\input{./vars}

\begin{document}
\begin{tabular}{|l|l|l|l|}
\hline
\textbf{\begin{tabular}[c]{@{}l@{}}Temperature\\ in °C\end{tabular}} & \textbf{\begin{tabular}[c]{@{}l@{}}Temperature\\ in °F\end{tabular}} & \textbf{\begin{tabular}[c]{@{}l@{}}Starter\\ recently fed?\end{tabular}} & \textbf{\begin{tabular}[c]{@{}l@{}}Amount\\ of starter in\%\end{tabular}} \\ \hline
30                                                                   & 86                                                                   & Yes                                                                      & 5                                                                         \\ \hline
25                                                                   & 77                                                                   & Yes                                                                      & 10                                                                        \\ \hline
20                                                                   & 68                                                                   & Yes                                                                      & 15                                                                        \\ \hline
30                                                                   & 86                                                                   & No                                                                       & 2.5                                                                       \\ \hline
25                                                                   & 77                                                                   & No                                                                       & 5                                                                         \\ \hline
20                                                                   & 68                                                                   & No                                                                       & 10                                                                        \\ \hline
\end{tabular}
\end{document}