Making Worksheets

No matter how proficient you are at computer spreadsheets, make your first worksheets with good old-fashioned paper, pencil, and a calculator. Many soapers get off track by spending valuable soaping time setting up the spreadsheet. Once you've mastered the paper-and-pencil method, set it up on a computer spreadsheet, if you like.

Even if you decide to use lye calculations or a spreadsheet you've created, make sure you know what you're doing without one. It's not that the calculator will let you down, it's just good practice to be able to rely on your own skills. When you make your first formulas, a lye calculator is a great way to check your work.

A pad of graph paper is a great tool. A pencil with a good eraser is another good one. You don't need a fancy calculator, just one you can use with ease.

First Calculation

Multiply the SAP value of a particular oil by the number of ounces of that oil. The resulting number indicates the amount of lye in ounces that is needed to achieve saponification.

For recipes that use a number of different oils, you calculate how much lye you need for each oil and add the lye amounts to get the 100-percent SAP rate. If you make soap with the exact SAP value, you will have no leftover oil in the batch. Because this leaves you no margin for error, there is a possibility that using the exact 100-percent SAP value could create a lye-heavy batch. It is smart soapmaking practice to use a “lye discount” to ensure a gentle soap.

Taking a Lye Discount

Here is an example of how to take a lye discount; that is, how to alter your lye ratios to make sure you have oils left in your soap after the saponification process.

Coconut oil has a SAP value of .19 when using sodium hydroxide. A recipe that uses 10 ounces of coconut oil would require 10 × .19 ounces of lye, or 1.9 ounces — to saponify — it 100 percent.

A lye discount is a reduction from the total amount of lye needed to saponify the oils to a lesser amount, ensuring there is some oil left over in the soap. It's always a good idea to plan for some extra oil to assure mildness. Too much extra oil, however, can lead to soft soap that spoils easily. A good discount to aim for is between 5 and 8 percent.

For a 10-percent lye reduction in the coconut oil example, multiply 1.9 (the amount of lye) by .1 (10 percent). You get .19 ounces. So, to take a 10-percent discount, you subtract .19 from 1.9 to get 1.71 ounces of lye. To take a smaller lye discount, follow the same formula using smaller multiples — . 02, .03, .04, .05, and so on.

Here's a look at a hypothetical all-coconut batch in three sizes.

Lye Saponification Discount Table

1-lb. Batch

4-lb. Batch

8-lb. Batch

Coconut oil

.190 × 16=

.190 × 64=

.190 × 128=

Water

6 oz.

24 oz.

48 oz.

Lye (100% saponification)

3.04 oz.

12.16 oz.

24.32 oz.

Lye discount 1%

.0304

.1216

.2432

Lye discount 2%

.0608

.2432

.4864

Lye discount 3%

.0912

.3648

.7296

Lye discount 4%

.1216

.4864

.9728

Lye discount 5%

.152

.608

1.216

Lye discount 6%

.1824

.7296

1.4592

Lye discount 7%

.2128

.8512

1.7024

Lye discount 8%

.2432

.9728

1.9456

Lye discount 9%

.2736

1.0944

2.1888

Lye discount 10%

.304

1.216

2.432

You are seeing lots and lots of decimal places. Always round down for lye because it is always better to have a little less than you need than a little more.

More Excess Oils: Superfatting

You can add oils after the initial saponification in the soap pan to super-fat your soap. Taking a lye discount is actually a way of superfatting, but it reduces the amount of base oils from the outset. When you superfat, you add the oils when the soap is traced, and in theory this is kinder to the oils.

Because you're adding the oils when the soap is traced, you can super-fat with more expensive luxury oils and keep their properties, whereas if you added them at the beginning, they'd become more of the discounted base subjected to the most active lye, thereby losing some of the nutrient value. Whether this is actually what happens is up for debate, but it seems to make sense, so many soapmakers follow this pattern.

A simplified version of this method involves adding 1 tablespoon of superfatting agent per 1 pound of fats. You should do this with a soap formula that already has about 6-percent lye discount, just to be sure. Not every superfatting oil has the same SAP value, of course, but this puts you in a safe range and saves you some math.

You can calculate the combined total lye discount when you create your formula. For example, if you want a total lye discount of 8 percent, you can take a 4-percent lye discount right off the top, and add enough superfatting oils at trace to create another 4-percent discount, bringing the total up to 8 percent.

Going back to our SAP chart, note that a 4-percent lye discount on a 1-pound batch is .1216 ounces. Thus for 16 ounces of coconut oil, use 2.9ounces of lye (3.04–.1216) to achieve a 4-percent discount. To increase the lye discount to 8 percent, superfat with an additional 4 percent oils at trace. So for 16 ounces of oil, add .64 ounces (16 × .04) of superfatting agent.

Sample Oils Batch

Here's an exercise in calculating a soap formula. You can use the formula hypothetically, or you can actually make soap with it. This is an example using what many beginning soapmakers find that they have on hand. Once you've done the math on this one, go ahead and recalculate it for what you actually have.

Let's say you have accumulated small samples of exotic oils and you want to make soap with them for a mixed luxury batch. You have 2-ounce samples of macadamia nut oil, avocado oil, almond oil, jojoba oil, shea butter, and mango butter. You also have on hand your usual olive oil, palm oil, palm kernel oil, coconut oil, and castor oil.

Using the “keep the coconut to a third of the formula” rule, see what you can come up with. You have 12 ounces of fancy oils. For those 12 ounces to equal two-thirds of your total, you will need 6 ounces of coconut oil. That comes to a total of 18 ounces of oils. So this is a “little over 1 pound” batch.

You're going to superfat with castor oil to boost lather, and since you usually use 1 tablespoon of castor oil per pound of fats, you will use a little more than 1 tablespoon. Use 6 ounces of water. Now, you need to calculate the lye. You'll multiply the SAP value of each special oil by two and the coconut by six (to reflect the number of ounces of each). Then, you'll add up all the lye for the complete SAP value of the recipe.

  • Almond oil: 2 × .136 = .272

  • Avocado oil: 2 × .133 = .266

  • Coconut oil: 6 × .19 = 1.14

  • Jojoba oil: 2 × .069 = .138

  • Macadamia nut oil: 2 × .139 = .278

  • Mango butter: 2 × .14 = .28

  • Shea butter: 2 × .128 = .256

Raw lye calculation = 2.63, rounded from 2.616 ounces.

Then, take your lye discount. For this recipe, make it 4 percent, with another 1 percent or so from the tablespoon of castor oil for superfat.

  • 1.6 × .04 = .1052064 ounce discount

  • 1.6-.064 = 1.536, rounded to 1.5 ounces lye

So! Do you feel like a soapmaker? If you've gone this far, it's a good bet you are. If you aren't yet, get busy! Make some soap already!

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