Line spacing in title of Beamer poster

Question

I am trying to make the line spacing bigger in the title of a Beamer poster but the second argument of fontsize is not working. This question seems to be the same as mine (although not for Beamer poster), but the solution provided there is not working in my case, I don't know why.

\documentclass[final,t]{beamer}
\usepackage[orientation=portrait]{beamerposter}
\setbeamercolor{headline}{fg=white,bg=gray}
\setbeamercolor{title in headline}{fg=white}
\setbeamertemplate{headline}{

    \leavevmode
    \begin{beamercolorbox}[wd=\paperwidth]{headline}
        \begin{columns}[T]
            \begin{column}{.5\paperwidth}
                \vskip4ex
                \begin{center}
                    \vskip 2.75ex
                    % Changing the 2nd argument of fontsize does not change anything
                    \usebeamercolor{title in headline}{\color{fg}\textbf{\fontsize{60}{10} \selectfont \inserttitle}}
                    \vskip 2.75ex
                \end{center}
                \vskip4ex
            \end{column}
        \end{columns}
    \end{beamercolorbox}
}
\title{A long title of a paper whose interline spacing I want to increase}
\begin{document}
\begin{frame}{} 
\end{frame}
\end{document}

Answer 1

You want

1. to end the current paragraph before switching back to a smaller font
2. the second argument with the baseline skip should normally be bigger than the font size

I'd also avoid adding spaces manually and adjust the sep of the beamercolorbox instead:

\documentclass[final,t]{beamer}
\usepackage[orientation=portrait]{beamerposter}
\setbeamercolor{headline}{fg=white,bg=gray}
\setbeamerfont{title}{series=\bfseries,size*={60}{72}}
\setbeamertemplate{headline}{%
    \leavevmode
    \begin{beamercolorbox}[wd=\paperwidth,sep=8ex,center]{headline}
        \begin{minipage}{.5\paperwidth}
                \centering
                \usebeamerfont{title}%
                \inserttitle\par
        \end{minipage}
    \end{beamercolorbox}
}
\title{A long title of a paper whose interline spacing I want to increase}
\begin{document}
\begin{frame} 
\end{frame}
\end{document}