What are Emulsions?

Search this site!

Emulsions are caused by mixture of two unblendable liquids - in this case, biodiesel and water. Soaps and unreacted fuel aid in creating this mess. There are several methods used to break them, they include settling the mixture for a long period of time, adding salt water, glycerin, hot water, or acid.

What Causes It?

Emulsification can be caused by biodiesel that has not been fully reacted. Fuel that is not fully reacted will contain monoglycerides and diglycerides. In fact, mono and diglycerides are used in the food industry as an emulsifier. They stabilize oil or water hating ingredients. Butter is an example of emulsification used to one's advantage.

Soap in the fuel can also cause an emulsion. Excess soap in the fuel is caused by too much catalyst. Agitation causes the soap molecules to encase the biodiesel molecules and then you must either let it set until it breaks, or use one of the methods mentioned below.

Soaps and unreacted fuel are not the sole cause of this slightly chunky layer. It is the aggravation along with the presence of these substances that causes this inconvenience.

How to Tell if you Have an Emulsion:

• It has been described as looking like Mayonnaise and chicken soup.

• It is most common to have a layer of it between the biodiesel and water layers, although it is possible to have one occur throughout the entire container.

• It will be thicker than water, and may have a hint of yellow to it.

A trouble free batch of pre-washed wvo biodiesel will be a deep brown color (svo will be a slightly cloudy golden color. After the first wash, the biodiesel will lighten slightly in color. The first wash water you drain will be very white, like milk, and will flow just like water.

How to Break an Emulsion:

In order to correct it you should drain the wash water, put the 'chicken soup' in a separate container to settle, and then continue on with processing with the remaining biodiesel. If left to settle, it will usually break within a couple of days, allowing you to remove the biodiesel and finish washing it... or you could try one of these other methods for a faster result:

Heat - heat it up and settle it. Heat decreases the time it takes to break. A great method if you don't want any extra ingredients to remove.


– add hot salt water and it breaks instantly! The heat decreases the density of the oil, while the salt increases the density of the water making them separate easily.

Glycerin – the methanol and glycerin present in the glycerin by-product work to decrease the surface tension of the soap molecules causing it to separate easily from the biodiesel.

Acid – add some vinegar, gently stir it in, and watch as it breaks!

Return from 'Introduction to Emulsions' to 'Biodiesel Homepage'