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
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)
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:
I used a basic white 12oz cup. You could use any size that's handy and will fit in your microwave.
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
Step 3: Chop the Wax
Be safe and use a sharp knife.
Step 4: Put the Wax in the Cup and Add Coffee Grounds
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
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
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
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
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.