Testing Biochar

Once you have produced charcoal, how do you know if it’s biochar? There are a number of tests that you can do, from seeing how well it absorbs, to seeing how dense it is. As you will see from the following studies, our charcoal performs extremely well when compared with commercial biochar samples, which is why we can use it so effectively for filtering water.

Iodine Test

One of the most common tests done to quantify the filtering capabilities of activated carbon is that of determining the iodine number. This involves stirring a sample of the charcoal in some iodine solution and then doing a titration to determine how much iodine was removed by the sample. 

The pictures opposite give an idea of the filtering capabilities of the samples (the lighter the liquid, the more iodine it absorbed and therefore the better its filtering ability). It also shows how much difference is made by the amount of time the biochar spends in the iodine. 

The full results from our ‘backyard’ iodine number determination can be found here (spoiler – our biochar filtered out more iodine then commercial biochar!)

Samples left in iodine for 30 seconds

Samples left in iodine for 2 days

Key : test-tubes from left to right: commercial activated carbon; commercial biochar; biochar produced in our ‘biocharBBQ’ using apple; oak; pine branches

Filtration Tests

When we first started making these stoves in Kenya, we contacted the Nakuru Defluoridation Company, a company that tests activated carbon for filtering water from the local lakes. 

The results of the tests they ran on our biochar show that, for the first few days, it is extremely effective at removing most dangerous contaminants from the water. The only molecule it failed to remove was fluorine, which is a huge problem in the Lake Bogoria area. This was unsurprising, as the only effective filter they had found for that was bone char! However, their results were hugely encouraging, and their full study can be seen here.

Test your own biochar

We have developed two simple tests so that you can see how well the biochar you have made performs. 

Water Test

You will need some Methylene Blue, which we can supply. If your biochar has been activated, it will remove all the Methylene Blue out of the water, through a process known as ‘adsorption’,


Crush some of your biochar into gravel-size particles.


Find a small jar (about 300ml) and fill it with tap water.


Add 1 drop of Methylene Blue 2% concentration, or two drops of Methylene Blue 1% concentration, to the jar and stir. Pour a small amount into another jar to use as a comparison at the end of your experiment.


Add one tablespoon of your crushed biochar to the test jar and stir. Try and avoid too much charcoal dust.


Leave the jar to stand for 1 hr, stirring occasionally during the first half hour only.


After 1 hr compare the colour of the water in the jars. If your biochar has been well activated it will have adsorbed all the Methylene Blue and the water will be colourless.

You can strain the water from your test jar through a folded sheet of kitchen roll to see just how clear it is.

Smell Test


Crush some of your biochar into gravel-size particles.


Find two glass jars the same size with sealable lids. Place a clove of peeled and sliced garlic into each.


Sprinkle of teaspoonful of your crushed biochar into one of the jars, then seal the lids onto both jars.


The biochar starts to work immediately. Leave the jars sealed for just 5 minutes and then perform a ‘sniff’ test on each. Test again after 20 minutes, again after an hour and again after a whole day. The biochar won’t eliminate the smell entirely, but the reduction should be around 80% after 24hrs.

You can perform the same test with a teaspoon of vinegar in each jar. Banana skins are also a good test.

Join Us

Sign up to become an active part of our project; follow us on social media for frequent updates, and get involved by purchasing your own biocharBBQ.