Soapmaking 101

Several years ago we purchased half a beef from a local farm. Along with the meat the processor gave us several buckets of lard. The meat was quickly eaten by our family but the lard languished in the freezer until the freezer failed a couple of months ago. Not wanting to just throw the lard out I decided to make something more useful out of it. The lard could be used to make biodiesel but I don’t have a working diesel vehicle to use it in. My mother made soap and I have a book on soap-making that I got as a gift.   So I decided to use the lard to make soap.

The book I have is “Soap Maker’s Workshop, The Art and Craft of Natural Handmade Soap” by Dr. Robert S. and Katherine J. McDaniel. The book describes several ways of making soap. The first I really don’t call “making” as it involves melting down already made soap and adding things like scents and colors then molding it into bars or fancy shapes. The local craft shop has supplies for this process,  basic soaps, molds, scents, colorants and other additives.  Seems like everyone is terrified of working with lye. Then there is the cold process and hot process. The cold process is not really cold you just don’t add any heat after the ingredients are brought up to temperature. The only advantage of the hot process that I can see is that it takes a little less time.

One of the suggestions in the book that made things a lot quicker and easier is the use of a stick blender also called an immersion blender. The is a kitchen gadget that I use to mix up things when I am cooking, particularly sauces  that have come out lumpy. When you add the lye solution to the oil it has to be stirred to get the lye to react with the oil. The better it is mixed the faster the saponification process  occurs. The mixture has to be stirred until the batch begins to thicken or as they say trace. Tracing means that when you dribble the mixture from a spoon into the pot it leaves behind a trace on the surface of the liquid. At this point the soap should be poured into molds to continue to set up. If you wait too long, as I found out with one batch it will get too thick and not pour well into the molds.

You can purchase soap making molds but for the batch size I wanted to make this would be a lot of molds and I don’t expect to keep making soap after my supply of lard runs out. I chose to use 1 quart paper milk cartons for the molds since we had a number of them available. After the soap has set up in the carton you can peel off the paper and cut the block of soap into bars with a knife. It cuts quite easily.

Things have gotten a lot more precise than when my mother was making soap. The book has tables showing the various fats and oils that can be used to make soap. The tables list the SAP (saponification value) and INS value of each oil and fat. The SAP is the amount of lye needed to completely convert that fat to soap. The INS value relates to the quality of the soap. Someone has found out by measuring a lot of different soaps that the average INS value of the measured soaps is 160. This seems to be the ideal value for making bar soap. Because each oil or fat has a different INS value you can combine different oils and fats to make a soap with the “ideal” INS value of 160.

It turns out that in the tables only coconut oil has an INS value greater than 160 so to make a soap with an INS of 160 you have to use coconut oil. The book has a number of recipes/formulas for soaps and sure enough they all have coconut oil as an ingredient. I did not have any coconut oil and had never used it. It can be purchased online or I finally found some at Walmart, LouAna pure coconut oil. Apparently coconut oil is popular in southern cooking but not so much here in Iowa.

One thing that I was surprised about the book was that while it had a number of recipes and had the SAP and INS tables it did not go into the details of creating your own recipe. Most of the recipes in the book  called for a large number of different oils which I do not have so I set about making my own recipe that had the lard as the major ingredient. I also have some castor oil which needs to be used up. So I  made a three fat soap recipe using lard, castor oil and coconut oil. The table below lists the three ingredients and their respective INS and SAP values.

Symbol Fat INS SAP
A Lard 139 0.141
B Coconut Oil 258 0.191
C Castor Oil 95 0.129

I decided to make a batch of soap using 4 pounds (64 oz) of fats. The next thing that needs to be done is to calculate the amounts of each ingredient that will give a INS value of 160 and add up to 64 oz, assuming you want to try and make an “ideal” soap. I have just described two equations giving the relationship of the fats so they can be written out.

A+B+C=64   and

\frac{A\cdot I_{a}}{A+B+C}+\frac{B\cdot I_b}{A+B+C}+\frac{C\cdot I_c}{A+B+C}=160

There are two equations and three unknowns so this cannot be used to determine the amount of each fat. The castor oil is an additive in soap not usually a main ingredient so I decided to use 4 oz of the castor oil in the 64 oz batch. Substituting the known values into the second equation gives:  \frac{A\cdot 139}{64}+\frac{B\cdot 258}{64}+\frac{4\cdot 95}{64}=160

Working with the first equation we get B=60-A Substituting 60-A for B in the second equation and solving gives:

A= 47.23 oz B= 12.77 oz and the 4 oz I chose for C.

The next step is to calculate the amount of lye needed in the formula. The SAP values shown in the table indicate the amount of lye needed to just convert that amount of fat to soap.  So to calculate the amount of lye needed for the combination of fats we can use the equation:

Lye=A\cdot S_a+B\cdot S_b+C\cdot S_c

This works out to be 9.62 oz of lye for my recipe.  When making soap you do not want to convert all of the fat to soap. A little fat should be left to make the soap less harsh and make sure there is no leftover lye. This is called the lye discount and 3% is recommended when castor oil is used so multiplying 9.62 by 0.97 gives  9.3 0z of lye to use.

The book does not say much about the amount of water to use but in most of the recipes the ratio of water to lye is 2.05 so this recipe needs 19 oz of water. To sum up the recipe:

Lard 47 oz
Coconut Oil 12.8 oz
Castor Oil 4 oz
Lye 9.3 oz
Water 19 oz

The equations can be extended to any number of fats but you have to pick the amounts for all but two. Don’t choose the amount for the coconut oil, let the calculations tell you how much because it is possible to come up with an unsolvable equation if too much or too little coconut oil is picked. You can also choose the batch size you want to make by setting the first equation equal to the batch weight. You can use any unit of weight or mass in these equations as the INS and SAP values are unit-less.

I have made two batches of soap with this formula and I am quite pleased with the resulting soap.

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