The content_type helper function always adds a charset to the output.
It does this even with types that make no sense (e.g. image/png;charset=utf-8) and due to the implementation of the method, it's impossible to not send at least charset= if content_type is used, even if set :default_encoding, nil is used in addition to passing no charset along via the method params.
set :default_encoding, nil
Apart from this having to be fixed: Are there browsers that have issues with this?
Only set default charset for specific mime type. Closed by aa06ed5.