If the bedding is getting badly matted on the bottom, you can stir it up to break up the matted bedding and pull it up closer to the top. You don't need to do this often. Maybe once every two or three months. The worms won't like it, but in a day or two, they will forgive you and move forward with their lives.

The bedding should be about 6 inches deep. Any deeper, and the bedding tends to get matted up at the bottom. As the worms eat up the bedding, you can add more to bring the depth back up to 6 inches.

I should add a note here that if the bedding at the bottom of the bin is badly matted, you SHOULD stir the bedding to break it up, otherwise the worms will not eat the matted bedding at the bottom of the bin. If you harvest every 6 months, you will need to do this one time during that 6 month period, about half way through.

Stirred the bedding and all is well. Thanks sbryce.

When the bed gets a high concentration of earthworm castings, the bedding becomes compacted. If, after you turn it (or stir it), the bedding gets compacted again very soon then you need to change out the bedding because it has been consumed. When the bedding becomes too concentrated with castings, it's not healthy for the earthworms. Besides, you want to put it on your garden, right?

Here is a link that might be useful: Earthworm Castings

Once you've gotten started, the new bedding always goes on top and doesn't get as compacted. I only needed to stir/aerate my first bin to get at the compacted newspaper at the bottom. If I were to start a new tub bin now, I'd put a few inches of half composted VC in the bottom, then food, then worms and bedding. The only reason I don't is I switched to flow through style bins and don't start new bins much any more. (Even with my first FT, after putting newspaper down to keep everything in at the beginning, I put a few inches of composted VC in the bottom before anything else.)