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!

Vegan green tea hair shampoo bar recipe

My love affair for all things green tea began long before I ever moved to East Asia. Being in Japan last year really cemented it.

The rumors about Japan are true. They use matcha green tea for everything. In our hotel, the shampoo and conditioner were green tea. And they were phenomenal.

So since lockdown, when soap and other cosmetics suddenly vanished, I decided to start making my own cosmetics. I had planned to make a melt-and-pour shampoo bar before anything else, but I ended up making soaps successfully, first, and getting product safety tests done on my essential oil soaps. At the same time, my shampoo bars were not going so well.

I couldn’t understand it. Both my soaps and the shampoo bars were made using the correct bases (don’t use soap base for shampoo bars! I know a lot of bloggers say you can do it with soap base, but if you care about your hair, you need to use proper shampoo base) but my shampoo bars weren’t mixing properly and when I tested them on my hair, they left residue. Eeek!

Eventually, I found out where I was going wrong. The rubbing alcohol in this recipe is essential. Do not skip that step.

You will need (makes one 100 gram bar; scale up for more than one):

  • A glass jug
  • A saucepan of boiling water on a stove
  • A spoon
  • 85 grams Stephenson’s Solid Shampoo Base (this doesn’t seem to be available to buy on US Amazon but you can get it shipped to the US from the link above which is UK Amazon)
  • 1/4 tsp Green tea powder
  • 1 tsp Rubbing alcohol (I’ve linked to Amazon there in case you can’t get out to a store, but you can get cheap rubbing alcohol in the Dollar Tree so don’t spend more than you have to).
  • 5 grams Avocado oil (substitute with another oil such as olive oil, jojoba or almond oil if you don’t have this)

    If you’re in the UK/Ireland you can get your green tea, rubbing alcohol and avocado oil on these links, instead.

How to make vegan green tea melt and pour shampoo bar:

  1. Cut the melt and pour shampoo base into small squares and put it into the jug.
  2. Place the jug inside the pan of boiling water (alternatively, use a microwave to melt the base).
  3. Remove when the shampoo base has melted.
  4. In a small cup, mix the green tea powder with the alcohol.
  5. Once this is mixed, add it to the shampoo base.
  6. Add the avocado oil.
  7. Mix well.
  8. Pour into your soap mould. Leave to harden for about an hour and a half, then wrap.

I am so happy with this recipe (finally)! Let me know what you think in the comments! If you have a microwave, you can melt the melt and pour shampoo base in your microwave, checking every 30 seconds to be sure not to scald it!

Want to know more about how to make your own cosmetics? Check out my complete guide to soap making.

Vegan hair conditioner bar recipe that you can even make in a campervan!

I searched and searched the WHOLE DAMN INTERNET and none of it had a recipe like this. I wanted a recipe using natural, vegan ingredients, so I could make my own conditioner bars. I also wanted something that didn’t require expensive or bulky equipment to make it.

I needed this recipe to make a bar, not a liquid, because I travel a lot and I have super dry curly hair, and I am very fed up of not being able to take conditioner on a plane unless it’s in my checked baggage or in a very tiny bottle.

When I didn’t find a vegan hair conditioner bar recipe for travel, I made my own.

This bar is super-nourishing for very dry hair, you really don’t need much of it. I like to use it by working it into the ends first, while my hair is wet, then moving up slowly until I get to my ears. Lastly, I put the rest onto my hair from my parting downwards in one or two swift strokes.

If you accidentally use too much, get a bit of your shampoo bar and rub it between your hands then wipe the lather onto your hair where there’s too much conditioner.

This conditioner is a little bit soft, I’ve played around with the recipe and every time I’ve tried to harden it, it just goes oilier but not harder. So I find the original bar cracks into three or four pieces after a few uses, but after that it seems pretty stable.

If you’re a fan of using a bit of coconut oil to moisturize your hair, you will LOVE this recipe as it incorporates coconut oil but makes a solid bar for travelling with!

You will need:

  • A glass jug
  • A spoon for mixing
  • A soap mould
  • 40g shea butter
  • 30g olive wax
  • 20g cocoa butter
  • 20g coconut oil
  • 10ml rice bran oil
  • 10ml avocado oil
  • 30 drops lavender oil (or other essential oil of your choice)

Method (no microwave… scroll for microwave method)

  1. In a saucepan, boil some water and place your glass jug in it.
  2. Add the cocoa butter and olive wax as these take the most heat to melt.
  3. When they have melted, add the rest of the ingredients except the lavender oil.
  4. Once the whole lot has melted, remove jug from saucepan, add lavender oil and mix well.
  5. Pour the mixture into your soap mould and leave it to harden. This takes about 2-3 hours.
  6. Pop it out of the mould. Wrap to keep moisture out and it’s ready to use!

Microwave method:

  1. Put the cocoa butter and olive wax in the microwave and heat in 30-second bursts until they have melted.
  2. Add the rest of the ingredients except the lavender oil and heat in 20-second bursts until everything has melted.
  3. Add the lavender, pour into a mould and leave to harden for 2-3 hours.
  4. Pop out of mold. Wrap. Enjoy.

So there you have it, a 100% vegan conditioner bar recipe that requires nothing complicated or weird, no dodgy chemicals and you can even make it in a campervan. Let me know if you’ve used it!

If you want to learn more about making cosmetics, you might like my really long and comprehensive article on how to make soap!