Umikari, or burnt rice husk tooth powder

How did you brush your teeth growing up? Many of us in the rice growing states of India will have memories of dabbas filled with a black siliceous powder, mixed with salt, maybe camphor, maybe some cloves or cinnamon for mouth-freshening effects–taking little spoonfuls of this, applying it on teeth with fingers and rubbing gums, often not in a bathroom but near a well or water pump in the early mornings and grinning and laughing with cousins or siblings these wide-mouthed white-and-black toothy grins, under the supervision of a preoccupied parent or aunt or in the company of an indulgent grandparent marshalling these playful messy-faced children through their morning ablutions.

The branded tooth powders all came later: Monkey brand, Vicco, Dabur. Before all those & in the beginning, there was umikari.

My work with heritage rices & Shalikuta has taken me in all sorts of directions through rice economies–lives, recipes, caring for soil, medicinal practices, and waste–which reframe my own little memories of growing up in rice countries, connecting big to little. Umikari is burned rice husk, and rice husk (or “umi”) is one of those excesses of rice farming, a little like cottonseed but by product of stunning proportions. Rice husk doesn’t make a great cooking fuel thanks to its high silica content, and its household uses are limited though clearly not non-existent. So it is largely waste to be burned the way much waste is burned (sometimes harnessed in small scale power generation), and its story is largely one of industrial salvaging because of the sheer scale of its (by-)production.

The big story of rice husk waste in short form

Of the 120-odd million tonnes of paddy produced annually, 24 million tonnes is rice husk (RH). (Paddy stubble and stubble burning causing significant drops in air quality is another major issue, which I’m not addressing here.) The industrial uses of RH agro-waste are thankfully many: “in brick kilns [and for making bricks], furnaces, in parboiling process of rice, the raw material for the production of sodium silicate, as an cleaning or polishing agent in metal and machine industry” and so on [Source; the IRRI has also a good overview.]

Now RH is about 20% of the weight of paddy, and, when burned, it reduces to rice husk ash (RHA) which is about 25% in weight of the husk. If rice husk is used as a fuel source, as is often the case with parboiling, in small scale power generation & many other uses listed above, then RHA is a natural byproduct. This means that RHA is still several million tonnes of a waste byproduct derived from rice production which has researchers scrambling to identify suitable uses. “Green building” advocates have often turned to RHA for its pozzolanic qualities–which means that RHA belongs in a category of siliceous materials, which can be used (in the presence of water and calcium hydroxide) to produce cementitious compounds that then become useful in brick-making, house-building and so on. RHA is a component of white Portland cement, which Indians know as “JK White.” It’s also used in natural rubber vulcanization, soil amelioration, and so on.

The much smaller, household scale story is not unconnected from all of the above in the sense that rice husk waste is a personal concern for individual farmers as well. & it’s possible that the use of husk as a fuel source for parboiling, as a soil additive and garden mulch, and even husk-for-bricks originated in these contexts first. Same with RHA (which is locally known as sambal), but the use of charred rice husk or umikari for tooth and oral care is very much an artifact of the small scale rural economy, which has stayed pretty much so and never scaled up.

Umikari is not activated charcoal

Here’s where terminologies start to get loose & need some realigning. Rice husk is always rice husk, but RHA for industrial uses does have to be produced by controlled burns to ensure certain particle sizes which then make it more suitable for the production of cementitious compounds. At the household level, the fine biochar produced from paddy husk is simply umikari, and the ash is sambal.

Now google “umikari” and you’ll come upon a hundred links that promise activated charcoal–whose benefits and values many many will extol (soil improvement, water filtration, hair cleansing, face cleansing, odour reducing and on and on). But home-made umikari is not usually activated charcoal at all & you have to know the difference.

Strictly speaking, umikari is just burned on a stove-top (for smaller quantities) or outdoors (for larger amounts). It is burned until powdery (which is why it is also sometimes used interchangeably with sambal) and not treated in any other way.

Activated charcoal, by contrast, is produced via high temperature (800-1000C) controlled burns and steam treatment, or chemically with the use of chloride salts and/or oxidizing gases. Steam activation produces the best results overall, but the method chosen depends generally on the carbon source, the available infrastructure, and the desired end-product (chemical activation only produces powders, for instance). The end result is a carbon with a more-or-less porous structure that allows for vastly improved adsorption. The porous structure of activated charcoal is said to open up so much surface area that 50g can have the surface area of 17X football fields–hence all its incredible touted cleansing, detoxifying properties! [Read more about the activation process here.]

Net-net, buyer beware: umikari ≠ activated charcoal. Or is most unlikely to be activated charcoal, or is most unlikely to be activated charcoal of the required quality to work its magic in your mouth. All of which suggests that umikari in tooth powder is being used much more for its abrasive qualities (thanks to high silica content), and not so much for its adsorptive qualities. Which seems a shame, since activation improves cleansing!

Making your own activated charcoal

Now it appears not-too-hard to activate your own charcoal at home. There are a few DIY guides out there [such as this one] and they typically call for the use of calcium chloride or zinc chloride. One 2012 study I found by a Santa Clara University group claims that a low-cost, simple strategy for the developing world could replace CaCl₂/ZnCl₂ with simple table salt, NaCl–but that further testing would need to be conducted to really compare CaCl₂/ZnCl₂-activation to NaCl activation. For now, we can say that NaCl activation does improve adsorption, but we’re not sure precisely by how much [Source: Ami Cobb et. al., “Low-Tech Coconut Shell Activated Charcoal Production,” International Journal for Service Learning in Engineering, Vol. 7(1), pp. 93-104, Spring 2012].

The other natural, readily available ingredient to use for activating carbon is lemon or lime juice–replicating, one presumes, the “acid wash” effect of chemical activation (which is sometimes used as an additional purifying step in steam activation). The trouble with these home-methods is that there’s no quantitative way to test them easily. Even the Santa Clara group used a “visual colorimetric method using a common dye indicator (methyl orange) as a proxy chemical for pesticides and herbicides” while in the field–which is to say that they placed the activated carbon in a jar with methyl orange (a soluble organic dye) and watched to see if the color intensity decreases. Color decreased with NaCl activated carbon, and didn’t with inactivated carbon. That confirms that NaCl activation is happening, but it’s all visual, subjective, and qualitative data.

But if you trust the process, and aren’t concerned about making any great claims about the superior quality of your activated carbon or your carbon shampoo over any other — then there’s no harm in trying it.

Which is what I did. Lemon/lime “acid wash” activation is likely better since this umikari is for oral use anyway.

So let’s backtrack through the whole process of making umikari, activating it, and then converting it into that toothpowder of our rustic pasts and our urban adult nostalgia.

Step 1: Burning rice husk or umi, or pyrolysis (mostly)

I should admit right off that unless you live on a rice farm or close to one, simply obtaining rice husk can be a challenge–for all its overabundance. I found a bag right at harvesting season from Annapurna farms in Auroville (thanks to Nitin and Tomas).

There are two ways to burn the husk, after you have it in hand.

The stovetop method

The first is on a stovetop, the way this was done in village homes. The method has the bonus of also serving to season new clay cookware.

Here you essentially take a small quantity of rice husk and heat it slowly until it smokes, mixing all the while to get an even burn. It might even catch fire–so you should only do this if you have good ventilation, and a kitchen without flammable walls! In the villages, the fire-in-the-pot was kept in check with a banana or other leaf, and then the charred umi cooled–powdered–mixed with salt–used.

Here’s how I did it, mixing constantly, but not allowing the rice husk to burn in the pot itself. I stopped and re-started a couple of times; the process is pretty forgiving.

The chimney method

To increase the quantum of rice husk burnt for use in soil amelioration, or for filtration means you’ll need to take the process outdoors, and create a makeshift chimney. This is easy: simply roll up a sheet of metal and knock holes in it with a fat nail for ventilation. Set the chimney upright on a stable brick or other surface (I used just the pan that masons use here to mix cement). Fill the base of the chimney with charcoal and other combustibles that will burn slowly and at high temperatures. Gather the rice husk around this chimney & mix occasionally as the heat increases and the husk chars.

Here’s the view in images:

& here it is in a video:

This carbonization process with an outdoor chimney is probably more efficient in dehydration and de-volatilization than the stovetop method above because it likely reaches higher temperatures. It’s also much less risky as it’s all done outdoors. So, using this method you could produce rice husk biochar for oral care, those face masks of your dreams, and basic water filtration, soil improvement and so on (though not for hydroponics).

Once you have a well-charred rice husk that turns to powder on its own or with the slightest rubbing, let it cool. Sieve this a few times to get rid of the bigger particles remaining, and until you have a fine, reasonably consistent biochar powder. Note: This step is important because you really don’t want to be scrubbing your teeth with large, abrasive particles! The finer the powder, the better the umikari quality, the more effective the activation, and the safer your tooth enamel will be.

Step 2: Activation with lemon juice

Weigh your umikari. Using a rough 100g:100ml ratio, you’ll want to get the right volume of lemon juice.

Note: that I arrived at this by watching a couple of videos, none of which were terribly precise on the weight to volume ratios required for activation. In the absence of any testing, this is proceeding on trust (for now) & the belief that some activation is better than no activation at all!

Transfer the umikari to a glass jar and pour the lemon juice over it. Mix with a spoon or just close and shake the jar so you get a slurry. Make sure the lime/lemon juice covers the umikari; add a little water if necessary to get it submerged.

Leave this for 24 hours, shaking every now and again to hydrate the umikari that settles below.

After 24 hours, drain the lime juice out using a fine-meshed strainer. You’ll now need to wash the activated umikari a few times to remove all traces of the activator. The recommendation here is to use distilled water or pure H₂O which is used for vehicle batteries and such like (so is available at gas stations in India). Regular water will have impurities and even fluoride which will be absorbed by the activated charcoal, reducing its efficacy. Rinse the activated charcoal out 3 times.

Spread it in a baking tray & set it in the oven at lowish temperature or just out in the hot sun to dry completely. Bottle this and store.

Step 3: Making umikari pallu-podi, or tooth powder

This is the easiest step. For each 100g of activated umikari, add:

• about 1 teaspoon of table salt, antiseptic and anti-bacterial
• a generous pinch of powdered cloves and/or cinnamon, mouth freshening (optional)
• a generous pinch of powdered edible camphor, mouth-freshening and anti-bacterial/anti-fungal (optional)

Bottle and store.

Step 4: Cleaning your teeth

To use, take a little of the umikari mix in the palm of your left hand. Wet your right pointing finger and dip in the powder. Rub this over your gums, getting into corners as best you can. Rinse and wash off.

Remember that rice husk is high in silica–so it’s great for getting out plaque, but it can also strip tooth enamel. I use this about once a week, just to be safe. I also have added it to a portion of a more complex tooth powder, which I’ll blog next–but I use the tooth powder mix with umikari also just about once a week. Not more.

When I do use it though, it leaves my teeth feeling squeaky clean. Of course I’ll never know how much that owes to the gum massaging that comes with such non-toothbrush-oriented practices versus the umikari itself. But really, who cares? I never feel the same after using toothpaste, with fingers or with a toothbrush. In that sense, umikari just rules & is worth all the effort it takes to make it.

Coming next: this full-fledged tooth powder, garam masala for your teeth! Stay tuned…