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!

Soapmaking: What is a water discount?

A water discount is a reduction in the amount of water needed to dissolve sodium hydroxide lye. When you use a water discount, the soap will harden faster because there is less water in its batter (the mixture that eventually becomes soap). You only use a water discount for cold process or hot process soaps that use lye. You don’t need a water discount for melt and pour soap because the oils are already saponified and the lye has been used up before you ever get the melt and pour container!

Advantages of a water discount:

  • Your soap will cure faster
  • Your soap will be harder (ideal for Castile soap)
  • The soap can be taken out of the mold more easily
  • The mold will be easier to clean (less residue = less cleaning of the little corners of your molds is required – a constant problem I’ve had with homemade cosmetics, especially my all-natural conditioner bar).
  • A water discount helps balance the recipe if you’re adding other ingredients that contain water such as if you are using milk (including breastmilk) or if you’ve mixed mica powder with water rather than alcohol before adding it to your soap.
  • If you want to force a strong gel phase for a specific soap design, a water discount is a great addition to the other things you can do such as using heat pads around your soap while it’s curing.

Disadvantages of a water discount:

  • Your soap batter will thicken (solidify) faster, making it harder to work with. If you’re doing a color effect such as a swirl, you will want your batter to reach trace (ideal thickness) then to solidify slowly, to give you time to make your desired effect.
  • It can also effect your colors by messing with the heat of the soap. The reaction between lye and oils (saponification) is an exothermic reaction — it gives out heat. And if it heats up too much, it will affect what the soap looks like. If you want to avoid gel phase (e.g. when making cold process breastmilk soap, you do NOT want it to get too hot or the milk will spoil before the soap is done), don’t water discount more than you need to for the extra liquid in the milk.

To calculate a water discount, you use a percentage:

The usual amount of water to lye is 70% water to 30% lye. That means you use 70ml of water for every 30g of lye.

Discounting the water by 10%, you would have 63ml of water to 30g of lye.

Discounting the water by 20%, you would have 56ml of water to 30g of lye (this is a heavy water discount).

You also need to factor in whether your recipe requires a superfat (leftover oil for more nourishing soap bars). In this case, you usually wouldn’t discount your water.

Stuck? The very best resource on calculating the amount of oils, water and lye for your recipe is the Brambleberry Lye Calculator (it also calculates fragrance, but beware in the EU some of the fragrance results are higher than permitted under EU law if you’re selling your soaps). This tool is phenomenal!

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.