Sodium citrate from baking soda and citric acid

[galaxyMLP]

Sodium citrate acts as a chelator for the metals found in hard water. It reduces the amount of soap scum that forms when added in an amount of 1-3% of the amount in a batch.

I have very hard water where I live so I wanted to try this.

Another great chelator out there is EDTA. However, with all of the "natural" junkies out there, sodium citrate "sounds" better (and, in my opinion, can be cheaper in the long run [thats really why I like it])

ETA:
Soap scum is formed when insoluble salts of fatty acids are created. Sodium and potassium salts of fatty acids (solid and liquid soap respectively) are soluble in water. However, calcium, magnesium and other metal salts of fatty acids are not soluble in water. This is what causes soap scum or tub ring.

ETA2: Chelators are basically chemicals that have available sites on them that can bind to other ions. They effectively take up the "reacting power" or "binding power" of many different ions (for example calcium in this case)

 

[DeeAnna]

The purpose of citrate (or tetrasodium EDTA) is to chelate (bind up) metals. Adding a chelator (aka chelant) to your soap batter will reduce the chance that your soap will become rancid (get DOS) as time passes due to metallic impurities.

A chelator in your soap also reduces the amount of soap scum that occurs when lye soap reacts with hard water minerals while you shower or bathe. Soap scum can make your skin sticky, itchy, and sometimes irritated and can also reduce the lather your soap makes.

CITRIC ACID in Soap
Typical dosage: 10 g citric acid for every 1,000 g oils (1% ppo). Range 0.1% to 3%.
Citric acid reacts with lye, so you MUST add additional lye (NaOH or KOH) needed for the citric-lye reaction. If you do not add this extra lye, your superfat may be higher than you want it to be in your finished soap. In bar soap, this extra superfat may reduce lather and may make the bar softer. In liquid soap, this may cause fats to separate out and float on your diluted soap.

Citric acid and Sodium hydroxide (NaOH) make Sodium citrate in soap
10 g citric acid neutralizes 6.24 g NaOH

Citric acid and Potassium hydroxide (KOH) make Potassium citrate in soap
10 g citric acid neutralizes 8.42 g KOH

Stir the citric acid into the water you will use to make your lye solution. Add the lye to the water and proceed with your recipe as usual.

SODIUM CITRATE or POTASSIUM CITRATE in soap
If dosage rate for citric acid is 1%, the equivalent dosage for sodium citrate is 1.3%
If dosage rate for citric acid is 1%, the equivalent dosage for potassium citrate is 1.6%

Do NOT add additional lye if you are using potassium or sodium citrate. Extra lye is only needed if you are using citric acid.

Stir the citrate into the water you will use to make your lye solution. Add the lye to the water and proceed with your recipe as usual.

EDTA in Soap
EDTA comes as a powder. Typical dosage is 0.5% of EDTA powder based on batch total weight (fat + lye + water).

You can dissolve the powder directly in your lye water, but most of us make a water and EDTA solution and add the solution to the lye water or oils. The solution most of us use is 39% EDTA dissolved in distilled water (39 g EDTA + enough water to = 100 g of solution). Since you need so very little EDTA, it is easier to measure as a solution rather than as the powder.

Be sure to purchase TETRAsodium EDTA, not DIsodium EDTA. Tetra is for alkaline products like soap. Di is for neutral to slightly acidic products.

More about EDTA and citrate: http://www.soapmakingforum.com/showthread.php?p=509320
ETA: And here's more background: http://www.soapmakingforum.com/showthread.php?t=52456

PS: My apologies to those who have seen this before. Thought I'd just repeat myself and save a little time.

 

[jiroband]

Interesting. Thanks for the info!

Jim

 

[DeeAnna]

I'm making up a sodium citrate solution this afternoon, but I'm doing it at room temperature, rather than heating it.

My initial recipe:

100 g citric acid
131 g baking soda
134 g distilled water

Theoretically, the yield of sodium citrate is 134 g, so that is why I decided to use 134 g of water.

My goal was to make a 50% solution of citrate and water. I didn't allow for water that the reaction itself is creating, so I think I'm going to end up with a slightly less concentrated solution than I had planned. Small matter.

What's cool is this is an "endothermic" reaction, meaning one that absorbs heat from the environment. My container and the fizzy liquid inside are actually quite cold. The process is slow as well -- I mixed up my ingredients about 3:30 p.m. and the mixture is STILL fizzing gently two hours later.

I'll update this later....

ETA: I updated this recipe -- see Post 83 for the latest version.

 

[Dahila]

DeeAnna thank you so much, I know i should formulate my questions better after 25 years in Canada and thousand and one books I had read, but I am older lady. Forgive me, and thank you.
Galaxy hee it is normal not to understand me, sometime I do not understand myself. Thanks to kind people here, I actually feel welcome, on the forum)

 

[SunWolf]

<snip> Stir the citric acid into the water you will use to make your lye solution. Add the lye to the water and proceed with your recipe as usual. <snip>

PS: My apologies to those who have seen this before. Thought I'd just repeat myself and save a little time.

Thank you, thank you, thank you for repeating yourself! It has finally sunk into all the holes in my swiss cheese brain, and the math finally makes sense. It's been fun making my brain stretch a bit, it's been a while. :grin:

However, I have a question about the above instructions about how to add the CA. I use raw goat milk as full liquid for almost all of my recipes...citric acid and milk do not play well together...

...well, unless, of course, you are actually wanting to make cheese!! But that's a whole 'nother obsession I'm just getting started on!

So, since I want to make soap instead of cheese, can I add the additional lye to the lye solution, and blend the CA into my oils?

I'm thinking the oils will dilute the CA a bit to keep the milk from curdling, and the extra lye will already be working on the goat milk, so it should work out OK?? Maybe??

 

[galaxyMLP]

Considering you have a huge excess of lye (a base) and are adding only a small amount of CA that will be neutralized, I would still add it to the lye solution in your case. Add the CA after you make up you lye solution with the excess lye to neutralize the CA.

This is because in your case, the goats milk won't even "see" the acid to react with it and curdle. The lye will "see" the CA and react with it. This means you have no more acid left in your solution but still have the lye left to react with your oils in your recipe.

You can't add CA to your oils because it is not soluble in oil (it won't dissolve!) That means you might get granules of CA in your soap if it doesn't get a chance to dissolve when you add the lye water!

Please note for all those interested above, in this case I am referring to adding citric acid and not sodium citrate as I have been talking about this whole time. Sodium citrate does not need any extra lye.

You know, you could also just make up sodium citrate with the baking soda and not have to worry about neutralization at all!

 

[SoapSap]

Is sodium citrate also used to prevent DOS, just as TRISODIUM Citrate?

 

[DeeAnna]

SunWolf -- I agree with Galaxy that the citric acid should be dissolved in a water-based liquid to make sure it dissolves completely. I can also appreciate your concern about the acid curdling your soap. Perhaps the compromise is to dissolve the citric acid in a small amount of water and when it is dissolved, then blend that liquid into your fats. You should be able to dissolve citric acid in an equal weight of water or a bit more, so it won't take much water. Galaxy makes an even better point that sodium citrate may be the best thing to use, because it avoids the whole issue of exposing your milk to an acid at any point in the game.

Update on my experiment -- it's now about 6 hours since I first mixed up my ingredients. The fizzing has stopped. What I've got is a whitish crystalline material in a water-clear but slightly syrupy liquid. The effect is like a partly melted slushy (snow cone). I'm going to leave it alone overnight and see what it looks like in the morning. I'd like this to be a fully liquid solution, so it looks like I'm going to have to dilute this further to reduce the concentration and get the crystals to dissolve. I thought from my reading that sodium citrate is soluble in water up to a 50% concentration, but obviously I'm wrong on that point!

I should add -- If you are considering trying this for yourself, I want to warn you to mix your ingredients in a generously large container. The container should be at least 5 or 6 times larger than the volume of your ingredients, because this stuff foams up A LOT. For example, I mixed my 365 grams of ingredients in a 1 liter beaker and that wasn't quite big enough -- I had to watch it like a hungry hawk for about 45 minutes. It will also work better if your container is as wide or wider as it is tall, because the foam that is created will break down easier in a wide, shallow container than in a tall, narrow one. Plan to sit with your experiment for at least an hour and stir as needed until the foaming slows down and doesn't threaten to overflow. At that point, you can put your experiment in a safe place out of reach of pets and children and let it quietly fizz away for a few more hours on its own.

 

[DeeAnna]

Sodium citrate IS trisodium citrate, at least this is the typical version you'll find in general commerce. You can get mono- and di-sodium citrate as well for specialty uses.

"...Trisodium citrate has the chemical formula of Na3C6H5O7. It is sometimes referred to simply as sodium citrate, though sodium citrate can refer to any of the three sodium salts of citric acid...." https://en.wikipedia.org/wiki/Trisodium_citrate

 

[commoncenz]

DeeAnna, don't know how much (if any) this helps, but 1 gram of SC dissolves in 1.3 grams of water at around room temperature, so it's not a true 1:1 ratio for solubility.

https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Fluka/Datasheet/71401dat.pdf

Solubility is mentioned under "Preparation Instructions"

 

[DeeAnna]

Good stuff, Patrick -- thank you for digging that up; I appreciate the info. A 1:1.3 dilution would be about 43% concentration of sodium citrate. From a practical sense, I'd probably use a 40% concentration max to allow for temperatures cooler than 25 C (77 F).

I diluted my mixture to a 33% concentration (1 part citrate to 2 parts water) this morning. (That was before I read your post, Patrick, or I would have tried a 40% concentration instead!) Almost all of the crystals dissolved within seconds, but there is a small amount of solids remaining. I'll see if a bit of time will help the last bits to dissolve.

 

[sudsy_kiwi]

Just to go off on a wee tangent, is it possible to add SC or CA to M&P soap? And if so, how would you suggest doing it?
With our hard water here, even M&P seems to dry my skin something terrible.

 

[DeeAnna]

I don't have any M&P experience, so I can't say for sure, but I'll offer my opinion based on things I've heard from people who do M&P.

I rather doubt it would work well to add either one, given the cautions I hear from others about adding other ingredients to this type of soap. If it would work to add a chelator, then I'd use sodium citrate only. You'd only want to add citric acid to a soap if there is enough extra lye added for the acid to be able to turn into sodium citrate. Is there extra lye in M&P? If not, then any added citric acid would probably break down the M&P soap and make a mess. That wouldn't be a good idea.

I also want to add that hard water makes soap scum, which can be sticky and unpleasant on the skin, but soap scum isn't the same as the soap being drying to the skin. That comes from the formulation of the soap itself. I have heard some formulations of M&P can be harsh, so maybe you need to consider another base? Many people swear by SFIC bases, if you're looking for a suggestion. Again I'm just repeating what I've heard -- I don't have personal experience.

 

[galaxyMLP]

I agree about the soap scum not feeling drying to the skin. It may feel a little itchy and sticky but it shouldn't feel drying. Since MP soap does have some water and other solvents in it, you may be able to add a small amount of SC to it and see if it dissolves just adding it directly to melted soap

Alternatively, SC may dissolve in glycerin a little bit. Try warming about 15 grams (~1 tablespoon) of glycerin and adding 1-5 gram of SC. Start w/ 1 gram and keep adding SC till it won't dissolve any more.

How I would do it:

1. Place 15 grams glycerin in a little bowl and warm it to ~100 F
2. Weigh out 1 gram of SC into 5 containers (total, 5 grams)
3. Add 1 container to the glycerin
4. Stir stir stir
5. Repeat until you stop getting it to dissolve.

You can add up to 1 tablespoon glycerin to 8 oz of MP soap.

 

[commoncenz]

OK, just got done taking a batch of the solid form out of the pot and placing it in the oven to see if I can get it to dry a little more. What I did was to take it out of the pot when it was still very moist and put it into the oven (on parchment paper) at 210 degrees Fahrenheit. I will watch it carefully and use my steel spoon to keep it broken up a bit. Maybe after it is "dry" I'll run it through the blender on pulverize to see if I can get a powder.

I wanted to try to make the solid state SC first as I am a glutton for punishment. :mrgreen:

I would add pics, but my phone is acting funny.

 

[DeeAnna]

Nice refinement to the method, Patrick! I like the idea of heating the sodium citrate to dryness in the oven or in a dehydrator if a person has one. Much less chance of overheating than the stovetop method. While I'm sure the stovetop would work fine for many, I'm definitely too absent minded. :shifty:

 

[commoncenz]

Can't take full credit for that. I had mentioned possibly using the microwave to complete the drying process and Galaxy correctly pointed out the dangers of that method and suggested the oven and the temperature.

Btw, if you keep an eye on it in the oven, as it starts to dry, you can break it up into a very usable powder form by folding the parchment paper and using the back of the spoon. Do this a few times each time that you check on it and breaks down nicely. Well, so far it has. I've had it in the oven for about an hour and have checked it about 3 times using the fold/spoon method to break it down each time.

 

[commoncenz]

OK, son returned home and his camera is working. So, here is a picture of the SC I made tonight. I used Galaxy's original recipe and completely dried it in the oven. I am wondering though because Galaxy stated the theoretical yield was about 268 grams. I ended up with 290 grams. However, as far as I could tell, the citrate was as dry as could be and I was able to get it into a powdered form by using the method I described above and then using the spoon to grind it down after it was dry and "crunchy".

 

[DeeAnna]

Nice! SC can make a hydrated form where some water is chemically bound to the main molecule. That could explain the weight difference. Another possibility is incomplete reaction so some baking soda or citric acid is left over. I vote for option 1.