# Water Discount and Oil Calculation for the Mold

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Supporting Member
Hey all. I actually did my due diligence before posting this, so if it's already answered out there somewhere, please accept my sincerest apologies and kindly redirect me to the appropriate post.

I am going to water discount my next batch...nothing big...maybe 5% to see if it helps reduce ash. My question is this: When you use the standard calculation 40% calculation for oils to mold, that assumes the remaining 60% is a combination of lye and water/fluid. Now I'm a pretty smart guy, but I cannot figure how to back into the proper amount of oils to achieve the size bars I need. Maybe I'm overthinking it, but since the standard oil calculation is based on volume while the oil/lye/water calculation is based on weight, I can't reconcile how to back back into the proper oil weight to start with. Nobody likes to end up with great soap but wonky-sized bars.

Obviously, with less water, to achieve a given volume, I will need to increase both the oil and lye volume, but I don't know by how much. Any help? Do any of the the calculators do this math for you?

#### Lin19687

##### Well-Known Member
I think you may need to have the calculations for the Mold size.
There is a sticky or post about how to figure out how much to put in a mold.
Maybe in the beginning section?

#### DeeAnna

##### Well-Known Member
Discount your water from what? I'm not being snarky here -- there's no set, agreed-upon, consistent definition of exactly what "full water" is that one should "discount" from. Because these concepts are so imprecise, it's best to use and talk about water in terms of lye concentration or water:lye ratio.

Here's how I'd do it using lye concentration --

In my last recipe for a total of 1600 g fats, the total water content is 621 grams at 28% lye concentration. The total paste weight (fat + NaOH + water) at 28% lye concentration is 2620 grams.

If I raise the lye concentration to 33%, the water content drops to 490 grams and the total paste weight is 2462. The reduction in weight is 2620 - 2462 = 158 grams.

Leaving the lye conc at 33%, I would gradually increase the fat weight, recalculate the recipe, and watch the paste weight until it equals the total paste weight for the original recipe.

In my example, I'm looking for the total paste weight to rise to 2620 grams and that happens at 1690 grams of fat. Now the total paste weight of the revised recipe (at 33% lye conc) equals the paste weight of the original recipe (at 28% lye conc).

I know fat is less dense than water, but IMO this answer is sufficiently close enough.

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Supporting Member
Discount your water from what? I'm not being snarky here -- there's no set, agreed-upon, consistent definition of exactly what "full water" is that one should "discount" from. Because these concepts are so imprecise, it's best to use and talk about water in terms of lye concentration or water:lye ratio.

Here's how I'd do it using lye concentration --

In my last recipe for a total of 1600 g fats, the total water content is 621 grams at 28% lye concentration. The total paste weight (fat + NaOH + water) at 28% lye concentration is 2620 grams.

If I raise the lye concentration to 33%, the water content drops to 490 grams and the total paste weight is 2462. The reduction in weight is 2620 - 2462 = 158 grams.

Leaving the lye conc at 33%, I would gradually increase the fat weight, recalculate the recipe, and watch the paste weight until it equals the total paste weight for the original recipe.

In my example, I'm looking for the total paste weight to rise to 2620 grams and that happens at 1690 grams of fat. Now the total paste weight of the revised recipe (at 33% lye conc) equals the paste weight of the original recipe (at 28% lye conc).

I know fat is less dense than water, but IMO this answer is sufficiently close enough.
Thanks. I think it was the last line that I was looking for. Basically, keeping the fat/ratio the same, increase them both enough to compensate for the reduced volume of water.
On the "standard" fat-to-water ratio, I was referring to the Soapcalc default of 38%. I've never been brave enough or felt the need to adjust it, but I'm hoping reducing it will reduce ashing.

I think you may need to have the calculations for the Mold size.
There is a sticky or post about how to figure out how much to put in a mold.
Maybe in the beginning section?
I know how to calculate (at least the most popular method) for determining oils-to-mold. It's basically volume x 40%. I was trying to figure out how much to increase that percentage to compensate for less water which would obviously lead to less total volume.

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A

#### amd

Suggest to switch from using "water as % of oils" and use lye concentration or water:lye ratio. You'll get more consistent results for your soap making.

Supporting Member
Discount your water from what? I'm not being snarky here -- there's no set, agreed-upon, consistent definition of exactly what "full water" is that one should "discount" from. Because these concepts are so imprecise, it's best to use and talk about water in terms of lye concentration or water:lye ratio.

Here's how I'd do it using lye concentration --

In my last recipe for a total of 1600 g fats, the total water content is 621 grams at 28% lye concentration. The total paste weight (fat + NaOH + water) at 28% lye concentration is 2620 grams.

If I raise the lye concentration to 33%, the water content drops to 490 grams and the total paste weight is 2462. The reduction in weight is 2620 - 2462 = 158 grams.

Leaving the lye conc at 33%, I would gradually increase the fat weight, recalculate the recipe, and watch the paste weight until it equals the total paste weight for the original recipe.

In my example, I'm looking for the total paste weight to rise to 2620 grams and that happens at 1690 grams of fat. Now the total paste weight of the revised recipe (at 33% lye conc) equals the paste weight of the original recipe (at 28% lye conc).

I know fat is less dense than water, but IMO this answer is sufficiently close enough.
I understand there is no stanard agreed upon water percentage, but I can tell you at 38% water, the volume x .40 calculation produces exactly the size bars I plan for. If I'm going to decrease the volume of water, I will need to compensate with more fat and therefore more lye. I was just trying to see if there is an accuarate mathematical way to do it versus winging it. Obviously, I can overshoot the mark and either have extra soap to pour into a side mold or trim any extra off. I was just hoping to avoid waste.

View attachment 38106
Suggest to switch from using "water as % of oils" and use lye concentration or water:lye ratio. You'll get more consistent results for your soap making.
Thanks. I'll try it.

The problem I see with that is that I will have already started with the problematic number, the weight of oils, which I would have obtained using the volume x .40 calculation.

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#### Lin19687

##### Well-Known Member
Ahhh, I agree with @amd & @DeeAnna
The Lye concentration is easier , I think...

I would figure out how much you need total and then play with the % and go from there.

#### DeeAnna

##### Well-Known Member
@amd is right. If you always use "38% water as % of oil" for all your recipes, the water content in proportion to the alkali (NaOH) can vary all the way from about 26% to 31% depending on the fats you use.

To make matters worse, "water as % of oils" will make you use more water for recipes that are more successful if made with less water (olive il soap for example) and less water for recipes that work better if made with more water (coconut oil soap for ex).

You get more consistent results if you key the water content to the amount of NaOH used, not the amount of fat used.

Supporting Member
@amd is right. If you always use "38% water as % of oil" for all your recipes, the water content in proportion to the alkali (NaOH) can vary all the way from about 26% to 31% depending on the fats you use.

To make matters worse, "water as % of oils" will make you use more water for recipes that are more successful if made with less water (olive il soap for example) and less water for recipes that work better if made with more water (coconut oil soap for ex).

You get more consistent results if you key the water content to the amount of NaOH used, not the amount of fat used.
I am beginning to understand the truth in what y'all are all saying. I was just trying to get the volume right, but clearly there are more adjustments that I can consider. It just makes sense that oils with a higher melting point (e.g. OO) wouldn't need as much water as hard oils like lard/CO/Palm. Thanks everyone for the input.

If making soap was easy, everyone would do it.

Supporting Member
Last question...When you use the 91% alcohol, when do you start spraying? As soon as it's molded or after it sets up a bit.?

#### Lin19687

##### Well-Known Member
after pouring. Some do it again later.
I think someone said soap queen did it like 4 times.

I have not had much luck but everyone has different recipes and area of working (living area as in state)

A

#### amd

I spray as soon as it's molded, and then continue to spray several times over the next two hours or so. (Probably 3-4 times total) Royalty Soap mentioned in one of their recent videos that they spray up to 10x in the first hour.

#### Lin19687

##### Well-Known Member
Also want to add that ...

For me I am looking to make a soap fit a box, so it HAS to fit AFTER CURE.
I have figured it out to just fit in there with almost no room to spare.

Mainly by trial and error because I have a longer mold

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#### shunt2011

##### Moderator Emeritus
Supporting Member
I spray mine as soon as it's in the mold and then will do it again 4 or more times over then next hour or two. Keeping it covered until fully saponified it really the key for me. I generally get a ton of ash on my salt soap in individual molds. So, I spray well with alcohol, then I just covered them with plastic wrap for 12 or so hours. I then unmold and cover them fully for another 24-48 hours then put them to cure. I have absolutely no ash on any of them.

#### DeeAnna

##### Well-Known Member
...oils with a higher melting point (e.g. OO) wouldn't need as much water as hard oils like lard/CO/Palm....

The melting temperatures of the fats don't relate to what is best for the water content in a soap recipe. In geek speak -- correlation doesn't mean causality. In plain words, melt temp has little or no influence on how a fat saponifies in response to water content.

The "normally solid at room temp" fats -- lard, tallow, palm, butters, palm kernel, coconut, babassu, etc. -- vary in their response to different lye concentrations.

High palmitic-stearic fats -- lard, tallow, palm, butters -- are fairly tolerant of reasonable variations in the amounts of water. They tend to saponify moderately easily and tend to make a relatively hard soap at the time of unmolding.

High lauric-myristic fats -- palm kernel, coconut, babassu -- saponify quickly and tend to overheat if saponified without sufficient water.

Olive oil and other mono- and poly-unsaturated fats (aka the fats liquid at room temp) tend to saponify slowly especially as the water content goes up in the recipe.

Please notice I'm talking about fatty acid composition, not melt temp, when I generalize about the rates of saponification.

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