After you get a good accumulation of castings, you will want to remove them without losing your worms. Worms will not hurt your garden (in fact, they may even help a bit) but the goal is to keep the worms in the bin so they can keep doing what they do best – breaking down your food!
Stacking bins exist to make the harvest of vermicompost as easy as possible. Once you have had a second tray filled with food and bedding for a couple of weeks, most of your worms will have migrated upward to the new tray, leaving your original tray devoid of worms but full of castings. Remove the castings and your tray is ready to be filled with new food waste and put on top of the stack.
The “pyramid method” is your best bet if you are using a single layer worm bin. Find the areas that you fed longest ago and are the most broken down and remove them, placing them on a tarp or other surface in small pyramid shapes. It is best to do this on a sunny day in a bright spot. The worms are light-averse and will dive below the surface to escape the sunlight. Wait 5 minutes and remove the top layer of castings. Repeat this process until all of the worms are together at the bottom of your pile and then return the worms to your bin.