How to calculate the hot process superfat
In my previous post I discussed an important difference between superfat and lye discount. You might want to read it first, as I explain there why in hot process (HP) and only in hot process, the calculation of the superfat should be based on the saponification values and not on the percentage of oils.
I introduced there a formula on how to calculate the % of superfat given a recipe in the hot process method. In this post I show the other problem – How to calculate the amount of oil in order to get the desired % of the hot process superfat.
First, I repeat the first calculation:
How to calculate the HP superfat given the amount of oils added at the end
To summarize, it is 1B/A, where
A – is the amount of lye needed to saponify all the oils in the recipe (including those added after the soap is finished), at 0% lye discount
B – is the lye needed to saponify only the oils in the basic recipe (without superfat oils)
But what if I do want to calculate it viceversa? I do not want to find a superfat % given the amount of my superfat oil, but I want to find how much of the oil should I add in order to get a certain superfat %!
How to calculate the amount of oil in order to get the desired % of superfat in HP
I will use a basic recipe from a post on talksoapforum, where this question was asked by Heavensgrace.
Basic recipe:
135 g (4.8 oz) palm oil
135 g (4.8 oz) coconut oil
317 g (11.2 oz) olive oil
lye needed to saponify at 0% superfat is 87g (3.078 oz)
We want to superfat this basic recipe with shea butter and castor oil at 10%.
Question is: How much of shea butter and castor oil we need to add in order to obtain 10% superfat?
If we want a 10% superfat, we are adding oils representing 10% of the lye needed to saponify all the oils (basic recipe + superfat oils). This means the basic recipe represents a fraction fully saponified by 90% of the lye and the 100% lye needed for the recipe is calculated as
87/0.9 = 96.7g (or 3.078/0.9=3.42 oz) – This is the amount of lye needed to saponify 100% of oils.
Therefore we need the quantity of oils that would be saponified by 96.7g–87g = 9.67g (or 3.423.078 = 0.342 oz) of lye (10% of the whole lye amount). Both castor oil and shea butter have both 0.128 SAP.
The quantity of oil to get the 10% superfat would be 0.128 SAP * x = 9.67 oz => 75.5 g
(or 0.128 SAP * x = 0.342 oz => 2.67 oz) of shea butter, or 75.5g (or 2.67 oz) of castor oil, or basically any combination of the two as soon as they add up to 75.5g (or 2.67 oz) (we can do this, because they have the same saponification value)
So, to make a formula out of it:
B – is the lye needed to saponify at 0% the basic recipe (in your case it is 3.078 oz)
C – is the superfat % you wish (10%, please use 0.1)
SAP – is the saponification value of the superfat oil you want to add (0.128 for castor oil)
D – is the amount of the superfat oil we need to add to achieve C
E – is the amount of lye needed to saponify all the oils (the basic recipe + superfat oils) at 0% (in other words if superfat oil was part of the recipe and you did not superfat at all)
E = B/(1C)
D = (EB)/SAP
(in our example
E = 3.078/(10.1) = 3.078/0.9 = 3.42 oz
D = (3.423.078)/0.128 = 2.67 oz
)
This entry was posted by evik on April 15, 2013 at 11:20, and is filed under for beginners, soapmaking, soapmaking basics. Follow any responses to this post through RSS 2.0.You can leave a response or trackback from your own site.


#3 written by PeterV 3 years ago
What about if you want to superfat with two oils in combination that have different SAP values, like Cocoa Butter and Shea butter? I have a recipe that would call for 5.4 oz of Cocoa butter to get a 10% superfat, or 5.8 oz of Shea butter to get 10%. I’d like to use both to superfat. Would it be correct to divide both amounts in half (50% plus 50%, or 2.7 oz of Cocoa butter plus 2.9 oz of Shea butter) to achieve the proper amounts of each to add to arrive at the 10% superfat figure? Maybe this is obvious, but it isn’t to me.
Your website is a great help to me, by the way!

#4 written by evik 3 years ago
Hi Peter,
yes, your assumption is correct! As soon as you know how much you need for each oil, than you can simply combine them.
O1 – amount of one oil to get 10% superfat
O2 – amount of second oil to get 10% superfatIf 50:50, then 0.5*O1 + 0.5*O2
if 20:80, then 0.2*O1 + 0.8*O2
…etcworks for more oils, of course, the very same way.


#6 written by Tasha 2 years ago

#7 written by Christina 2 years ago
I appreciate your explanation about this. But I have to pose a question. I actually am a math person, have always done very well, so I did not have a hard time understanding your explanation. After reading everything, and rechecking what superfatting actually IS, aren’t you really just trying NOT to saponify 10% of your oils if you are looking for a superfat of 10%? If that is the case, then wouldn’t it be much easier to look for the amount of oils that would make 10% of your total recipe, and then use enough lye to fully saponify the other 90% of oils to a 0% SF? So, in other words, in your example, you would be looking to see how much oil would make the original 20.8oz 90% of the recipe. 20.8oz/0.9=23.11oz making your total oils 23.11oz, and therefore the other 10% would be 23.11oz20.8oz= 3.3oz And then it would not matter what kind of oil you use, especially because none of the superfatting oils are going to be saponified anyway, since they are added after the cook.

#8 written by evik 2 years ago
Hi Christina, thank you for your comment. I know where your confusion comes from. The problem is – and I think I have to state it maybe in the beginning of the post – that superfat means % of unsaponified fatty acids, not the % of unsaponified oil weight.
Each oil has different saponification value – this is due to the quantity of fatty acids in this oil. For instance – 100g of coconut oil contains more fatty acids than 100g of olive oil. That is why it needs more NaOH to saponify.
Now we don’t really care about this in oneoil recipes, nor in the cold process recipes with mixed oils. Why? Because the oils are mixed and we calculate SAP for the mixture of oils. There if you discount 5%, you discount 5% of one oil, or of a mixture of oils, where fatty acids are already mixed well and so 5% of the unsaponified fraction has the same amount of fatty acids as each of the nineteen 5% portions of saponified fraction. I hope I did not loose you here.
So basically, in cold process, it is exactly as you say. It is also true in HP if you would just mix your oils and then took 5% out and added it after the saponification is complete.
However, the problem starts in hot process when you are trying to add a single oil with a different fatty acid profile than the recipe. If coconut oil has more fatty acids than olive oil, this means that let’s say (now I invent numbers) 1g of coconut oil contains 100 fatty acids, while 1g of olive oil contains 50 fatty acids. If try to add 5g of coconut oil to soap made from 95g of olive oil, you are basically adding 500 fatty acids to 50*95 = 4750 fatty acids. Then it is a simple math: 500/c(4750+500) = 9.5% …this is not 5%, right?



#11 written by Tanisha 2 years ago
Hi Evik – I have found your information to be very helpful to me. To tack on to Peter’s question and your answer above, I have a math calculation I want to make sure is correct.
I want 10% superfatting with Cocoa Butter and Shea Butter mixed together at an equal percentage.
The SAP value of Cocoa Butter is .126
The SAP value of Shea Butter is .131
Since they have different SAP values, would I use your last formula: D=(EB)/SAP for each SAP value separately? 

#13 written by evik 2 years ago
Hi Jacqueline, sorry for my late reply. I am not sure when are you adding the shea butter and avocado oil, but normally, if you HP your basic recipe with 0% lye discount (which is what you should do when superfatting), of course, it can zap before you add your superfatting oils, since there are small differences in superfat.
However, looking at your recipe, it rather seems you have too little lye. You need 3.751 oz of lye to fully saponify your coconut+castor+olive oil.
Adding 1.48oz of shea butter and 1.43 oz of avocado oil (which need 0.379 oz NaOH) then makes it 9.2% superfat.
If, however, you only used 3.44 oz, then you have 0.311oz NaOH less then you should, which makes it overall 0.379+0.311=0.69oz of NaOH that you did not add, which makes it 16.7% of superfat…How did the soap turn out finally?



#15 written by Donna 2 years ago
I’m sorry, but I came here from a post on the hot process facebook page. I’ve made a few batches of hp soap using the soap calc. I learned from Irena on the teach soap forum (which is all cp) that the lye would take whatever fat it wanted/needed and what was left over would end up being the super fat. So I just calculated the oils at soap calc at 10%, mixed it all together that way and cooked it. How is putting the oils in after the cook different?
I’m HORRIBLE at math, and the above post is HORRIBLY confusing for me. I read it 3 times and still don’t understand it.

#16 written by evik 2 years ago
Hi Donna,
as you correctly know, the lye will first react with some oils, because of their composition of fatty acids. From this point of view, there is no reason to add oils we do not wish to saponify “at trace”.
However, people still wish to add oils and say – these are those that make the superfat – these did not saponify. This is, however, for the above reasons, possible only once the saponification finished. And this means you can only superfat this way in at the end of HP.
If you add a certain amount of hemp oil at the end of the HP, this will not saponify and you can say “this soap is superfatted with hemp oil”.I am not sure if you read my post on the difference between superfat and lye discount – this might help you to understand this post and the calculations within. In any case, I believe you will understand once you realize that superfat is not calculated based on “grams of oils”, but based on saponification values of oils. If you understand what SAP stands for and why it is needed to calculate the right amount of lye, you will understand why it shall be used for calculation of the superfat.
I was already thinking to adjust the post to make this more clear, though, since noone really reads other posts first :).Let me know, if it is more comprehensible, I shall rewrite the post soon…


#18 written by Dale 1 year ago
I read and reread your article, but I never saw where you defined what “E” represents. I did figure it out by going back and looking for the numbers that E resulted in. Just to be sure; is E not the total lye required to saponify ALL the oils, including Superfat? If I missed this definition in your article, I sincerely apologize.


#22 written by evik 1 year ago


#23 written by Veronika 1 year ago
Hey, I am happy I found this post. Have been doind CP soap until now and want to make HP ať last and still I didnt know how to calculate – and I know found this! Cool! But… It’s too complicazed for mě also because ounces are so hard to jmagine ;))
Can you please make me an example of a simple formula using 1000 g of oils?Is it correct, what I’ve been told elsewhere, that if I want to make lets’s say 5% superfat for a 1000 g batch, it would be 50 g of oils to superfat… So I would run a recipe though soap calc with 950 g of the oils and 0 % superfst and then add 50 g after gel phase?
I am not really sure about this, would be really helpful if you could advise :)) thanks!
#24 written by evik 1 year ago
Hi Veronika – I added grams to the calculation example. The formula at the end is universal – doesn’t matter if you use ounces or grams or kilograms, as soon as all your measures are the same. The statement on how to calculate superfat is correct, if you mix the oils and then spoon out 50grams of oils and add them once soap finished by HP. If you wish to superfat with a particular oil, you need to think about how much of fatty acids it contains in a gram. In other words – you calculate superfat based on saponification values, not based on grams of oils. For more info, see this post: http://curioussoapmaker.com/superfatvslyediscount.html Hope this helps!
Also, it seems you are czech, you might be interested in my slovak blog moderna.alchymistka.eu.


#26 written by Mai 1 year ago

#29 written by haak 1 year ago
Or:
Go to the Brambleberry Lye calculator and enter %, not oz. Enter total oil weight, in my case 36oz. Enter percentages of all fats and oils used in recipe including superfating oil, which is 5% as I want to superfat to 5% (if you want to superfat to 7%, enter 7%). If you don’t know your percentages see note below. My superfating oil is Almond oil. Press calculate at 0% superfating rate. Write down the Lye weight in oz, and the weight of the superfating oil (almond oil in my case). This is the Lye weight necessary to Saponify all your oils and fats including your superfating oil. Go to the Lye calculator and press start over. Enter the weight of the superfating oil into the appropriate space and press calculate at 0% superfating rate. Write down the Lye weight. This is the amount of Lye necessary to Saponify just your superfating oil. Subtract the superfating oil Lye amount from the All oils and fats Lye amount. Use the resulting amount of Lye in the recipe at the start of the cooking process without the superfating oil added. After you cook (saponify) your batch, add your superfating oil (the weight of which you wrote down).
Note:
Using the Lye calculator set on oz, enter your oil and fats without superfating oil into appropriate spots. Press calculate at 0% (at this point it does not matter what the % is). The resulting page will display the percentages of your oils and fats and total oil weight. Print this page. Press Start over, select %, not oz and enter the total oil and fats weight that you copied from your printed sheet. Now enter all your oil percentages into appropriate spots without the superfating oil. Note; right above the “Oils” heading is a % window, it tells you the total % entered. Without your superfating oils it should read 100%. Now you have to make room for 5% superfating oil (if you are superfating to 5%) Enter 5% oil or fat of your choice and click your mouse to update page data. Your total percentage should now read 105%. Take away a total of 5% from your other oils to bring the total to 100%. Press calculate at 0% superfating rate. The resulting page will show the oil weights including your superfating oil weight. 
#31 written by Lav 11 months ago
Great post/article. Loved it. This was exactly what I was looking for and I’ve been studying this for some time now. A definite bookmark.
Just to clarify, being a noob and all, “basic recipe” = oils – the superfatting oils?
Once the calculations are completed, do we use the “B” or the “E” amount of lye when executing the recipe?
Thank you for your work and contribution.

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Great tutorial! I’ve used this calculation ever since and never had a bad batch of HP soap!