\addbibresource doesn't work with file contents

Question

I want to cite using the \filecontents command for the books.

But it doesn't recognize the books. It only shows the keyword in bold. It says citation "elch" is undefined

    \documentclass[12pt]{article}

    \usepackage[ngerman]{babel}
    \usepackage[a4paper, text={16.5cm, 25.2cm}, centering]{geometry}
    \usepackage[sfdefault]{ClearSans}
    \usepackage[utf8]{inputenc}
    \setlength{\parskip}{1.2ex}
    \setlength{\parindent}{0em}

    \usepackage{filecontents}


    \begin{filecontents}{ref.bib}
    @BOOK{elch,
    AUTHOR = "Karall, Benedikt and Schwarz, Markus",
    TITLE = "{Eine Studie zur Elchplicht}",
    PUBLISHER = "JG-Verlag",
    YEAR = 2012}
    \end{filecontents}


    \usepackage[style=authoryear, backend=biber]{biblatex}
    \addbibresource{ref.bib}

    \begin{document}

    Die exakte Herleitung kann in \parencite{elch} nachgelesen werden.

   \end{document}