Titrating WVO



For another perspective on this titration see: Biodiesel Titration submitted by MurphysMachines.com.

We titrate WVO to find out how much extra lye we need to add to our biodiesel recipe. That's because the catalyst we use is a base. WVO contains acids like Free Fatty Acids and vinegar that would react with our catalyst, much like baking soda (a base) and vinegar (an acid) react with each other. So, we add extra catalyst so that it can react with the acids in our WVO and still have the right amount left over to act as a catalyst for our biodiesel reaction.

You will need some equipment to perform your titration. You can recycle stuff into a titration station or you can purchase something. For instance you can use baby food jars or you can use chemistry store beakers. Once you understand that you are measuring volumes and weights and know which ones need to be weighed with precision, you should be able to adjust your process to fit your choice of equipment.

There are four steps to the titration:

  1. Making the Alkali Solution
  2. Blanking the Titration
  3. The Titration
  4. Building the Recipe

Step 1 Making the Alkali Solution:

We are going to make a liter of Alkali solution. We only use a few milliliters for a titration so, you only mix up the Alkali Solution one time for many titrations. Your titration solution will start to degrade and need replacing after three months.

When performing your titrations take care not to contaminate your alkali solution by using a intermediate container like a beaker or cup. Pour your solution into the beaker, then draw your titration solution from that beaker to perform the test. This way your titrations will continue to be accurate for up to six months.

Basically we add one gram of the same lye we are using to make our biodiesel to one liter of water. Over time our lye can degrade requiring more to be used to do the same job. If we use the same lye for titration that we use for processing, the titration automatically adjusts for the purity of the extra lye we need to neuralize the acids in our WVO. That makes the solution we mix potentially more accurate than purchasing some already mixed.

It is important that we get as close as possible for accuracy sake. Both when we measure our lye, and when we measure our water we introduce possible concentration errors into our alkali solution. Be sure you use the correct scales and liquid measuring devices for the job.

Step 2 Blanking the Titration:

In this step you will "zero" the titration like you would zero a bathroom scale. Isopropyl Alcohol can get acidic with age and this step corrects for that and prepares the chemicals for the Titration. Many times you will blank with one or two drops. If that is the case, then you can skip this step until you titrate a new batch of oil.


  • The Alkali Solution you made in step 1.
  • Isopropyl Alcohol
  • 10 mL syringe
  • 5mL syringe
  • 4 100mL beakers
  • Indicator solution (phenolphthalein)

Pour 50mL of alkali solution into one of the beakers.


Pour 50mL of Isopropyl Alcohol into a beaker; make sure you don’t mix up the alkali solution and the alcohol


Using the 10mL syringe measure out
10mL of Alcohol into the 3rd beaker



Add three drops of indicator. (phenolphthalein)


Using either the 5mL syringe or the 5mL pipette, Slowly add alkali solution while swirling and mixing the solution until
you get a color change.


Step 3 The Titration

It is a good idea to repeat the titration three to five times and average the results. That way we are more accurate in our titration and in building our recipe.


  • Everything you collected for the blank titration
  • Sample of oil to test
  • A 3mL pipette – the one in the kit graduated to 1mL

1.    Pour 50mL of oil to be tested in the 4th beaker


2.    Using the 3mL pipette add 1mL of oil to the titration beaker. It is critical for accuracy that this be exactly 1mL.


3.    Mix well, you may need to heat in a microwave a couple of seconds if your oil is solid or does not mix well.


4.    Using the same syringe or pipette you used in the blank titration, add alkali solution (keeping track of how much you add) to the titration beaker while mixing or swirling the titration.


5.    Stop adding alkali solution when you get a color change.


6.    You will get a false indication at first, just mix more and the color will go away.


7.    Continue adding alkali solution and mixing until the red stays and does not go away for 15 seconds.

8.    Record the number of milliliters of alkali solution you added to the titration beaker. Do not include what was added in the blank titration. The number of milliliters is your Titration Value.

Step 4 Building the Recipe

There are many different recipes available in the Tutorial under Biodiesel Recipes. Most have two parts. The amount of lye to add as a catalyst, and an amount of lye to add to neutralize the acids. The titration number in milliliters is the result of this test.


Related Links:

Free Fatty Acids Determination in Feedstock for Biodiesel Production - L.S.U. Ag Center Biodiesel Program