The 5 Tests Every Home Brewer Should Know


Test 1:

The 3-27 Conversion Test



Homebrewers use the 3-27 conversion test to determine if our biodiesel has completed the chemical reaction from vegetable oil to biodiesel. It is not an ASTM test and does not tell us if we meet ASTM standards. ASTM 5684 is a set of directions used by commercial biodiesel producers to measure the amount of glycerin in biodiesel.

ASTM 5684 specifically tells us four things:

  • The quantity of Free Glycerin in our biodiesel.
  • The quantity of glycerin in our biodiesel that is attached to monoglycerides.
  • The quantity of glycerin in our biodiesel that is attached to diglycerides.
  • The quantity of glycerin in our biodiesel that is attached to triglycerides.

The 3-27 test indicates how soluble our biodiesel is in methanol. Pure biodiesel dissolves completely in methanol without a trace. Pure vegetable oil does not dissolve in methanol at all and forms two distinct phases of methanol and vegetable oil. Monoglycerides and diglycerides partially dissolve in methanol. Unlike pure biodiesel, methanol becomes saturated with monoglycerides and diglycerides at some point and refuse to dissolve more. Methanol becomes saturated with diglycerides more quickly than monoglycerides. So, the 3-27 test is a go/nogo test with a visual indication showing us if our biodiesel has more vegetable oil, diglycerides, and monoglycerides than methanol can absorb. The ASTM test measures the concentration of free glycerin, but our 3-27 test is blind to it since it fully dissolves in methanol.

Monitoring your process: The test can be used in mid process to determine how long to run your reactor, or monitor your conversion at different stages in the process. Not Quantitative: While there must be some relationship between the amount of fallout and the degree of conversion, so far the test is not quantitative. We can’t say that a 1mm bead of oil fallout means “x percent” conversion and if you see a 2mm bead it's twice as impure.


Performing the Test

Add 3ml of biodiesel in a glass container with 27ml of methanol. The methanol must be 20°C (68°F), and the biodiesel must be near that temperature. The methanol must be pure and not recycled or recovered from glycerin.

Mix and let settle for 10 to 15 minutes. Any liquid that settles to the bottom by the end of 15 minutes is a fail. It passes when the biodiesel completely dissolves in the methanol. If it is a little cloudy with no precipitation, that is a pass.

You can perform the test on washed and dried biodiesel, or raw, unwashed biodiesel after you let it settle for a few minutes.


The test is one part biodiesel to nine parts methanol. Increasing the sample size increases the sensitivity of the test. There are references to tests with 10:90, 25:225, 1:9, and others.

The 3/27 test is a qualitative test, meaning a go/nogo test. Some people use it quantitatively as a way to compare one batch to another. However, you should resist the temptation to come up with a formula that converts fallout volume to percent conversion. Those formulas do not work every time for everyone.

There have been tests that compared the results of the 3/27 test to the results of ASTM 5684. If you have a clear and bright sample with no fallout, you are likely to meet or come very close to ASTM specifications for conversion. The two tests do not always agree. However, the 3/27 test is considered by most to be the standard for home-brewed biodiesel.

Related Links:

3/27 and beyond infopop thread

Biopowered Wiki Page on 3/27


Test 2:

WHW Test for Water



The Weigh Heat Weigh test for water in oilWater in the oil is the biggest cause of problems when making biodiesel. Having the dryest oil possible is the biggest key to being able to make quality biodiesel from high titration oils. You cannot assume that just because the oil is clear, that it is water free. As a result, there have been many tests developed to determine water content both qualitatively and quantitatively.

One simple way to test WVO and biodiesel for water content is to use the Weigh / Heat / Weigh method (WHW). It is good for giving quantitative water content measurements down to about 1000-2000 ppm. Below that, you want to use either the Sandy Brae test kit, the Carbide Manometer, or send it off to a lab for the Karl Fisher water test.

You need a good scale, a container for the oil, a microwave, a thermometer, and a stir stick. A triple beam scale is great because it measures up to 2.6kg in increments of 0.1g. A candy thermometer is a good choice, anything that measures the temperature up to about 125°C (260°F). If you use a microwave, a plastic container is sufficient for the task. If you use a hot plate, a saucepan for your container is a better choice. I have and use a hot plate stirrer with a pyrex beaker.

warningNow to explain the dangerous part. As we heat the oil, beads of water settle to the bottom of the container. The weight of the oil on top of the water pressurizes the water in the bottom of the pan. The added pressure on the water raises its boiling point a little, becoming superheated. The superheated water only needs a little jar or bump to release the pressure, and it all becomes steam in a flash. That sudden expansion of the water under the oil is like a little explosion. It throws the hot oil everywhere. To prevent the water on the bottom of the container from becoming superheated, stir the oil vigorously as it approaches the boiling point of water.

The procedure:

Weigh your container and record the weight as the tare weight.

Add WVO to the container, about 1kg and record the weight as the wet weight.

Heat the oil to above 120C STIRRING constantly.

Weigh again and record the weight as the dry weight.

The calculation:

Subtract the dry weight from the wet weight and record as the water weight.

Subtract the tare weight from the wet weight and record as the oil weight.

Divide the oil weight into the water weight and multiply by 100 for the percent water content.


Empty beaker weighs 150g for tare weight

Beaker plus oil weighs 1150g for wet weight

Beaker plus dry oil weighs 980g for dry weight

Water weight = 1150g - 1127g = 23g

Oil weight = 1150g - 150g = 1000g

Percent water content = 23 / 1000 x 100 = 2.3%

Convert Percent Water Content to ppm:

ppm = percent water content x 10,000

In the example 2.3% = 23,000 ppm


Test 3:

Cloud Point and Pour Point Tests



Gel point and cloud point test for biodiesel

When it gets really cold, biodiesel can start to gel up, plugging fuel filters. The temperature where this happens is called the Cold Filter Plugging Point (CFPP). This temperature varies depending on the properties of the oil and the processes used to make biodiesel. Unfortunately, CFPP is nearly impossible for biodiesel hobbyists to determine at home. You can send your biodiesel off to have it tested, but this can get expensive. So, there are two tests that we use to help estimate the lowest temperature we can use our biodiesel. These two are testing for Cloud Point (CP) and Pour Point (PP).

Cloud Point is the temperature at which the crystals of solid biodiesel first become visible. As the biodiesel starts to freeze, it forms small crystals that start clumping together. They become visible as cloudy biodiesel when they grow to four times larger than the wavelength of visible light. At this size, the crystals easily pass through filters and can be pumped and used with no problems. At colder temperatures, the crystals grow to the point that they plug filters.

Pour Point, or Gel Point as home brewers call it, is the temperature where biodiesel becomes solid and no longer flows. Once your biodiesel reaches the pour point temperature, it is well past the Cold Filter Plug Point, making Cloud Point the most important temperature for cold weather biodiesel.

To measure the Cloud Point and Gel Point of your biodiesel, put a sample in your refrigerator. I use a mason jar with a plastic lid, through which I stick a thermometer to measure the temperature as it cools down. You want to try to inspect it at 1C increments for cloud point. If the biodiesel does not gel up in the refrigerator, move it to the freezer and continue checking it on a regular basis until it gels up.

Most of your biodiesel made from the same oil source has similar cloud and pour points. So, most hobbyists do not test every batch. Instead, we put a quart to a gallon of the same fuel we have in our tank in a glass jar and set it next to our vehicle. Inspect it in the morning to see if it reached either the cloud point or pour point.


 Related Links:

Biodiesel Cloud Point and Cold Weather Issues -  


Test 4:

Testing Methanol for Purity



Over time methanol absorbs water from the air. Each time you open a container of methanol, it absorbs a little water. If you have a drum of methanol with a pump installed in the bung, normal heating and cooling forces air in and out of the drum. That air contains water until the methanol absorbs it. Water in our methanol can cause problems for us when we make biodiesel. That is why it is important to have a test that checks the purity of our methanol.


We do not use this test very often unless you recover your methanol. However, it is useful to check your methanol purity to determine the cause of a bad batch. If suddenly you made a lot more soap than normal, then check your methanol for purity. Less than 95% purity can cause you problems. Remember your oil also has water in it and these two combine to make your water contamination worse.

The simplest way to check for purity is to measure its specific gravity. Specific gravity is the ratio of a substance's density to the density of water. If a liquid is lighter than water, it has a specific gravity of less than 1.0. Substances with a specific gravity greater than 1.0 are heavier than water. Density is the mass of a substance divided by its volume. As we know, things expand when heated and shrink when cooled, so density, and therefore specific gravity is temperature sensitive. So, to be accurate in our readings, we must record the temperature of the methanol when we measure specific gravity.

The tool for checking specific gravity is called a hydrometer. It is a weighted glass tube that floats in the methanol. Specific gravity is determined by how deep the glass tube sinks in the methanol. The specific gravity is read directly off a scale in the glass tube. There are three scales commonly used for checking the purity of methanol.

  • Specific Gravity
  • Tralles
  • Proof

The specific gravity scale reads directly in specific gravity. The specific gravity of pure methanol at 20°C is .7913. As our methanol absorbs water, its specific gravity increases, reaching a maximum of 1.000 at 20°C. If we have a specific gravity of .8957, then we have a solution of half water and half methanol since .8957 is halfway between .7913 and 1.000. That leads to the formula of:

    Methanol Purity = (1 - specific gravity) divided by 0.2087

To adjust for temperature, we need to use the chart below. Find your measured specific gravity on the left-hand column and the measured temperature in °F along the top. Find the spot in the chart that is under your temp and to the right of your specific gravity and read the number as percent methanol.

methanol density chart for hydrometers calibrated at 15C

Hydrometers are designed to operate over a limited range of specific gravities. The narrower the range, the more accurate the reading. Distillers and wineries use special "tax certified" hydrometers that have very small ranges. General purpose hydrometers like one that ranges from 0.7000 to 1.000 work for determining the purity of methanol, but they are not very precise particularly near 100% pure. With general purpose hydrometers, it is possible to end up with a reading of 110% pure, particularly if the temperature is not factored in.

Another scale used in hydrometers is the Tralles scale. It is a scale used when measuring the purity of Ethanol. Methanol and Ethanol both have very similar densities letting us use a hydrometer marked in the Tralles scale. It is reading percent methanol content directly. A reading of 100 is 100% pure ethanol. A reading of 0 is 100% pure water. Hydrometers using the Tralles scale are available in most winemaking hobby shops with a range from 0 to 100.

Another Alcohol scale is the Proof Scale. It is exactly two times the Tralles scale. 200 proof would be 100% alcohol. It is the scale used to measure liquor.

If you do not have a hydrometer, you can still roughly measure the purity of your methanol. You need the labware to measure 1 liter accurately, and a scale capable of measuring to a tenth of a gram. Certified glass graduated cylinders, and volumetric flasks are both good ways to measure out exactly one liter. Be sure you subtract out the weight of your container. Just like with a hydrometer you must adjust for temperature before determining your percent methanol. Find the mass in kilograms of one liter of methanol and use that for specific gravity in the chart above.

Related Articles


Methanol for Biodiesel

Methanol or wood grain alcohol is the simplest form of alcohol. It is both poisonous and flammable. It is used in racing, making it available at both chemical supply houses and fuel distributors. It burns without a visible flame in bright sunlight, and it is the most expensive ingredient for most homebrewers.



Biodiesel Safety Tips

Top 10 Safety Tips

Over the years there have been a number of biodiesel processing related accidents and fires, even some serious injuries and a couple of deaths. Making biodiesel is inherently dangerous. Here are 10 basic safety tips that can help reduce your exposure to accidents and fires.




MSDS for Biodiesel

A Material Safety Data Sheet (MSDS) is a document that contains information on the potential health effects of exposure to potentially dangerous chemicals, and on safe working procedures users should adhere to when handling chemical products. Download your own MSDS for the chemicals you use to make biodiesel.



Related Links

Infopop Thread on Hydrometer Accuracy

How To Use A Hydrometer

Test 5:


Titrating WVO

Titrating WVO is essential to understanding the quality of your oil. It is a simple test and is used to build a biodiesel recipe. This article contains instructions and videos on how to titrate.