Five Biodiesel Tests for Every Homebrewer

1) Testing finished biodiesel for water.

Water in our biodiesel will make it cloudy or turbid. If the biodiesel is clear enough to read a newspaper through a sample then conventional wisdom is that it’s dry enough to use in a vehicle.

The test is temperature dependent since hot biodiesel can hold more water without going cloudy than cold biodiesel. To make sure you have your biodiesel dry enough to use, put it in the refrigerator and chill it down below the coldest temperature your batch of biodiesel is likely to see. If it’s going to be used right away then look to the nightly lows. If it’s going to be stored long term, then look to the historical lows for the period you expect to store it. If the biodiesel gels up before going turbid then you have dry biodiesel.

2) Cloud Point Testing

As biodiesel cools it will start forming crystals of frozen biodiesel. This is different in appearance from wet biodiesel. A little experience at freezing biodiesel will give you the experience to tell the difference. When biodiesel starts to crystallize, it will also start to clog filters, so it’s important to know when to take the gasser and when it’s warm enough to use the diesel. To perform the test stick a thermometer in the biodiesel and check it every so often recording the temperature at which the crystals start forming.

3) The 3/27 Test

This test will give you an indication of how well you converted your WVO into biodiesel. WVO (Triglycerides) will not dissolve in methanol, but biodiesel will. To perform the test, add 3 ml of biodiesel to 27 ml of methanol and swirl it around a bit. Any unreacted oil will quickly fall to the bottom of the methanol. Partially converted biodiesel can fallout as well over time. It will usually fall out in about five minutes, but can take longer.

The ratio of biodiesel and methanol is important. The original test, as reported by Jan Warnqvist on the Journey to Forever web site, used 25ml of biodiesel and 225ml of methanol. The original recipe should be used if you are seeking ASTM level conversions. With less than 25ml of biodiesel your eye may not be able to detect the fallout at near ASTM levels.

Temperature is important with this test. It should be conducted with both the oil and the methanol at or near 70ºF. If either are too hot then you can get a false pass. If either is too cold, you can get a false fail.

4) Testing WVO for Water

This is probably the most overlooked test by beginners, and can cause the most catastrophic problems. It ranks as one of the top 3 reasons behind bad biodiesel. Testing for water is not nearly as difficult as doing a titration on WVO, but it’s the most often skipped test. The bottom line is that with more than 1% water content, it’s nearly impossible to make ASTM quality (conversion levels) Biodiesel. With more than 3% we start running the risk of glop. Glop is a gelatin mass of soap and WVO that plugs up the plumbing and wont drain on it’s own.

Testing for water is not hard. It can be dangerous if you don’t pay attention. The test simply calls for weighing an oil sample, then heating that oil sample to 250ºF and weighing again. The difference in weights is the weight of the water in the original sample. To get the percent water content of the WVO divide weight of the water by the weight of the original sample and multiply by 100.

Now to explain the dangerous part. When the oil reaches 212ºF, the boiling point of water, it can boil violently throwing boiling hot oil dozens of feet in every direction. The water in the bottom of the pan will be pressurized by the weight of the oil on top of it. As we heat it under pressure it becomes superheated. Superheated water only needs a little jar or bump and it all becomes steam in a flash. That sudden expansion of the water under the oil is like a little explosion. It will send the hot oil everywhere. So keep the oil stirred up to prevent water from collecting on the bottom and keep the pan covered when not stirring.

5)Titration Testing WVO

In this test we determine how much catalyst is needed to make a specific batch of WVO into biodiesel. There are actually two reactions taking place when we make biodiesel. The first is that we convert the bad WVO or Free Fatty Acids (FFA) into soap. In this reaction our lye is consumed in the process of making soap. The second and slower reaction is converting good WVO or Triglycerides into biodiesel. For the second reaction our lye acts as a catalyst and is not consumed. We titrate our WVO to find out how much lye will be consumed in the first reaction. That way we can build our recipe with just enough lye to ensure both reactions take place as they should.

Since this test is the one that beginners find the most intimidating, I’ll dedicate a whole post to just how to do a titration in the near future.