Filters that have not been properly cleaned and primed, or if you have not fully cleaned and rinsed your tanks, the water from your initial filtrations may have a distinct, almost mineral taste. You can discard the first 2 or 3 filtrations.
If this issue continues, ensure that the black gaskets on the Black Berkey filters are correctly positioned on the upper tank and not with the wing nuts in the lower tank.
If required, you may need to clean your tanks again and reprime your filters.