lye solution/concentration vs. water as % of oils

[BlackDog]

I did my first batch using lye concentration instead of water as % of oils this weekend, and I was shocked - SHOCKED - at the amount of time I had to play with color, even using less than full water. Of course my hanger swirl was an utter fail in terms of what I wanted vs. what I got, but I'm a total convert now! Thanks to the forum for giving me the push to switch.

 

[DeeAnna]

"... Of course my hanger swirl was an utter fail in terms of what I wanted vs. what I got..."

Oh, gosh, welcome to the club! <...insert secret Club Handshake here...>

 

[Dharlee]

Omgosh I get it now. Except for the 190/67 numbers at the beginning I understand WHY lye concentration is different from water % AND why it makes a better formula. As long as I don't have to figure out the math myself I don't need to totally get yhose numbers lol. DeeAnna your analogy was genius. Thank you!

 

[DeeAnna]

Dharlee --

I wrote in Post 11: "...In the 100% lard example, the lye solution concentration is 67 / (190 + 67) = 26%...."

The 67 is the lye weight in grams. The 190 is the water weight in grams. If you look at the first SoapCalc printout at the bottom of that Post 11 you can find these numbers. When you mix the lye and water to make the lye solution, that's what you end up making -- a mixture that is 26% NaOH.

Whether this math makes sense or not, it doesn't matter. Just use a good soap recipe calculator and it will do this math for you. I don't do all this by hand for my soap recipes either!

 

[Dharlee]

Dharlee --

I wrote in Post 11: "...In the 100% lard example, the lye solution concentration is 67 / (190 + 67) = 26%...."

The 67 is the lye weight in grams. The 190 is the water weight in grams. If you look at the first SoapCalc printout at the bottom of that Post 11 you can find these numbers. When you mix the lye and water to make the lye solution, that's what you end up making -- a mixture that is 26% NaOH.

Whether this math makes sense or not, it doesn't matter. Just use a good soap recipe calculator and it will do this math for you. I don't do all this by hand for my soap recipes either!

I most especially am grateful for the last part. I had a sticker on an old car for years that said, "I can't be overdrawn! I still have checks left!" and it's pretty much me lol. Kidding aside, I just don't want to do the math although I am sure I could learn. But I DO want to know what to do and most importantly why. I think if I know why, it will stay with me and I won't forget it. (I hope lol)

 

[cgpeanut]

As you noted, using "water as % of oils" causes the water amount to vary, depending on the saponification value of the oils. A recipe using "water as % of oils" will have a less concentrated lye solution when using fats with lower sap values (say olive) and a more concentrated lye solution for fats with higher sap values (say coconut).

This is exactly the opposite of what you might want.

For example, olive oil saponifies slowly -- sometimes too slowly -- when made with a more dilute lye solution. It does best with a moderate or even a more concentrated lye solution. Coconut oil saponifies quickly and easily, so it may be desirable to use more water with a recipe high in coconut oil. More water will slow down saponification so you can have more time to swirl and to minimize the chance of overheating in the mold.

Your focus appears to be on what happens after the soap is made, but a person has to consider what happens during saponification too.

question for DeeAnn. Is the saponification value of a given oil an indication of how fast it will saponify as well as how much lye it takes to saponify??

 

[DeeAnna]

"... Is the saponification value of a given oil an indication of how fast it will saponify as well as how much lye it takes to saponify??..."

No, the saponification value doesn't tell you anything about the rate of the chemical reaction. It is only telling you how many fat molecules are packed into a given weight. A higher sap value = more fat molecules per ounce or gram. If you have more molecules in a given weight of fat, then you need more NaOH molecules to properly saponify that fat.

 

[DeeAnna]

Update -- There is one thing in particular I want to add to my previous answer to make it more complete --

The rate of saponification depends on the shape of the molecule and the kinds of atomic bonds. You could have two molecules that have similar saponification values, because both have about the same quantity of fat molecules per gram. You might find, however, that one will saponify slower than the other. This is due to the different shapes of the fat molecules and/or how the atoms are fastened together (for example, the presence of double bonds vs. all single bonds, for the chemistry folks).

So the amount of lye needed to saponify a gram of fat doesn't really tell you how fast that gram of fat will turn into soap.

 

[Steve85569]

Update -- There is one thing in particular I want to add to my previous answer to make it more complete --

The rate of saponification depends on the shape of the molecule and the kinds of atomic bonds. You could have two molecules that have similar saponification values, because both have about the same quantity of fat molecules per gram. You might find, however, that one will saponify slower than the other. This is due to the different shapes of the fat molecules and/or how the atoms are fastened together (the presence of double bonds vs. all single bonds, for the chemistry folks).

So the amount of lye needed to saponify a gram of fat doesn't really tell you how fast that gram of fat will turn into soap.

I am assuming that this is NOT saturated/ Unsaturated ratios and is the actual atomic make up of the molecules. i.e. no simple ratio and proportion equation to determine the amount of lye to oil.

 

[DeeAnna]

"...this is NOT saturated/ Unsaturated ratios..."

You are correct. I am talking about the physical structure of the atoms themselves, not about bulk properties.

 

[Punkin2x74]

Thank you Ladies and Gents. I've been doing more and more being a hobbiest with ambition. I want to understand the more in-depth of soap making and not just regurgitating the information read on sites and blogs/groups. Thank you.

 

[HappyHomeSoapCo]

Ok. I am converting my methods. Thank you so much for this thread, which I've read half a dozen times, lol. But a question i have is, when comparing the same recipe in Soap Calc to SoapMaker3 program, the numbers dont match. I am just setting up and learning SM3 and I want all my recipes this year to be set up with lye concentration. For peace of mind, i compared it to soapcalc, and its not exact, but close. Anyone experience this?

 

[Susie]

Each soap calculator is going to be a tiny bit different. That is because they are using different SAP values for the oils. Just pick one and stick with it.

 

[houseofwool]

I found the same thing. It is because each program has a slightly different SAP value for the oils. It isn't a problem.

 

[DeeAnna]

What Susie and HoW said -- spot on advice.

I want to add another thought -- if SM3 allows you to use the actual lye purity (rather than assuming it's 100% as many soap calcs do), then the lye purity will also affect these numbers. (I have never used SM3, so I don't know what it does or doesn't do.)

 

[macster2075]

I've always soaped at 33% Lye Concentration, not because I understood it too well, but because that's what I have read for years
But anyway.. I have noticed that the Calculator at Summerbeemeadow's website says to use lye at around 30% concentration when determining the amount of oils to use for a specific mold size.

Once you input your mold dimensions, it will tell you the amount of oils and water to use, and if you input that info in SoapCalc, you'll notice that 30% lye concentration is used...very interesting... once I noticed that, I changed to 30% Lye Concentration