How do they know the SAP values?

[ericllucas]

I know this is a strange question. Does anyone know how a chemist might determine the SAP values (for NaOH) of a mystery vegetable/animal oil sample?

I found ASTM D5558 - 95(2011) Standard Test Method for Determination of the Saponification Value of Fats and Oils on the web, but they want $35 for two PDF pages. Ouch.

Some on this site use all the right words in the right order and lead me to believe they might know how SAP is determined.

Thoughts?

Okay, here is what I'm thinking. I can get oils/fats in a blend. I don't know the blend, so I can't calculate the recipe using percentages of a single blend. I want to use it to make soap but need the SAP value of that particular mix of oils/fats. Is there a spiffy junior-chemist way of figuring it out?

 

[tlm884]

Essentially, lye is a base and oil is an acid. A SAP value is how much lye is required to neutralize 1 gram of oil (someone can correct me if I'm wrong)

So, essentially its a titration reaction. You add a known concentration of base to an unknown concentration of acid and keep adding base until the pH of the reaction reaches neutral (this is done using a pH indicator such as phenophetalian which is pink in a basic solution and turns colorless when the pH goes below a certain point. So when the solution goes from pink to clear and after a few seconds it goes back to pink, its assumed its reached a pH near 7). This then tells you how much base is needed to bring the acid to neutrality.

However, the compositions of oil varies from plant to plant and most SAP values are recorded as a range. For example, Corn oil produced in midwestern USA may have a different oil composition from Corn Oil produced in Saskatchewan due to climate, soil, species of plant, etc.

That is why a 5% superfat is used, to ensure that no excess lye is left unreacted.

 

[Fragola]

The titration method is described in detail many places on the web, it can be goggled, I have seen it.

However, I am not sure you can follow it with enough precision in your kitchen.

My question is: how unknown is the blend you are talking about ? I find it hard to believe that you came across a completely random blend ...

What I would do first is guesstimate the sap value based on the oil properties (melting point, smell, taste, etc.).

After which, you either try a titration, if you think you can do it, or do it through trial and error - make a small test batch (with SF -10 or -15) and split it, with adding a different quantity of superfat to each split.

 

[ericllucas]

My question is: how unknown is the blend you are talking about ?

Okay, I'll fess up. If I get oil from a fryer and wash the oil with baking soda and salt, then filter it, I think I can use it to make soap. I suspect the original oil is a combination of soybean oil, partially hydrogenated soybean oil, palm oil, and/or peanut oil. The person using the cooker pours whatever in there, no consistency. The oil does not smell, well, too much of fish or anything. When the used oil it is poured into a container it separates into three distinct layers after a day - a liquid part at the top, a solid white part towards the bottom, and a layer of crud at the very bottom. I suspect as the oil is used, it becomes more saturated. The oil is usually never worse than stage 4 - no burnt qualities at all.

I do not propose to use soap made from this for fancy colored or scented soap. I think I'd use it to make utility soap for hands, horses, and dogs. Maybe add some grits to it to make scrubby man-soap.

What do you think?

 

[tlm884]

Fryer oil also contains tons of water and possibly acrylamides which are carginogenic. The only thing fryer oil should be used for is biodiesel and evwn then you need to dewater it, filter it, and preform a titration. The high heat also increases free fatty acids in the oil which can cause rancidity. I would never use a bar made from dirty oil

 

[ericllucas]

I would never use a bar made from dirty oil

That says it all. My curiosity regarding using that used oil is now gone, leaving mental bandwidth to wonder about other, new things. Thanks!

 

[tlm884]

Don't get me wrong, I am one for innovation. However, you can be innovative in several other ways when it comes to soap. Unique additives, infusions, water replacements, fragrances, colors and combinations of oils.

Have you looked into beer, eggs, foods, natural colorants, teas, coffees, etc?

Also, biofuels from used fuels may be something your interested in. If you have experience with lye, you already know the safety measures required. Glycerin is also a byproduct of fuel production from waste oils.

EDIT: Another thought, soaps are often used as lubricants industrially. Lithium and calcium soaps made from LiOH and calcium hydroxide are used as greases. I'm sure used oil has an application here.

 

[soapbuddy]

If you don't know the blend of oils, it's going to be next to impossible to get the actual SAP value. Why not use some nice fresh oils instead and not worry about oxidized, DOS prone, used oils?

 

[Fragola]

I suspect the original oil is a combination of soybean oil, partially hydrogenated soybean oil, palm oil, and/or peanut oil.

Based on that info, correlated with the melting point of the oil, you might be able to guess the SAP value with an error of +2%, which is perfectly acceptable (to me).

I haven't tried this, but I believe it's worth a try. Once you are reasonably experienced (which in my eyes means few failed batches together with the understanding of what went wrong and how to prevent such failures).

The only downside I see is that every time you do a batch, you need to make first a small test batch to see if it turns out ok. For the first tries, you may want to make few splits, with different superfat values, just to see how far you are from the truth.

If I get oil from a fryer and wash the oil with baking soda and salt, then filter it, I think I can use it to make soap.

If you mean adding water with baking soda, that will create a serious problem separating the oil from the water. Maybe it will separate after few days or more, I didn't wait that long.

Fryer oil also contains tons of water

Water and oil does not mix, should be easy to separate. Theoretically - in practice certain problems do arise. Here is where you might have a big calculation error, if your oil is mixed with water.

possibly acrylamides which are carginogenic.

Seems doubtful to me, for more than one reason.

This study seems to agree:
http://www.jstage.jst.go.jp/article/jos ... 3/_article

Why not use some nice fresh oils instead and not worry about oxidized, DOS prone, used oils?

Because it's cheap
Obviously this won't be first or even second quality soap. And I am not sure about the legal ramifications, if you plan to sell it.

But even if we would agree that this soap isn't great for the body, there are many dirty things you can wash with soap, where DOS isn't a concern.

Another thought, soaps are often used as lubricants industrially.

We don't have heavy tools at home, but soap helps fixing a stuck zipper.

 

[ericllucas]

Love the replies, thanks very much.

I am going to pass on the used cooking oil.

No, when I meant wash the oil, I meant mix in the dry powders and let it set a little while. Back when I used to work around fryers (five pressure cookers at once), every fourth batch on a cooker, we'd dump a powder in the oil, stir it, let it set, and then filter it. I was going to do the same using baking soda and salt.

I would render the oil to ensure that any water I could get out, I do get out.

In the end, however, if I'm going to spend my time making soap, I want a higher probability of getting a predictable product without having a significant wildcard - the oil. If I reduce the possibility of failure, success is more likely. I am persuaded to think that used cooking oil is too much of a wild-card at this point.

Nonetheless, I think I've learned a lot asking these kinds of questions. Thanks again!

 

[Fragola]

No, when I meant wash the oil, I meant mix in the dry powders and let it set a little while.

How much salt/baking soda would that require ? I have some old oil sitting here and was planning to wash it, but maybe this method will work better.

 

[ericllucas]

We used to dump one cup by volume into five gallons of oil. We'd stir it around and then let it set. It never really dissolved, but it did eventually settle to the bottom. We'd then pump it through a filter, not as fine as a coffee filter, but it was fine enough to get the particles out.

I assume what it was doing was acting like a soap, binding itself to undesirable elements in the oil, so that it could be filtered out.

I don't actually know for sure what was in that powder, but I was told it was just baking soda and salt. I'll go look and see if I can figure it out.

 

[tlm884]

Baking soda might react with the oil though. Oils are acidic and baking soda is basic

 

[ericllucas]

I don't think it could have been baking soda and salt. I found some products that are added to cooking oil and facilitate cleansing of the oil, but they are magnesium silicate. It also occurs to me that commercial frying oil is a blend of many chemicals that stabilize and preserve the oil, unlike the oil we might buy and use at home. Therefore, I'm not sure the powders used in commercial frying would work (as well?) on home cooking oil.

In the end, while it would be nice to be able to recycle cooking oil into bars of soap, and while I'm sure someone has tried it and will try it again, it won't be me