Keep Your Superfat Up when Using Orange Juice

[Seifenblasen]

I have seen glancing through a lot of discussions on using citrus (juices) in soap and some extremely low superfat numbers used. Since I am sitting at the airport doing nothing, I did some quick calculations, mainly for my own entertainment, but thought I would share the results. If it sounds like mumbo jumbo to you, or if you don't believe anything I say, that's OK, won't hurt my feelings. For those who care, I must admit I am being very sloppy with significant figures.

The conclusion is you really need not adjust your superfat when using orange juice as it changes about only 1%. It is understood that the acidity in oranges (or any other fruits) varies, due to ripeness, types, etc., but even a very tart orange juice is not going to consume enough NaOH to change the resulting superfat more than 1 or 2%.


Assumptions:
1. Specific gravity of orange juice (OJ): 1.15
2. Two acids of concern in OJ: citric acid and ascorbic acid
3. Citric acid concentration in OJ: 36 – 427 mg/fluid oz., using an average of 231.5 mg/fluid oz., equals to 7.27 mg/ml (http://www.cord.edu/dept/chemistry/CCJAC/2012_Vol_3/2012_3_57.pdf)
4. Ascorbic acid concentration in OJ: 97 mg/8 fluid oz, equals to 0.40 mg/ml (http://nutrition.about.com/od/thera...-Servings-For-A-Days-Worth-Of-Vitamin-C_2.htm)
5. Assume complete dissociation in water (I did not bother to look up the K values).

Known Facts:
1. Reaction between NaOH and citric acid:
C3H5O (COOH)3 + 3NaOH = 3H2O + C3H5O (COO)3Na3
2. Reaction between NaOH and ascorbic acid:
C6H8O6 + NaOH = H2O + C6H7O6Na
3. Molecular weight of citric acid: 192.124 g/mol
4. Molecular weight of ascorbic acid: 176.12 g/mol
5. Molecular weight of NaOH: 33.997 g/mol


If we were to make a simple soap using 1000 g of coconut oil with full water content (38% of oil = 380 g, or 380 ml), Soap Calc generated the following amounts for NaOH based on the different levels of superfatting:

183.24g NaOH – 0%
174.08g NaOH – 5%
172.25g NaOH – 6%

Based on the above equations, 1 mol of citric acid reacts with 3 mols of NaOH, and 1 mol of ascorbic acid reacts with 1 mol of NaOH.

If we replace 100% of the 380 ml water with OJ, the amounts of acids we have are:

Citric acid: 380 ml x 7.72 mg/ml = 2933.60 mg = 2.9336 g
2.9336 g / (192.124 g/mol) = 0.0153 mol
Ascorbic acid: 380 ml x 0.40 mg/ml = 152.00 mg = 0.1520 g
0.1520 g / (176.12 g/mol) = 0.0009 mol

The amount of NaOH consumed by the acids in 380 g OJ is:

3 x 0.0153 mol (amount consumed by citric acid) + 0.0009 mol (amount consumed by ascorbic acid)
= 0.0468 mol

Since the molecular weight of NaOH is 33.997 g/mol,
33.997 g/mol x 0.0468 mol = 1.5911 g

So if you replace the 100% of the water with OJ, and superfat at 5% (using 174.08 g NaOH), your NaOH “loss” due to reaction to the acids in OJ is only 1.5911 g, which would not even result in a 6% superfat (as 6% superfat would mean using 172.25 g NaOH).

174.08 g – 1.5911 g = 172.48 g


You can do the same calculation for lemon juice, lime juice, etc. Just keep in mind although those fruits are slightly more acidic than orange, it is unlikely you will replace the all the water with lemon/lime juice. So the effect is, again, quite negligible.

 

[Badger]

Thank you for your work with this, but just looking at it makes my brain hurt. I can follow most of it at least

 

[Dorado]

Thank you very much for sharing.
It sounds very reasonable, it is a just a bit mumbo jumbo for me, but I def understand, (and I trust your conclusion)
Since my garden is loaded with overriped oranges, I will try to up my SF from 2% to 6%, when I make the next orange batch
Have a nice flight (that is if you are flying I mean)

 

[green soap]

Thank you for sharing your calculations, it makes a lot of sense for oranges and tangerines.

The % acidity for an average real lemons (as from my tree, not the real lemon product) is roughly three times that of an average orange. Following your example this puts your amount of NaOH consumed by citric acid at about 4.8 g - so this would change a couple of % ponts in the superfat. Still not a really big deal, unless your SF is already high. I did not look up how much more ascorbic acid, so this is a rough estimate only.

Grapefruits are somewhere in between. Meyers lemons (hybrid between orange and lemon) are in between as well.

We should make a table of SF % increase with 100% full water substitution for the different citrus! but I am not at the airport and have several coconuts to grate. Have a good flight!

 

[Seifenblasen]

Thank you all! I am safely back on terra firma.

@ Dorado, since your oranges are very ripe, I would assume even replacing all the water with juice, it will only up your superfat 1 to 1.5%.

@ Green Soap, found another table (go to table 1 of the article) with info for lemon and lime juices! You are absolutely right that their citric acid concentration can be several times (actually up to 5 times, in some instances) higher than orange juice, but I don't know too many people replacing 100% of the water with lemon/lime juice ...

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2637791/

 

[Lindy]

Seifenblausen thank you for sharing your thoughts however it has already been demonstrated by Soaping 101 if you use your usual superfat (I believe she uses 5%) and 100% lemon juice as your water you end up with mush. Citric Acid will do the same thing to soap if you add too much.

http://youtu.be/wFOdi989-aU

 

[Seifenblasen]

I hate to disappoint you, Lindy, the video has nothing to do with what I wrote. You are comparing apples and oranges, or in this case, lemons and oranges.

The original calculation was made on orange juice, and juice alone - no pulp, rind, pith, or any of those junk. Secondly, if you read the conversation between Green Soap and myself, I agree with her that lemon juice and lime juice can have up to five times the concentration of citric acid, compared to orange juice. I have no idea what crazy thoughts compel the person who made that video to replace all water with lemon juice and junk, but most sensible soap makers, like Tilly, uses only the juice of one lime to replace a portion of the water.

And why would I add citric acid to soap? :Kitten Love: It reacts with NaOH and becomes sodium citrate, which is good in creating a smooth mac and cheese, but has no benefit in soap.

Anyway, it's a free world. People can post anything on YouTube, write a blog on making soap without lye, and there is not shortage of misleading information floating around (including me faulty calculations, I guess :twisted. Most people, however, are smart enough to draw their own conclusion.

 

[AngelMomma]

Soaping101 does videos like that as a demonstration to show the results. Like for newbies or for people who haven't studied up on making a lemon soap. For instance if I were going to make a lemon soap and was going to replace the water with juice from my lemons, I could draw the conclusion(after watching her experiment video) that I should only replace part of the water with the citrus juice.

It would save me from wasting a whole batch of soap, or having to rebatch.

 

[Lindy]

True, but it also lets you know that if you are going to use 100% for the water that you need to increase your lye to offset the acid in the citrus fruit. It is helpful to consider which are them most acidic which allows you to adjust accordingly, but regardless you are going to need to adjust to some extent. Now I'm not a scientist, but I do believe in logic....

 

[Dorado]

Thank you Seifeblasen, I used 100% orange juice alone - no water, pulp, rind or pith, in the orangesoap I made last weekend
No problem at all.
And I will try the exact same receipe again, only with higher SF, no colour or FO, starting with separation of orange juice today.

 

[lsg]

If you have watched very many YouTube videos, the lady on Soaping 101 is hailed as very knowledgeable. A pleasant tone contributes much to the goodwill of the forum. Sarcasm never accomplishes anything except bad feelings.

 

[Seifenblasen]

In any science experiment, it is customary to do the calculations first before jumping in the lab and start throwing chemicals around. The references and calculations showed that with ripe orange juice, it will only affect the resulting superfat 1 to 2%. As said in the original post, you don't have to believe any of that and you are free to run your own calculations.

My question back to you all who feel the need to drastically drop the superfat is: by how many percent? And how do you come up with that number? And is it a one size fit all - regardless it is lemon, lime, grapefruit, or orange juice, and regardless how much you use?

 

[AngelMomma]

True, but it also lets you know that if you are going to use 100% for the water that you need to increase your lye to offset the acid in the citrus fruit. It is helpful to consider which are them most acidic which allows you to adjust accordingly, but regardless you are going to need to adjust to some extent. Now I'm not a scientist, but I do believe in logic....

I have 3 citrus trees that I am hoping do well this year. I haven't ever made a citrus soap and would like to use my own fruit. I have read some and watched some videos. And of course I do know that citrus fruits have a varying amount of acid levels. I chose one (improved myer lemon) for the fact that its a lower acid level. They are AWESOME! So I am considering when the time comes later this year (Or if I get a good deal on fruit earlier) dropping the superfat level to 1% or 2% which essentially increases the concentration of lye. It will be a fun sciency experiment. :smile:

 

[AngelMomma]

What would be an accurate way to test any given citrus juice to get an idea of what the acid level is? For example I sometimes buy oranges and lemons. But I also have the variagated lemon, Improved meyer lemon and Blood orange trees. I would be interesting to compare the levels of those, one to another.

 

[Lindy]

Steifenblausen, since you have the scientific background, perhaps you could do us all a favour and create a chart that a layman/woman can understand (that would be one who is not a scientist) as to how much the Super Fat should be adjusted for each citrus with the assumption that the person is going to use 100% juice in order to maintain the SF they are already using. I think that would be extremely helpful to the entire forum.

Thank you in advance.

 

[green soap]

type of citrus juice ------ increase in superfat (in %) upon 100% water sub

oranges and tangerines ----- 0.5 - 1.2

grapefruits and meyers lemons ----- 1.5 - 2.5

lemons and limes ----- 2.5 - 5

minneolas??????? (got 2 large trees)

The numbers go like estimated above, but it depends so much on the variety. Seifenblasen, please feel free to correct it.

For a more accurate estimate, find out the acid % in your variety and then plug the value in Seifenblasen sample calculation above.

A Boerrs lime is going to be much different than a Key lime, and Meyers are not true lemons but hybrids with orange, so they acidity level is much lower (lower drop in superfat). Then there are minneolas, which are a grapefruit-tangerine hybrid, and they are sweet but also very acidic. I grow all of these, I wish I could set up inexpensive titration system. Chem glassware is spendy though.

 

[Seifenblasen]

Thank you, Green Soap! I am amazed at the variety of hybrid citrus you have!

Anyway, I worked up a rough spreadsheet where you can just plug in the amount of juice you use in ml, and it will tell you the amount of lye consumed by the acids. So you can play with the numbers based on the actual amount and type of juice you use.

A few warnings:
1. The number for orange juice is slightly different than the original calculation as I switched to a different source. Originally I used a paper from a university's chemistry department. For this spreadsheet, I used a table from a medical paper.
2. Since I cannot find much info on Meyer lemons, and since they are a hybrid between lemon and orange, I used a number half-way between lemon and orange.
3. As mentioned in the original calculation, the acid content of fruits varies a great deal. Short of setting up a titration system as suggested by Green Soap, these are just reference numbers and may not be an exact representation of the juice you have on hand. However, I think it will help you figure out the ballpark figure before experimenting.

Now the question for Lindy is, how do I send you a spreadsheet so that it could work as a tool? A screenshot is attached, and as you can see, it is pretty simple - just put in the amount of juice in the pink area, and the amount of lye consumed will show up in the orange area. In this case, if I use 200 ml of lime juice, the amount of lye "used up" by the juice will be between 4.50 and 5.23 g.

 

[Lindy]

Thank you both. Seifenblausen is it possible to get a download of your spreadsheet? I would love to have that for reference purposes.... I want to make more citrus soaps and the information is helpful....

 

[Dorado]

Seifenblasen - I think I like you very much
If you ever visit Spain or Denmark, I will have coffee and homemade cake ready.
And a good orangesoap to wash your fingers.

 

[Seifenblasen]

Thank you, Dorado! And if you happen to be in the US, do let me know. And I mean it.

Lindy, I would be more than happy to share the spreadsheet, and interested in knowing how well/poorly it works, and will tweak it to add more fruits and/or adjust the numbers used. Unfortunately I cannot make any soap in the near future as I have been/am traveling a lot for work. Don't think the hotels would appreciate me mixing lye in the bathroom ... :twisted:

Tried uploading the spreadsheet but SMF would not take it. Could I email it to you and perhaps you could find a way to share with others in the forum? Thanks!