According to Brad Smith, at BeerSmith, a crock was found near Kulmbach Germany dating back to 800 BC with blackened barley bread inside – the standard material used to brew ancient Germanic beer. He says, "The key to making a good Schwarzbier is achieving the appropriate balance between the malt base, specialty grains and hops so that none of these ingredients overpowers the others."
"...The key is achieving the dark color needed without providing too much roasted flavor."
None of the following are attempts to reproduce the wonderful Black Radish, but its a start.
Pitch Black Schwarzbier - All Grain
Pitch Black Schwarzbier - Extract
Schwarzbieresque - Extract
Storm King Schwarzbier - All Grain
Schwarzbier’s are on my brew list but haven’t yet. Sounds intriguing though so I may need to do one sooner rather than later.
Not sure how long you’ve been brewing so forgive the presumption here. If you do a lager, make very sure you include a diaceytl rest during fermentation otherwise you lager will taste like movie popcorn butter. I would also recommend a very healthy yeast starter and get the wort chilled down to about your fermentation temp (50 degrees?) before you pitch.