ingredient measurements can also cause problems.

If your soap becomes unusually brittle, check your recipe and measurements before using it.

Why Does My Hot Process Soap Have Air Pockets?

Hot process soap is thick, so air can become trapped when you transfer it into the mold.

To help prevent this, press the soap gently into the corners of the mold and tap the mold carefully to help the mixture settle.

Why Is My Soap Too Soft to Unmold?

Some soap recipes take longer to harden than others.

The oils used, water content, and cooking process all affect how quickly soap becomes firm.

Give the soap additional time if needed.

If the batch remains unusually soft or shows signs of separation, investigate the recipe and measurements.

Why Does My Hot Process Soap Look Rough?

A rough appearance is normal for hot process soap.

Because the mixture is thick when molded, it doesn’t settle as smoothly as cold process soap.

You can use a spatula to smooth the surface, but many soap makers enjoy leaving the tops naturally textured.

Can Hot Process Soap Seize?

Soap batter can thicken rapidly before or during cooking, especially if certain fragrances are added too early or the mixture becomes overheated.

Hot process soap also becomes naturally thick as it cooks, so not every thick batch has seized.

If you’re having trouble with soap batter becoming too thick too quickly, my article on How to Fix a Seized Soap Batch explains what can cause this problem and how to recognize it.

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Frequently Asked Questions About Hot Process Soap

Can I Use My Regular Cold Process Soap Recipe?

Many cold process recipes can be adapted for hot process soap.

However, the water amount and cooking procedure may need to be adjusted.

Always check your recipe with a reliable soap calculator before making it.

Can I Use Hot Process Soap the Next Day?

Hot process soap may have completed saponification during cooking, but that doesn’t mean it has finished curing.

I recommend allowing the bars to dry for several weeks to improve hardness and longevity.

Is Hot Process Soap Better Than Cold Process Soap?

Not necessarily.

Both methods can produce excellent handmade soap.

Hot process speeds up saponification, while cold process generally gives you more time to create decorative designs.

Do I Need a Special Crock Pot?

You don’t need a crock pot specifically manufactured for soap making.

However, it should have a suitable lye-compatible insert, an appropriate low-heat setting, and enough room for the soap to expand.

I recommend dedicating your crock pot to soap making rather than using it for food preparation afterward.

Can I Add Essential Oils After Cooking?

Yes, essential oils are commonly added after the cooking stage.

Allow the soap to cool to a suitable temperature and always follow the essential oil supplier’s recommended skin-safe usage rate.

Does Hot Process Soap Last as Long as Cold Process Soap?

Both methods can produce long-lasting bars.

The oils used, recipe formulation, water content, and curing time have a greater influence on bar longevity than the method alone.

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Final Thoughts on Hot Process Soap Making

Hot process soap making is another method worth learning if you enjoy making your own natural handmade soap.

Although it requires an additional cooking stage, many of the basic steps are similar to cold process soap making.

Of the three methods, I recommend starting with the crock pot method because it’s easier to observe the soap as it cooks.

Once you’re comfortable with the process, you can experiment with different oils, natural colours, and fragrances.

If you’re interested in trying other methods, you might also enjoy my articles on Melt and Pour Soap and How to Make Goat Milk Soap.

Whatever method you choose, remember that accurate measurements, proper lye handling, and sufficient curing time are important parts of making good handmade soap.

Soap Making Safety Disclaimer: Soap making involves sodium hydroxide (lye), which can cause serious burns. Always wear suitable protective equipment, work in a well-ventilated area, and use a properly calculated recipe. Cooking time, appearance, and pH strips alone cannot confirm that soap is free from excess lye. If a batch has measurement errors, separation, or other signs of a problem, do not use it until its safety has been established.

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