This intructable should give you a general idea of how to maintain your vermicomposting system, aka worm bin. I will go over how to balance food, bedding, water, and air in the bin, as well as how to separate out the worms and finished worm manure from the intact garbage.
This information is meant to be used for a "traditional" plastic or wooden box. If I were to build another worm bin, it would be of the "Worm Bag" type. Most of the information came from Mary Appelhof's book Worms Eat My Garbage.
Step 1: A Word About Bin Designs
There are many varieties of worm bin designs, but my favorite is the indoor worm bag design. I made my own before I'd seen that design, so until I get a big increase in the amount of food waste my house produces, I don't think I'll make another one.
My bin is just a plastic storage bin with some air and water vents added. The main vent is a length of thin-walled PVC pipe that runs the length of the bin. I first drilled small holes along the pipe, then cut holes on either end of the bin with a pocket knife. The pipe is held in place with Gorilla Glue. There are also some smaller vents at the top of the bin that were there when I got it
Where you see the red electrical tape is where I tried putting window screen over the vents to keep flies out. It worked for the most part, but some of the smaller flies were still able to get in and out.
You can also see my backyard compost pile, which sits in the corner of my chain-link fence. It's not much more than a pile, although I have piled up some lumber on the third side, and added some window screen to keep mice from burrowing into the pile.
I've made this into somewhat of a "worm bin annex," adding worms to the pile, and putting compost into the worm bin to be finished.
Step 2: Lay Out a Tarp and Put Some Gloves On
This is going to get messy, so I suggest using some plastic or rubber gloves.
The tarp is mostly just to provide a clean flat surface to work on, so a concrete floor would work just as well.
You might also want some garden tools like a shovel or tilling fork, but I used my hands for most of the work.
Step 3: Open the Bin, and Start Pulling Stuff Off the Top
On top of the worm bin, there will be all the food scraps that the worms haven't eaten yet. Pull this off and set it in a pile.
At the bottom of this layer (and the top of the next), most of your worms will be hanging out. They won't be at the bottom much at all.
When you reach the black stuff that looks like soil, put that in another pile. We'll divide this up later. Get everything out of the bin.
Step 4: Sort the Worms From the Compost
Take the pile of worms/compost, and divide it up into small piles, about two or three handfuls each. Since worms don't like light, they will begin to move towards the bottom of the pile. Start scooping compost off the top and putting it into a separate pile. You can move from one pile to the next, so that each time, the worms are able to move further down into the piles.
Eventually, you will have a pile that is mostly worms, and a pile that is mostly compost. You can put the worms back into your compost bin, and use the finished compost, mixed with dirt from the yard, for potting soil. Make sure that the compost has no recognizable food pieces in it. If it does, put it back in the bin.
Also don't worry if there are a few worms in the compost, since you've probably got dozens to spare in the bin already. If you like to fish, redworms (the kind used for vermicomposting; also called manure worms) work well as bait.
Step 5: Add Food Scraps, Paper Bedding, and Compost to Worm Bin
Now it's time to put everything that isn't finished compost back into the bin. We will work in layers, so that the worms are able to reach all the way to the bottom of the bin without borrowing through their own poop, which tends to collect in the bottom. Layers also help air and moisture move throughout the bin.
First, I put down a layer of compost from my outside compost pile into the bottom of the bin. This is made up of mostly intact grass clippings and mulched yard waste, since it hasn't been able to decompose as well during the cold winter weather. To jumpstart this compost pile, I added a handful of the worms that I isolated earlier. I'll continue to shuffle compost and worms back and forth from the pile to the bin, until everything is a nice uniform black soil.
The next layer is damp, shredded paper. Newspaper works well, but I just emptied out the paper shredder full of shredded credit card apps and other office waste. This provides "bedding" for the worms, allowing moisture and air to move through the bin. It also balances the carbon/nitrogen ratios in the bin.
After that, add the food scraps you set aside earlier, as well as anything else not eaten by the worms.
Alternate layers until you're out of material, or you've filled up the bin (but not all the way!).
Step 6: Let It Sit
You can add food scraps, more paper, or water to balance everything out, mostly you wait and let the worms do their thing. You can also stir up the bin with a garden tool, so that the bottom layers don't get compacted. In the spring, I'll add an instructable about planting a garden with compost.