Kopi Joss, Charcoal Coffee
Kopi jossKO-pee joss
A glowing ember of hardwood charcoal dropped straight into a glass of sweet black coffee. It hisses, throws up a cloud of steam, and leaves the coffee smoother and faintly of woodsmoke.
At a glance
- Coffee : water
- 1:10
- Active time
- 5 min
- Total time
- 20 min
- Makes
- 1 glass
- Serve
- Hot, ember in
- Kit
- Charcoal + tongs
Ingredients
Note: Use natural lump hardwood charcoal and nothing else. Briquettes contain binders, accelerants and sometimes borax, none of which belong in a drink.
Method
-
Get the charcoal properly glowing
Light a lump of natural hardwood charcoal and let it burn until it is glowing orange all the way through, with no black patches and no smoke coming off it. That takes ten to fifteen minutes on a grill or over a gas flame with tongs.
A half-lit lump is the one thing that will ruin this. Unburnt charcoal still holds volatile compounds, and those are what taste acrid.
Burn 10 to 15 minutes -
Brew it tubruk style
Put the grounds and the sugar straight into a thick, heatproof glass and pour the hot water over them. No filter. Stir once and let it stand for four minutes while the grounds settle to the bottom.
Settle 4 minutes -
Drop the ember in
Take the glass outside or stand over a sink. Grip the glowing lump with long tongs, knock any loose ash off it, and lower it into the coffee. It hisses hard and throws up steam, which is where the name comes from.
Leave it in for thirty seconds or so, then lift it out, or leave it sitting in the glass as the street stalls do.
In the glass 30 seconds -
Let it settle, then drink around the grounds
Give it a minute. The grounds sit at the bottom with the ash, and you drink from the top without stirring. Stop before the last mouthful.
Why this works
Charcoal is almost pure carbon with a huge internal surface area, and carbon adsorbs organic molecules. That is the same property that makes activated carbon work in a water filter. Drop a lump into coffee and some of the acids and bitter phenolics bind to its surface and come out with it, which is why the cup tastes rounder and less sharp afterwards. The effect is real but modest: this is a lump of grill charcoal for thirty seconds, not a filtration system.
The second effect is pH. Wood ash is alkaline, and a little of it inevitably goes in with the ember, which nudges the coffee's acidity down. Indonesian robusta brewed tubruk style is already low in acid and heavy in body, so the result reads as unusually smooth.
The third is simply heat and smoke. A glowing ember is somewhere around 600°C, so the moment it enters the liquid it flash-boils the coffee immediately around it. That violent local boiling is the joss, the hiss the drink is named for, and it drives a little woodsmoke into the cup along with it.
It was invented at an angkringan, a low street cart, near Tugu station in Yogyakarta in the 1960s, and the story told there is that it started as a folk remedy for a cold stomach. Whether or not that holds up, the stalls are still there and still doing it the same way.
One honest caveat. People will tell you the charcoal detoxifies the coffee or makes it healthier. There is no good evidence for that, and swallowing ash is not something to aim for. Make it because it is spectacular and because it genuinely tastes different, not because it is good for you.
Variations
- Kopi joss susu: a spoon of condensed milk stirred in before the ember.
- With ginger: a few slices of bruised ginger in the glass with the grounds.
- Less sweet: Yogyakarta makes it sweeter than most visitors expect. One teaspoon is a reasonable Western starting point.
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Questions
Is it safe to drink?
With fully burnt natural hardwood charcoal, yes, and it has been street food in Yogyakarta for sixty years. Never use briquettes, which contain binders and accelerants, and never use a lump that is still smoking, because that means unburnt volatiles are still coming off it.
Does the charcoal taste of anything?
Faintly of woodsmoke, and the coffee tastes noticeably less sharp. If it tastes acrid or ashy, the charcoal was not fully lit before it went in.
Can I use activated charcoal powder instead?
It is not the same drink. Powder gives you grey coffee with no smoke and no hiss, and it can bind to medication in your stomach. The ember is the entire point.
Will the glass crack?
Use a thick heatproof glass and make sure the coffee is already hot. Dropping a 600°C ember into a cold thin glass is how you find out why the stalls use heavy ones.
Do I leave the charcoal in?
The stalls leave it. Thirty seconds is enough for the effect, so lift it out if you would rather, and either way do not drink the last mouthful.