How to calculate the yield from a soap recipe

When you’re making a soap recipe, one thing you might wonder is how to calculate the yield from your soap recipe.

Yield noun – the amount or quantity produced or returned.

There is a really easy way to calculate the yield from any recipe. However, some real world variables will affect the calculation, and in practice, you will find that the yield from any given soap recipe is a bit less than it ought to be.

Why don’t soap calculations produce an exact weight?

A viscous liquid is thick. As a liquid gets more viscous, it pours less readily, until eventually a liquid can be so viscous it doesn’t pour at all (like whipped cream). Soap is a liquid which is viscous, whether it’s melt and pour or a cold process soap that has reached trace. A light trace is less viscous than a heavy trace, but both are more viscous than water.

When you try to pour a viscous liquid, some of it will stick to the sides of the bowl or jug. It will also stick to your stick blender or stirring spoon. This results in a loss of about 10-20g of soap batter per batch. If you are making a small batch such as a single bar of soap, you can lose a significant amount.

The best way to compensate for this loss is to make a bigger batch, because you will not lose much more batter from a larger batch than from a smaller one.

With that in mind, here is how you calculate soap yield:

Add together the weight of all the solid ingredients. Convert water into grams (1ml of water weighs 1g). Other liquids don’t convert 1:1, because a ml is a measure of capacity while a gram is a measure of mass, and the mass of a given capacity is dependent on the density of its molecules. Oils have long chains of molecules, where water has small molecules made of only three atoms, so more water molecules fit into the same space as any oil, so water will always be heavier and more dense than oil for the same capacity.

Confused? Here’s how it works on a practical level. With liquid oils, such as avocado oil, you will need to weigh them separately. Do this before you mix your ingredients together. With electric scales (recommended for soaping), you can do this by turning on your scales and putting an empty container on top, then pressing “tare”. This will set the scales to ignore the mass of the container and just weigh what you put inside it. Next, pour your oil into the container. This will tell you how much it weighs. Add this to the mass of all the other ingredients and this will tell you the total yield of your soap recipe.

Lye dissolves in water, so do I need to weigh it?

Yes. This is because, when you add the lye to the water, even though it dissolves, it is still in the container. The mass of the water increases by the mass of the lye. Any time something soluble (like salt, sugar, or sodium hydroxide lye) is dissolved in water, the mass doesn’t go anywhere.

You can put this to the test if you want to do some at-home chemistry by getting a cup of 100ml water, stir in 50g of salt, and weigh the total mixture. You’ll see the liquid will now weigh 150g and it will have noticeably increased in volume, too. This is because of one of the laws of physics which explain how the universe works.

Example:

Melt and pour recipe (taken from my Easy AHA exfoliating melt and pour soap recipe which you can find here). These are the ingredients:

10 ml Cherry kernel oil

90g Melt and pour soap base

1 ml Cherry blossom fragrance

A pinch of sliced up loofah

The cherry kernel oil needs to be weighed. It weighs 8 grams. Add this to the melt and pour soap base and we get 98 grams. It wouldn’t work to try to weigh 1ml of fragrance so we will round it up to 1 gram although it’s more like 0.9g.

In a higher yield recipe (e.g. making a kilo of soap) we would use a lot more fragrance so we would be able to weigh it but here it will not make much difference. So our total is 99g. In a 100g soap mold, this leaves a tiny bit of room for the sliced up loofah to go slightly under the surface of the soap without it spilling over the mold.

90g + 8g + 1g = 99g

So that’s how to calculate the yield for a soap or cosmetics recipe!

PS I’m super excited that my lye just arrived, so I’ll be trying out some cold process soapmaking as soon as my new stick blender gets here (mine died last year before the first lockdown), and I’ll be sure to share my makes (and fails… part of the learning process) as I move into this awesome new world of handmade soapmaking!

How to get a swirl effect in melt and pour soap

A lot of soapmakers tell you that you can’t get nice colour effects in melt and pour soap. They are wrong. Today I am going to share some of the colour effects I’ve achieved using swirls and layering techniques in melt and pour soap, and explain how you can do them too. Once you’ve tried it out, you’ll have beautiful soaps crafted artistically, just like in cold process soaps!

What is a swirl?

A swirl is where you have more than one colour in a soap, and usually you would spin it e.g. on a Lazy Susan. What is a Lazy Susan, I hear you ask. A Lazy Susan is one of those plate things that people used to use for Thanksgiving in the 1970s because you can spin it around instead of passing the carrots across the table… which is pretty lazy, hence the name.

A Lazy Susan a bit ugly on the dining table and in this day and age of Instagram and Martha Stewart, people tend to have a nice centrepiece in the middle of the table and just pass the carrots to each other. So people dumped their Lazy Susans in the garage and now you can use it to make soap instead! At least, you can if you are making cold process soap.

It doesn’t work so well in melt and pour. I suspect part of the reason why some cold process soapers look down on melt and pour is because they try to do things the exact same way you would do them in cold process, then they decide it’s the soap that’s the problem when it goes wrong.

There is absolutely a way to get a swirl effect in melt and pour, it’s just you don’t swirl it the same way as you would swirl a cold process soap!

How do you swirl in melt and pour?

To get a swirl effect, I use mica powder colours. I love these because they are available in vivid shades. They have a nice shimmer when you use them in high concentrations. Best of all, they show up really well in melt and pour soap. Colourants have to work extra hard in white melt and pour because, as you’ll know if you have ever done cold process, soap isn’t naturally white. The white colour comes from the addition of titanium dioxide, which can nix your other colour choices, especially if you want natural colours. Clays etc struggle in white melt and pour soap. Mica is a natural mineral so it’s a great all-rounder.

Melt your soap and split it into two separate jugs.

In a separate jug, mix your mica with a little rubbing alcohol (if you have no alcohol, you can put the mica directly into one of the jugs of melted soap as this will dissolve in melt and pour, but for colour effects, you get more control over the outcome if you mix the colour up separately because then you can add a little at a time to one of your jugs of soap). You will want about 2 teaspoons of alcohol to half a teaspoon of mica. You can use more alcohol than this, but it will start to overpower the scent of the soap very quickly.

Add a little of the dissolved colour to one of your jugs of soap and stir it in. Add more gradually until you get the colour you want. For a melt and pour swirl, I find it works best if the two colours of soap you use for the swirl are high-contrast, so, quite far apart e.g. black and white, bright pink and white, etc.

Pastels and white don’t tend to show up very well in a melt and pour swirl, but you could do one jug with some pastel and the other jug with a very intense colour, or a contrasting colour. I did quite a nice pink/dark pink strawberry melt and pour soap with pastel pink and vivid Barbie pink.

Once your colours are mixed up, let the soap cool to about 38 degrees celsius (about 100 fahrenheit). You can test this with an infrared thermometer if you have one, or you can tell if the soap has cooled enough because it starts to thicken very slightly. An infrared thermometer doesn’t need to touch the soap, making it ideal for soaping which can be hard to clean out of a regular thermometer. You may have to stir every few seconds to stop a skin forming on the top of the soap (don’t wait until the skin has formed, if that gets into your swirl it won’t look great). You will probably also need to pour your soap quickly, unless you live somewhere hot with the air conditioning turned off, like Malaysia, or a campervan in the Scottish summertime.

Once the soap is at the right temperature, pick up both jugs at the same time. Pour them into the mould from opposite corners. Where they meet, you should get a nice effect, you can emphasize this by moving both jugs in a clockwise direction (or anti-clockwise. As long as they both go the same way). You may have to practice this a bit to not just mix the two colours when you pour into the mould.

You might be wondering if you can make swirls with clay in melt and pour. You can, but the colours from clays don’t come out very strong so the contrast won’t be there. Indigo powder or charcoal powder could work very well, however, if you contrasted the dark colour with a lighter one like yellow French clay. The benefit of adding charcoal or clay to the soap is that your scent will work better, too, so it’s worth experimenting with using these natural colourants in your soaps!

What is a layer?

In cold process soap, this is where you pour one layer of soap (that’s been blended to medium trace) in one color, then pour another in another colour, often using zig-zag-type movements to get the colour to move around. To get a swirl in cold process, you pour your soap in lots of layers before putting your soap mould on a lazy Susan and spinning it. However, this requires you to work with thicker soap than you can easily get in melt and pour (because melt and pour is chemically different to the trace stage of cold process, it behaves differently and the viscosity is nowhere near the same). In cold process, the layers stay together because after you’ve poured them, the soap gets hot (saponification is an exothermic reaction which means it gives out heat) while it sets. In melt and pour soap, once you’ve poured it, all that happens is it cools down. So because the chemical reaction has already taken place before you ever get your block of melt and pour soap, the soap itself isn’t able to “cook” itself into a solid bar of soap. So in melt and pour, if you try and layer the same way you would in cold process, it won’t work. Your soap will just fall apart.

How do you layer in melt and pour?

This is a surprisingly controversial topic because people who don’t make melt and pour tend to believe you can’t layer it. But you can! And it’s surprisingly simple.

There are actually two ways to layer melt and pour soap. The traditional method and the one I’ve discovered. One is a lot better than the other. 😉 #sassysoapmaking

The first, less good method is to pour a layer, let it set, spray alcohol on it right before pouring the next layer. This makes your soap smell of alcohol because melt and pour doesn’t evaporate any alcohol in the mixture because it doesn’t go through gel phase. Yucky drunk soap.

The Double Melt Method

This second method, which I call the Double Melt method (patent pending… jk haha), produces a nicer result but you need to watch the soap closely to get it right. You will need a microwave for this.

Layer your soap by pouring, letting it form a decent skin (it should flex like a trampoline when you gently press down on it) and pouring the next layer, over and over until you have a full mould of soap.

Next, turn your microwave down to its defrost setting. Put the soap mould inside and turn it on for about 20 seconds for individual bars of soap or about 40-60 seconds for a big loaf mould (assuming your microwave is a standard 750 watt one). This should provide just enough heat to get the layers to melt together. You might get a little colour bleed between layers with this method.

Let the soap cool down and harden for about 1 hour before unmoulding it, that way if you’ve heated it too much, it will set fully.

I’ve gone into more detail on layering with the Double Melt Method in this separate article, including what to do if it all goes wrong (and my soapy disaster when I messed this up).

My lavender essential oil doesn’t smell strong in soap

This article aims to help you get the perfect lavender fragrance in your soap – every time! Be sure to also check out my 10 ways to make your essential oil show up in your soap for more tips!

Lavender is such a strong fragrance in the plant, you would expect it to be the ideal candidate for a good, intense soap scent, especially in melt and pour, where essential oils are usually stronger than in cold process. Instead, I’ve found homemade soap often seems to absorb lavender essential oil, so the homemade soap doesn’t smell strong enough.

Eek!

There are several types of lavender; the most common are French lavender and Bulgarian lavender, both of which use the Latin name Lavandula Angustifolia. French lavender essential oil is more expensive but Bulgaria now produces most of the world’s lavender oil, so you are more likely to find this in shops.

There are over 400 different species of lavender worldwide, which can have different potency and fragrance, but the commonest is still Lavandula Angustifolia.

If your lavender soap doesn’t smell strong enough, there are several ways around this, depending on what you’re more comfortable doing.

1. Add more lavender. Be bold! This is the most obvious solution, and probably the one you would try first. However, it doesn’t always work, and you need to be careful not to put more scent in your soap than the EU guidelines tell you to.

2. A better way to get your lavender to smell stronger is to let your melt and pour soap cool before adding the fragrance. Stir it to stop a skin forming on the top and wait until it’s reached about 37 or 38 degrees celsius, then add your lavender oil and pour straight into your soap mould. This takes practice because the soap will solidify very quickly, but adding the lavender at the lowest possible temperature will give you the best scent results.

3. The third way (if you want to cheat) is to use artificial lavender fragrance oil as well as your lavender essential oil. This will give your soap the fragrance you would expect from lavender soap while the essential oil sits in the background with its skin-loving properties. Obviously whether you would do this or not depends on how comfortable you are with artificial fragrance oils. I’m not the biggest fan of them, but if you find the right one they can be good.

How to safely use essential oils in home-made soap (infographic)

Essential oils can cause harm if used incorrectly because they are potent substances. Putting the essential oil on the skin neat (undiluted, or straight from the bottle) causes irritation and can leave your skin burnt. The oil is diluted in soap to a rate of about 3% (average) which makes it less likely to cause irritation although some sensitive souls are still allergic to some essential oils even at this low concentration.

Check out the infographic and follow these tips to use essential oils safely in home made soap:

1. Buy from a reputable seller

This is the most fundamental first step. It’s not always easy to spot a fake, especially because they’re being sold online where you can’t inspect the product.

A clear bottle is a dead giveaway as genuine oils degrade in sunlight so have to be stored in dark bottles (amber is most common).

The label or online listing should tell you the Latin name. There are many oils with the same common name. If you can’t see the Latin name anywhere in the product listing, there’s a chance the oil isn’t the one you expect it to be, which will ruin your blend at best, and at worst, could cause skin irritation because you might use the wrong quantity.

The listing should always tell you the country of origin. For example, “French lavender” might say “Product of Hungary” at the bottom of the page. This would make it apparent that it wasn’t genuine French lavender from France.

Of course, real malicious fakers and counterfeiters would not honestly write “Made in Kevin’s backyard out of olive oil and artificial lavender fragrance” so the most important thing to weigh up is whether you believe the website you’re shopping on is genuine, or in the case of Amazon, whether the seller is genuine or not. Product reviews can very easily be manipulated so don’t rely on them alone. Soapmaking groups online can help warn you against scams and recommend genuine, reputable suppliers.

2. Always follow the recommended quantities

The FDA and EU both have guidelines about the amount of any fragrance (including natural essential oils) you can use in cosmetics. Usually this is somewhere between 1-5% depending on the oil and its potential toxicity. It’s very easy to want to use more essential oil when your soap hasn’t turned out very strong smelling, but there are other ways to solve this problem. Check out my article 10 ways to get the fragrance to show up in your soap.

3. Do not overheat (above 50 degrees) and ideally keep under 40 degrees (102F).

Overheating oil causes it to release free radicals as the oil’s fatty acid chains break up. Free radicals are carcinogenic as they contribute to cell oxidation. Overheating an oil is the fastest way to change it from safe to dangerous.

When an oil gets too hot, it also loses its fragrance, which is another great reason to take care over the temperature.

4. Do not eat!

This should be self-explanatory but some people do try and eat (or drink) essential oils. Unless they have been certified for food use and sold as such, it’s best not to risk it, especially when it comes to children. Just because something came from a plant, that doesn’t make it safe. All the traditional poisons of Greek tragedies were plant-based.

Conclusion:

Essential oils can be safe in soaps if you take care and follow some simple guidelines. If you need to check any information e.g. chemical compounds present in your essential oil or the maximum concentration for use in various cosmetics and soap making, contact the seller for the product safety documentation (or download it from their website if they’ve made this easy. The Soap Kitchen makes this very easy, as an example of best practice).

Sources:

Turek, C and Stintzing, F (2013) Stability of Essential Oils: A Review https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12006

Bejar, E. (2019) Adulteration of Oregano Herb and Essential Oil https://www.researchgate.net/profile/Ezra_Bejar/publication/337113671_Adulteration_of_Oregano_Herb_and_Essential_Oil/links/5dc5cb74a6fdcc5750348535/Adulteration-of-Oregano-Herb-and-Essential-Oil.pdf

Check out my other articles about essential oils in soaps:

All about essential oils in melt and pour soap (and infographic)

How to get the essential oil scent to show up in soap

History of essential oils in soap

How to make soap: Everything you need to know to make soap even in a campervan.

Here’s a selection of my other articles about making home made cosmetics:

Vegan green tea shampoo bar recipe

Vegan hair conditioner bar recipe

One-ingredient avocado face mask recipe

Easy melt and pour breastmilk soap recipe

At-home DIY facial for new mamas!

10 ways to get essential oils to be more intense in your soap (melt and pour and cold process)

So you’re probably looking for how to get your essential oils to be more intense in your soap. You might be making cold process soap or melt and pour soap. Maybe you’ve made some homemade soap with pure essential oils and it didn’t come out with a strong scent, or perhaps you’re planning your first homemade soap making project and are hoping to execute a perfect first-time soapmaking recipe.

Here, I’m going to go through ten ways to get essential oils to be more intense in your soap. These methods for increasing the scent of your soaps are all based on principles of chemistry. Essential oils are volatile compounds which means they evaporate easily. That’s actually why we love them! They wouldn’t smell so good if they weren’t made exactly the way they are by nature.

Getting a stronger essential oil fragrance in soapmaking is one area where melt and pour soap really outshines cold process, and is one of the reasons I prefer melt and pour soap. Secretly, I think a lot of soapmakers prefer melt and pour, but it’s more profitable for them to write about cold process because it takes more skill to make it (so there’s more to write about).

Essential oils do really well in melt and pour soap. Cold process soap tends to eat the fragrance. But these are not hard and fast rules. It took me several attempts to get lavender essential oil to show up in my melt and pour soap.

If you look at my infographic on essential oils in soap, you’ll see the results I got when I tried a range of essential oils in melt and pour soap. Lavender oil was particularly problematic in melt and pour, and I’ve written a separate article on this.

1. Have you used the correct amount of your pure essential oil in your soap?

This is the easiest fix! All handmade essential oil soaps require different quantities of essential oils to get the perfect fragrance. Bramble Berry’s Soap Queen blog has a fragrance calculator that can help you out. You can find it here.

2. Add a clay as this can hold the fragrance in the soap.

Typically, this works to intensify the scent of essential oils in cold process soap, but I found it made a noticeable difference to increasing the scent of melt and pour soap too. French clay, kaolin and bentonite are all great choices, but some of them will colour your soap so be sure if you plan to sell your soap that the colour matches what you would expect for the scent (e.g. yellow-coloured lavender scented soap would probably be a bit confusing, but yellow-coloured lemon soap or grey lavender soap would make more sense). I prefer French clay and it produces interesting muted colour effects in transparent melt and pour soap base (you end up with a beautiful translucent glow).

3. Is your soap getting too hot?

For melt and pour, it’s easy to overheat the soap while you’re trying to get it to melt, particularly if you use a microwave (which is another good reason to make melt and pour soap without a microwave). For better results, don’t add the fragrance until the soap has cooled to about 37 or 38 degrees celsius. For cold process, pack your soap with ice packs to keep it cool. If you absolutely need your soap to go through gel phase (where it gets very hot), you might have to just accept that your soap won’t smell very strongly if you use essential oils.

4. Consider using a blend of essential oils instead of one individual oil in a soap recipe.

If you have a base note, a middle note and a top note, the fragrance is more likely to permeate the soap in a more nose-catching manner. An example would be lavender as the base note, chamomile as the middle note and lemon as the top note. There are other ways to blend essential oils (you can blend them by effect, e.g. for sleep you might use lavender, chamomile and valerian, or you can blend them by group, e.g. you might want an overall citrus scent incorporating lemon, ten-fold orange and citronella. Different scents have different volatility (evaporation point, which is when fragrance is unleashed from your soap), so a blend of oils will mean your soap has a nice scent regardless of the air temperature, pressure or humidity.

5. Consider using melt and pour instead of cold process, and avoid hot process entirely if you want your essential oils to smell more strongly in your homemade soap.

There is more going on during soapmaking than the soap getting hot. The process of oils turning into surfactants (cleansers) is called saponification, and this is a chemical reaction. The heat is just a byproduct.

6. Wrap your soaps in something as soon as they are able to be unmoulded.

The wrapping needs to be something that doesn’t let oxygen in. I’ve gone through twenty alternatives to plastic for wrapping soaps in this article.

7. Burn incense when you make soap.

Sounds crazy, right? But from a chemistry point of view it makes sense. Scent escapes because it goes from an area of high concentration to one of low concentration. If the air in your soapmaking place is already saturated with a smoky scent, such as an incense stick (not the scent of an oil diffuser) you can prevent scent loss in the same way smoked salmon’s flavour is sealed into the fish (only, you don’t want your soap to smell of smoke which is why you don’t want to go too far with this method). This is a balancing act because you must always follow ventilation safety when working with chemicals.

8. Let your soap harden (and cure) near a dehumidifier or a big bowl of rock salt.

An electric dehumidifier or a big bowl of rock salt will pull the moisture out of the air, which means the scent will have nothing to evaporate into, so it will remain in the soap for longer.

9. Add a sea salt such as Himalayan pink sea salt to your soap.

Himalayan pink sea salt looks beautiful in cosmetics, and especially when it’s embedded in bars of homemade soap. The pink crystals sparkle in bright lights giving your soap an ethereal quality.

Himalayan sea salt will work as a nice exfoliant as well as helping stop the scent escaping. Just don’t put big chunky pieces of salt into a facial soap or you will get redness.

10. Mix in some charcoal, or do a charcoal swirl.

The benefits of charcoal in soap include being fantastic for acne and great at purifying in warmer climates, as well as being a good additive to prevent your fragrance disappearing before you ever get to use your soap! However, charcoal is a black powder and it will change the colour of your soap. Doing a swirl with charcoal is another option, so part of the soap is more fragrant, which will improve the overall effect while still letting you use nice colours in the rest of the soap.

That’s my 10 ways to fix your soap if your essential oil fragrance is too faint or if your essential oil fragrance doesn’t last. Do you have any other ways? Share them in the comments!

History of using essential oils in soapmaking

Essential oils have been used for thousands of years. We have evidence dating back to Ancient China, India and Egypt of the use of fragranced oils (they’re mentioned in the Book of the Dead).

Frankincense was mentioned in the New Testament of the Bible and lipid residue analysis from archaeological sites shows plant oils were being used throughout history in a range of places such as Ancient Rome and Greece. The Romans used olive oil to get clean by covering their bodies with it then scraping it off with a special scraper. This was commonly done at bath houses.

There is a story that soap was first discovered by Roman women washing their clothes in the River Tiber below where the animals were sacrificed and the animal fat had somehow reacted with the clay in the river.

On the surface, this makes no sense because clay is not a source of sodium hydroxide (lye) and common wisdom says you cannot saponify without it. However, in reality, you could technically saponify with any aqueous alkaline (e.g. one with some water in it), and some types of soil are alkaline (these are almost always clay soils). I would want to do some experiments before being able to say one way or the other about whether this could really work or whether it’s just a nice fairytale about where soap came from.

The practice of putting oils into soap came later. In fact, while solid bars of soap seem old-fashioned to some people, they were only invented in Victorian times. Before this, people had a special jar of liquid gloop that was used for cleaning themselves, and they didn’t use it very often. So if you’re ever reading a Regency romance, when the author has a bath scene and the characters are using a bar of soap, you’ll know they haven’t done their research!

The Victorians were the originators of many of the unpleasant and outright dangerous chemicals that permeate our modern lives, and Victorian soap was no exception. The most popular type of soap was Carbolic Soap, aka Coal Tar Soap, which is about as unpleasant as it sounds.

It was made using the disinfectant carbolic acid, which is a carcinogenic and poisonous substance made from tar. It also has a distinctive ‘disinfectant’ scent that anyone who went to school in the 20th century would instantly recognize. Soap doesn’t need to contain any disinfectant to kill bacteria, however (we didn’t understand this back then — germ theory hadn’t been confirmed until Louis Pasteur’s work in 1863 and we didn’t have microscopes yet so couldn’t see them, either), something I will write more on in a separate article.

Soapmaking in Victorian Britain was an industry of mass-production using the cheap and disgusting byproducts of other industries (the standard ingredients were beef tallow, which is the fat that’s been removed from dead cows, carbolic acid, a byproduct of the tar industry, itself a byproduct of the coal mining industry, and sodium hydroxide, still used in soap today).

We tend to see the sodium hydroxide lye as the most dangerous and unpleasant aspect of soapmaking nowadays, but it’s the least awful of the three traditional soapmaking ingredients (fancy killing a cow and stringing it up to drain the fat, anyone? No?).

As a sidenote, tallow was also used for candle making. There’s a pub in York called the Guy Fawkes which I went in a few years ago and I couldn’t breathe while I was in there because it was lit by hundreds of candles. It was really beautiful and atmospheric but the smell of evaporated beef tallow was really sickening because I was vegan at the time.

It’s not clear when the first essential oils were used in soap, although it was only in the twentieth century that essential oil soaps became mass-produced as the New Age revolution of the sixties rejected the artificial byproducts of capitalism that were making people sick and destroying the landscape, and they started to question the way things were. Thanks, hippies!  I love that there’s another connection between vanlife and soapmaking in the history of the use of essential oils in soap.