The Knice-N-Clean Glycerin SAP Test

The Knice-N-Clean Glycerin SAP Test (KNC SAP Test)
by Rick Knicely of Knice-N-Clean Soap Company LLC

Determining a SAP value for your biodiesel glycerin (BDG) is a simple process that will make BDG soaping  easier and more consistent. Everyone’s BDG can be a bit different, however if you maintain the same oil sources and processing methods, your BDG SAP should remain somewhat consistent.

Armed with the proper SAP value for your BDG will allow you to be sure that all of your saponifiable elements have been turned into soap. Without a proper SAP value your soap can come out caustic hot or become rancid over time. A proper SAP value will also ensure that your soaps are not superfatted with saponifiable elements such as biodiesel. Undersaponified liquid soaps can be cloudy. However, liquid and gel soaps made with a proper SAP value will turn out crystal clear.

First you must be sure your BDG has had the methanol removed, preferably with a distillation method and the your BDG is as dry as possible.  We heat our BDG up to between 275ºF and 300ºF or until the BDG just starts to smoke.  This ensures that our BDG is dry and as free of methanol as possible.

Calculating a SAP value is similar to performing a titration. You will take a known amount of BDG and add iterations of a caustic solution until you have fully saponified any saponifiable elements left in the BDG. Summing the iterations used will result in a SAP number.

It is possible that you could have a negative SAP value.  This can happen when you have excess caustic left over after your boidiesel reaction.  I will refer to a positive SAP as +SAP and a negative SAP as -SAP for the remainder of this post.

After a SAP value has been determined using  KNC SAP Test not only can you be sure that your BDG soap is fully saponified but you can also can use your BDG as an ingredient in any soap recipe.

The SAP Solutions
The caustic solution is created by dissolving either NaOH or KOH into distilled water.

Bar (NaOH) SAP Solution

• 1000g (1 liter) of distilled water
• 140g of NaOH

Liquid/Gel (KOH) SAP Solution

• 1000g (1 liter) of distilled water
• 200g of KOH

Negative SAP Solution

• 1000g (1 liter) of distilled water
• 232g of Citric Acid

Check for a -SAP
If the pH of your BDG is 11 or greater you most likely have a -SAP.  If this is the case follow the instructions below on "Determining Your -SAP Value" otherwise continue with "Determining Your +SAP Value"

Determining Your +SAP Value

1. Start by selecting a starting SAP number. A 20% SAP number is a good starting point. Once you have an idea of your BDG SAP you can better predict your starting SAP number for future KNC SAP Tests.
2. Measure out 200g of distilled water into a wide mouth mason jar or other microwave suitable container.
3. Add 100g of BDG to the distilled water.
4. Stir until the BDG is fully dissolved into the distilled water.  Mixing with a stick blender will greatly reduce the time needed to perform the KNC SAP Test.
5. Place the jar in the microwave and using short 15-30 second bursts heat the solution until the temperature reaches 213ºF or you notice the solution coming to a small boil.  Note: Re-heat the solution as necessary to maintain 213ºF.
6. Measure out the starting amount of the +SAP solution. If your starting SAP number will be 20% you will add 20ml of your SAP solution to the BDG solution. Mix well preferably with your stick blender.
7. Place the jar back into your microwave using short 15-30 second bursts until you notice the solution starting to boil. Watch carefully because this may create a lot of foam and could spill over the top of your container.
8. Check the pH of the BDG solution. The pH might be quite high at 12 or above. You should then notice the pH start to drop. This can occur as fast as a few moments or take long as an hour.  During this time try to maintain a temperature above 190ºF.
9. Once the pH has dropped to or below 10.5 add 1ml of the +SAP solution. Keep track of how many ml you have added.
10. Continue with steps 8 and 9 until the pH is at or above 11 and the pH does not drop for at least an hour. At this point you have fully saponified any saponifable elements left in the byproduct.
11. Add the SAP starting value and the iterations of +SAP solution together then subtract 1. By subtracting 1 you are not including the 1ml that caused the pH to remain above 10.5.
12. For this example lets assume your starting SAP number was 20% and you added 5ml of SAP solution. The math would be (20 + 5 - 1) or a SAP number of 24%.
13. Use the Knice-N-Clean Soap Calculator to create a soap recipe from your BDG. Simply select "Glycerin Byproduct (BDG)" from the ingredients drop down. Enter the amount of BDG you are going to use. Then select your SAP number from the SAP dropdown. The calculator will then indicate the amount of caustic you will need to saponify your BDG and other ingredients you select.
14. The Knice-N-Clean Soap Calculator will also allow you select other soap making ingredients you may want to use along with your BDG. Again the calculator will take care of all the SAP math and totals for you.

Determining Your  -SAP Value

1. You will be starting out with a -1% SAP number. Each -1% is 1ml of negative SAP solution.
2. Measure out 200g of distilled water into a wide mouth mason jar or other microwave suitable container.
3. Add 100g of BDG to the distilled water.
4. Stir until the BDG is fully dissolved into the distilled water.  Mixing with a stick blender will greatly reduce the time needed to perform the KNC SAP Test.
5. Place the jar in the microwave and using short 15-30 second bursts heat the solution until the temperature reaches 213ºF or you notice the solution coming to a small boil.  Note: Re-heat the solution as necessary to maintain 213ºF.
6. You will be starting with a -1% SAP. Measure out 1ml of the negative SAP solution and add it to the to the BDG solution. Mix well preferably with your stick blender.
7. Place the jar back into your microwave using short 15-30 second bursts until you notice the solution starting to boil. Watch carefully because this may create a lot of foam and could spill over the top of your container.
8. You should notice the pH start to drop quickly, much quicker than you see when testing for a +SAP.   Check the pH of the BDG solution.  During this time try to maintain a temperature above 190ºF.
9. If the pH is still above 10 add 1ml of the -SAP solution. Keep track of how many ml you have added.
10. Continue with steps 8 and 9 until the pH is at or below 10. At this point you have fully neutralized any caustic left in the byproduct.
11. Add the iterations of  the -SAP solution together then add 1. By adding 1 you are not including the 1ml that caused the pH to remain below 10.5.
12. For this example lets assume you used 5ml of  the -SAP solution. The math would be (-5 + 1) or a SAP number of -4%.
13. This means you will need to use a whole oil or fatty acid in your recipe to make up for the -SAP value.
14. Use the Knice-N-Clean Soap Calculator to create a soap recipe from your BDG. Simply select "Glycerin Byproduct (BDG)" from the ingredients drop down. Enter the amount of BDG you are going to use. Then select your SAP number from the SAP dropdown. The calculator will then indicate the amount of caustic you will need to saponify your BDG and other ingredients you select.
15. The Knice-N-Clean Soap Calculator will also allow you select other soap making ingredients you may want to use along with your BDG. Again the calculator will take care of all the SAP math and totals for you.

Multi Jar Variation

1. Prepare 4-6 jars using steps 2 thru 5.
2. Add 14ml of SAP solution to the first jar.
3. Increase the SAP solution by 2ml for each of the other jars. i.e. 14ml, 16ml, 18ml, 20ml, 22ml, 24ml.
4. Mix each jar with your stick blender.
5. Place all of the jars into an oven or roaster with the temperature set at 205ºF.
6. Allow the jars to "cook" for 2 hours.
7. At the end of 2 hours check the jar with the highest SAP test. If the pH of the solution is 10.5 or below you will need to add more solution to each of the jars and follow step 6 and 7 again. Add enough SAP solution to the first jar to make it 2ml more than the last jar. Again increase the SAP solution by 2ml for each of the other jars. i.e. 26ml, 28ml, 30ml, 32ml, 34ml, 36ml. Note: If the pH of your first jar is over 10.5 you will have to start out with a fresh set of jars. i.e. 2ml, 4ml, 6ml, 8ml, 10ml, 12ml.
8. Find the jar for which the pH of the solution is closest to 10.5. The SAP number for that jar is the SAP you can use for your BDG with the Knice-N-Clean Soap Calculator.

Note: (-SAP Multi Jar): If you are using the Multi Jar method in determining a -SAP value, for step 3 you can start with 1ml of -SAP solution and then increase by 1ml for each jar.  i.e. 1ml, 2ml, 3ml, 4ml, 5ml. And  for step 7 you will check for a pH of 10.  If you have to continue to another set of jars you will start with 6ml and go up by 1ml. i.e. 6ml, 7ml, 8ml, 9ml, 10ml.

Note: You can also use your stove top when performing the KNC SAP Test. To do this use a steel or glass pan and keep the temperature at or just above 213ºF for the duration of the test. Add distilled water as necessary to replace any water that might boil off during the test.

YOUR BDG MUST NOT CONTAIN METHANOL WHEN PERFORMING THE KNC SAP TEST.

DO NOT USE AN ALUMINUM PAN FOR THE KNC SAP TEST.

Helpful Tip: Fill a full 55 gallon drum or 275 gallon tote with your BDG. This way 1 KNC SAP Test will be valid for a much larger volume of BDG!

To  learn more about soap making from Biodiesel glycerin, be sure to check out our great book "Making Biodiesel Glycerin Soaps". It contains this SAP test method and many more great tips & tricks for getting the best soap out of your Biodiesel glycerin. Click here to learn more.

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