This protocol describes how to extract inhibitor-free DNA from unsorted, homogenized bulk samples. of homogenate can be processed in one extraction, but there is also a miniaturized version for of input material, if less DNA is required. The protocol is based on the DNeasy PowerMax Soil Kit but costs much less. A lot of the buffers can be found in the following patent https://patents.google.com/patent/US7459548B2/en
Buchner et al. (Tue,) studied this question.