vermicompost windrows question
Here's some background and my question is at the bottom. I help to manage a 3,000 sqft vermicompost facility (VCF) in Kerala, India and I'm new to the world of vermicompost. We use simple windrows about 20 inches high and 36 inches wide. At another nearby location we have a thermophilic compost operation (TCO). They have a rotating screen filter to filter the compost piles (which are actually mulch piles with very little finished compost inside). The TCO piles are made from food waste and lots of carbon materials like wood chips, shredded leaves and sticks.
The smallest filter mesh size is about 5mm. The fine mulch that falls out of this is used to make the VC windrows. We let the worms (esenia fetida) work on the windrows for about 3 months or so. When we collect the worm castings the bottom 3 or 4cm of the VC piles is uneaten by the worms. We take that uneaten bottom material (UBM) and put it on top of other VC piles and the worms finish it off. In addition to daily watering, about every 3 or 4 days we pour cow dung slurry on all the VC piles and then stop feeding and watering about 12 days before collecting.
A friend of mine who has studied worm composting says that the UBM can be considered finished vermicompost. That surprised me. When I look at the UBM its just small pieces of undigested wood (sawdust size up to 5mm). My understanding is that undigested wood cannot be considered compost since it would attract bacteria and be a nutrient "sink" in the soil.
Now I want to get some expert opinions. Can the UBM be considered as finished vermicompost? Low quality vermicompost? Or not vermicompost at all but just a rich fine mulch?
Let me know if you need any other details. Thanks! Kind Regards,