Recipe size- fl oz to actual weight

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Jul 25, 2015
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Good morning,
I have made soap several times before and I'm familiar with the precautions that need to be taken. I am a teacher and I currently have an advanced physical science class. This year I want to make soap when I teach about physical and chemical changes.

I am trying to make up a recipe in order to make 30 bars of goat milk soap that are 6 fluid ounces each (based on the molds I have). I need help coming up with the recipe and supply list to turn in to my administrators for funding. I just want a simple recipe with coconut oil, palm oil, goat milk, olive oil, and lye. I keep getting confused when reading online trying to convert back and forth between weight ounces and fluid oz. I need at least 180 fluid ounces? Help!
If this is for a science class I would not use goats milk. You would be wanting to show the reaction of the oils and the lye. I would stick with very simple ingredients. Milk can cause problems in soap such as overheating and scorching - why bother with it.

If I were trying to show soap making for educational purposes I would make a simple Lard, coconut, castor soap and I might scent it if I was going to give the final product to the class but even that I would think twice about.

As for the amount you want, simply use a lye calculator and adjust or resize your recipe to fit what you need.
I agree about the milk - just use distilled water would be my vote.

For the recipe using what you have avaialble I would say something like:
60% palm or lard (I like lard)
25% Coconut oil (if you can get castor oil sub 5% castor and 20% coconut)
15% Olive oil
1 tablespoon sugar ppo dissolved in the water before adding the lye
5% superfat

Some might say that the CO is a little high - but these are grubby teens :)

Just use those percentages and keep changing the amount of oils in the weight of oils box in the soap calculator (like until it spits out 180 ounces total for the soap. I would go a little over and have some small molds handy for extra.
I agree with Dorymae. You say you don't have experience with milk soaps, and your primary goal is to demonstrate saponification as a chemical reaction, so keep it simple and stick to what you know you can do well. A class demo is not a good moment to expand your soaping horizons.

As far as fluid ounces of soap vs. weight ounces ... as you know, they are not the same. A 16 wt. oz. recipe of soap is not 16 fluid ounces. The conversion will depend on your recipe, since the density of fat is less than the density of water and the density will vary a bit with the ratio of fats to water. You can estimate this density, sure, but the best way to deal with this problem is to simply try a test batch. A test batch will also let you check your technique, method, and recipe before you do the demo. It's one thing to make soap in the kitchen without distractions and quite another to do it in a classroom or lab environment with a bunch of people around, especially fidgety kids whom you are responsible for.

Decide on a recipe and a size for your test batch. If the test batch is 1 to 1.5 lb (16 to 24 wt ounces) then find 5 molds that are sized to hold 6 fluid ounces each. Make the soap, fill the molds to the 6 fl. oz. mark. Find out how many molds that recipe will fill. Use a ratio problem to resize your test batch ingredients to determine the proper size batch for your demo.I'd add a wee bit more to the total size just to make sure you have enough to fill all the molds plus one or two. You might have some spillage or other minor mishap.

ETA: And have you ever made a batch of soap that large? You might want to consider making a smaller batch for the demo -- one that is closer to the batch size you normally make. Pre-make the rest of the soap bars (or all of them) in advance for giving to the kids or for whatever else you are planning to do with the bars.
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I agree regarding the goat's milk. If you are absolutely determined to use milk, canned or powdered is MUCH easier than fresh.

Regarding quantities -

1 ounce of oil by weight is roughly 1 ounce by volume. This is not good enough when calculating your recipe, but it is good enough when calculating the amount you will need for your mold size. Your recipe will be roughly 1/3 water and 2/3 oils. So, if your mold is 180 ounces, your recipe will use roughly 60 ounces of water and 120 ounces of oil. You can use that as a starting point to plug your numbers into a lye calculator.

I think this is what you need to determine how much supplies you need for your molds, if I understand the question correctly. You know the volume of the mold, but need to figure out the weight of what goes into the mold.

Unless you are having each student mix their own batch, I would also pre-make most of the bars. And totally skip the milk as the process to use it may become confusing in the point of the lesson. Stick with a basic emulsion + chemical reaction lesson.
Aye, if you work out the cl volume of the mould and multiply it by 10, you have the cm3 of the mould. Times that by 0.7 and you have a good target for the oil weight (in grams) needed. Should have - I am not a maths wiz. This is based on the usual calculation of H x W x L (cm) of a mould x 0.7 being the way to work out oils needed in grams. The H x W x L being the volume in cm3.......

But as has been said, make enough bars before hand for the children, then do a demo with a smaller batch. They won't wait for the 4 week cure!
Yeah, I was overthinking the weight vs volume thing. Y'all are making more practical sense than I am.

If you do a recipe that weighs a total of 180 ounces, you will make a little more soap than would be needed for 180 ounces volume. That approximation is good enough for buying supplies.
I see from your first post on SMF that, as of 7/25, you had not yet made soap, so I want to emphasize the cautions you are getting here -- keep the demo recipe fairly simple and small, don't over-reach your current level of ability, and demo only what you ~know~ you can do well.
I have yet to try a mammal milk soap - the idea just squicks me out. Now coconut milk I like :)
Hmmmm. I kinda wish the OP would reply. In the two threads he/she has started, the only post from OP is the first one. He/she has given no feedback -- were our suggestions are helpful, is there more detail to better explain the problem, asking other questions, etc. Feels like being at a party and suddenly learning the host is sitting in the kitchen reading a book or gone to bed or something. :?:
I agree, D. I have sometimes started threads and then lost track of them, but not often, and then feel guilty when I remember. It is kind of rude to ask for help, have people spend time answering, and then not take the time to reply. IMO, it is also different w/someone who spends a bit of time here, espec. at first, for a new poster it is really not a good sign.

This person has received some excellent advice here, I hope s/he takes it, o/w very possible an in-class experiment will not be very successful, and it would be a great idea if it worked.

ETA: I guess it's possible that the OP is just really busy (eg, has a fuller life than me :)) and will be coming back to answer, I hope so and apologize in advance if that is the case.
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Yes, I agree that could be the case. I have to say when I start a thread, I'm usually curious to see what the response is and what good suggestions I'll get, so I check SMF even more often than usual!
Hmmmm. I kinda wish the OP would reply. In the two threads he/she has started, the only post from OP is the first one. He/she has given no feedback -- were our suggestions are helpful, is there more detail to better explain the problem, asking other questions, etc. Feels like being at a party and suddenly learning the host is sitting in the kitchen reading a book or gone to bed or something. :?:
What is OP?

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