Java Fire Log in a Used Paper Coffee Cup




Introduction: Java Fire Log in a Used Paper Coffee Cup

 Java logs are a great product. They use spent coffee grounds and don't require trees to be cut for firewood. According to numerous web resources they also emit less greenhouse gases than burning wood. 

This project is designed to not only use spent coffee grounds but the "disposable" cups we use to have our coffee on the go. As an added bonus it also uses left over candle wax from spent candles and you can even make it in the cup in your microwave with minimal fuss and mess. You can even re-use wooden coffee stir sticks or chopsticks.

This first attempt took about ten minutes to make. I let it cool for about half an hour before I lit it. 

The documentation is from a proof of concept experiment that worked well on the first attempt! 

Step 1: The Materials and Tools

 You will need:

A used coffee cup (Rinsed and dried or even just dried)

Spent coffee grounds, enough to fill a little more than half the cup

Wax, enough to fill about half of the cup, maybe less (It can be from any source, old candles, sealing wax, whatever)

Molasses, a few table spoons worked for me. I suspect brown sugar would also work but didn't try it. (I used unsulphured)  

A knife to chop the wax

A microwave (This shouldn't damage the microwave so proceed without fear)

Optional materials:

A stir stick (I used a bamboo skewer but you could use anything you don't mind covering in wax and coffee grounds) 

A sheet of printer paper, newspaper, a page from an old phone book, any non-glossy paper 

The plastic lid from the cup. I used this for mixing and later to keep the java log from making a mess but it's totally optional.  

Notes on getting the materials:

The cup

I used a basic white 12oz cup. You could use any size that's handy and will fit in your microwave. 

Coffee grounds  

I got my coffee grounds from a coffee shop. Most coffee shops will happily give you more than you can use. Some shops even set out grounds pre-bagged and ready to go so customers can use it in their gardens. You could use grounds from home. It doesn't matter as long as they are dry. 

Espresso grounds from a coffee shop will be pretty dry when you get them. The ones I got were dry enough that I didn't have to bake them or anything before I used them. 


I used leftover wax from a scented candle. I'd recommend using non-scented but just use whatever is laying around. 


I just used some we had in the cupboard. It's cheap and should be the the only material you need to buy. Though I suspect you could use sugar.

There is almost no cost involved in this project.  

Step 2: Optional: Dry Your Coffee Grounds

I didn't do this as the coffee I used was pretty dry but it would probably be a good idea to pop your grounds into an oven safe pan and bake them for for twenty or thirty minutes, however long it takes to dry your coffee if it's still damp. You'll want to keep the oven somewhere around 225 degrees Fahrenheit to avoid cooking the grounds rather than drying them.  

Step 3: Chop the Wax

Just that simple. Put the wax on a cutting board and chop it up. The more fine the better but it doesn't need to be super fine. Just chopped enough to easily mix with coffee grounds.

Be safe and use a sharp knife.  

Step 4: Put the Wax in the Cup and Add Coffee Grounds

This is pretty straight forward. I just filled the cup roughly half way with the chopped wax. I found a few recipes on the web that called for specific measures but when I looked at commercial sawdust fire logs the ratio of wax to sawdust was close to 1 to 1 in favor of the sawdust and decided to go with that instead. My thinking was that dry coffee grounds are fairly similar to sawdust. 

At this point just top off the cup with your coffee grounds and mix. 

I put the plastic lid on mine, plugged the hole with my finger and shook it but it doesn't matter now things get mixed. Just be sure to do it thoroughly. 

Step 5: Microwave It

Simply put the cup and contents into the microwave and nuke it. I used a small low powered oven and two minutes was plenty. It will be hot when you get it out so be careful.  

You will have to figure out what is going to work for whatever microwave you have. 

Note the volume of the wax and coffee mixture will decrease considerably. Mine condensed close to half. 

Step 6: Add Molasses and Stir

All you need to do is add the molasses and stir it. It goes without saying that you must do this while it is hot but I'll say it anyway, 

You must add the molasses and mix while the wax and coffee grounds are hot. 

I added about two or three tablespoons. The molasses is supposed to bind the coffee grounds and keep the wax from just running off and burning too fast. The small amount I added worked but there's plenty of room for experimenting. (I suspect if the grounds are dry enough the wax will saturate them and be OK.)

As noted earlier I also suspect brown sugar would work in place of the molasses and could be added before you microwave the mixture. I'll give it a shot and see at some point. This would be good because sugar is more common and you might not even need to mix the mess after microwaving. Let me know if you try it! 

After the molasses is mixed in, move immediately to the next step without letting it cool. 

Step 7: Possibly Optional: Compress the Mixture

This is where you may want that sheet of paper. I used printer paper to put in the cup between my fingers and the mix but you could just push it down without. 

The important part of compressing the mess a bit is so it cools in a more solid block. If you don't it's likely to crumble too fast while it burns. ...but I could be totally wrong on this. As noted in the next step, compressing might have reduced the surface area of the mixture too much. 

I eventually went as far as to use the molasses bottle on top of the paper to compress the mixture in the cup. 

Pay attention so as not to crush the cup or you'll have a real mess to clean up. The bottle will be a mess anyway. 

Once the block is compressed you're basically done. Now just let it cool and solidify. 

Step 8: Using Your Fire Log

Find a suitable spot like a fire place, fire pit or wood stove. ...or a back yard grill. 

Pull the paper back out of the top of the cup. You can burn it along with the rest but you need the fire to be able to get at the surface of the solid block of wax and coffee grounds. Maybe compressing was a bad idea. 

You may also want to peel apart the seem of the cup but don't remove the paper cup. 

Using a match or lighter set the paper cup on fire. It's probably best to light it so that the flames run up as much surface area of the coffee log as possible. Once the wax melts a little and catches fire it should burn just fine for as much as an hour(or more!). I lit mine in the rain and had to fiddle with it a bit but it worked great. 

I wouldn't recommend cooking directly over one of these on a grill but you could certainly heat a kettle or something and they'd make a great pairing for a DIY camp stove. 

I'll certainly be making more of these for camping and just sitting out back. It'll be a good way to keep disposable cups out of landfills, use a bi-product of my coffee habit, use those spent candles and even enjoy a bit of a fire. Not to mention these are essentially free. 

The last photo was at about and hour and fifteen minutes when I decided to call it a night. 

Have fun and be safe! 

While the point of this project was to make a small portable java log and re-use a paper cup, there is another Instructable that has the recipe pretty dialed in. You can find it here.

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    7 years ago on Introduction

    i made these and put in used, sturdy cup cake holders. I used white sugar because I don't eat it and thought it was a good way to get rid of it. They worked great! My husband was impressed too. I melted the wax in a tin can over a candle warmer - it just took longer to melt the wax. Anyway, thanks for the recipe!


    9 years ago on Introduction

    I wonder if you could pack the grounds into a paper towel tube or an oiled pvc pipe to mold more of a stick that you could use in a rocket stove... Hmmmm... I'm going to have to see what I can come up with....


    10 years ago on Step 2

    Or just put them outside in the sun in the morning and you should be ready to log it up after supper. It's been over 100 far too many days this summer so I could probably be ready by lunch...

    Why didn't I think of this for the Coffee Cup contest? I've made my own java logs before in an old drywall working trough. when It cooled I just turned it out and stacked them on the fireplace.


    Reply 11 years ago on Introduction

    I actually did but by the time I finished it I was on staff and no longer eligible for the contest. Thanks though! I thought it was a good way to keep cups out of the landfill. That and making small, portable, DIY java logs was the idea. That's great that you are making them in numbers like that. It'd be cool to have a stack!


    12 years ago on Introduction

    Something else to consider is that the wax in the microwave is pretty dangerous; if you have a powerful microwave you could wind up with a hot wax fire in it by overcooking, and that could ruin your (day, microwave, house). 

    Best way to melt wax is in a "double boiler"; 1 pot with water, 1 pot inside that pot with the wax in it.  Heat up the water pot and then put the 2nd pot with the wax in it in the water until it melts.  That will ensure you never get a wax fire or have anything nasty happen in your microwave.


    Reply 12 years ago on Introduction

    I was going to make a long reply about the flash point of wax, the inherent dangers of double boilers full of wax on any kind of heating element and the relative safety of any number of things. 

    The web is full of advice, mainly from hobbyists, about how to heat or not heat wax. 

    Pay attention and you'll be fine. Wax only needs to reach about 150F to melt nicely. That happens quickly in a microwave. The flash point of most wax is just under 400F. That's a wide margin for error. Same as popcorn, don't set the microwave for ten minutes and walk away. 

    ...however, in the interests of science! I'll put the word out for a sacrificial microwave and find out just how long it takes to spark a wax fire and then post my findings here. We have a firefighter in the family who will act as our pyrotechnical and safety consultant. 

    Whatever method you use, don't get it overly hot and pay attention to what you are doing. It's wax, it burns, you are using heat hot enough to burn your skin or scald yourself... or even start a house fire.  

    ...and don't take everything you read on the internet at face value. Including this! Do your homework, test some things and find your own vetted experts. 

    If someone else does the microwave test before I do, let me know how it goes! That doesn't mean, tell what you read or heard. I want repeatable results!  :)


    Reply 12 years ago on Introduction

    Well said.  I'd like to see the results of your microwave sacrifice to the Gods of Wax.  Just as an aside, I've done both - wax in microwave and double-boiler.  The microwave works fine; but like you said, I'd never want to walk away from it, and the danger still exists; I've had paper coffee cups blacken around the bottom after less than 00:01:30 in the microwave.

    The double boiler method is very stable and controllable, but likely would be better used if you're making several of these coffee fire cups rather than just one.  Also, use a pot you don't mind getting wax all over - the stuff is a pain to clean out of a good one!

    All the same, I like the *able, gives me something to do with those grounds I generate every morning.


    Reply 12 years ago on Introduction

     Yeah, I asked for mine at a coffee shop and got enough to make a small Java burning man. I'm thankful they took the trouble but I'll need to make a lot of these things to put a dent in that bag. 

    Good point on the larger batches!  


    12 years ago on Introduction

    You might want to add a statement about not burning the plastic lid.  You don't want any environmental people jumping down your throat.  Great 'ible otherwise.


    Reply 12 years ago on Introduction

     Yes, don't burn the lid. It's bad for the environment. ...and if you do, don't breath the fumes, it's bad for your health. 

    It also makes you look bad to the date you are trying to impress with your DIY Java log.