Here is the bottom line: Without high-quality, high-diversity compost, you cannot brew high-quality, highly-diverse (biologically) tea.  That's it.  The compost you use in your tea is the most important factor.  There are several books on composting.  One of the best is: Field Guide to On-Farm Composting.  It is published by Natural Resource, Agriculture, and Engineering Service (NRAES). It is publication number NRAES-114.  www.nraes.org

So what is the big deal about composting?  You need to manage several things to produce really good compost instead of a pile of garbage.  These are:

Carbon-To-Nitrogen ration (C:N)                20:1 through 40:1
Moisture Content                                            40-65%
Oxygen                                                            Greater than 5%
Particle Size                                                    .5 to 2"
Porosity of Pile                                              Greater than 40%
Bulk Density (lbs./cu yd)                              800-1200
pH                                                                    5.5 to 9.0
Temperature                                                    110 to 150 during active composting. 

Table taken from NRAES-114, PAGE 8.