Responsa for Gittin 61:2

<big><strong>מתני׳</strong></big> המניח פירות להיות מפריש עליהן תרומה ומעשרות מעות להיות מפריש עליהן מעשר שני מפריש עליהן בחזקת שהן קיימין אם אבדו הרי זה חושש מעת לעת דברי ר' אלעזר

so the <i>terumah</i> of the tithe is set aside by estimate and by intention; and just as the owner has the right to set aside the 'great terumah', so he has the right to set aside the <i>terumah</i> of the tithe.<span class="x" onmousemove="('comment',' Even before giving it to the Levite. ');">⁴</span> <b><i>MISHNAH</i></b>. IF A MAN SETS ASIDE PRODUCE WITH THE IDEA OF RECKONING IT AS <i>TERUMAH</i> AND TITHE,<span class="x" onmousemove="('comment',' Lit., 'of setting aside on their account', i.e., with the idea of making it terumah or tithe for other produce. ');">⁵</span> OR MONEY WITH THE IDEA OF RECKONING IT AS SECOND TITHE,<span class="x" onmousemove="('comment',' The tithe which had to be turned into money to be spent in Jerusalem. V. Deut. XIV, 22-27. ');">⁶</span>

Teshuvot Maharam