Halacha

הלכה א
אַחַר שֶׁמַּפְרִישִׁין תְּרוּמָה גְּדוֹלָה מַפְרִישׁ אֶחָד מֵעֲשָׂרָה מִן הַנִּשְׁאָר וְזֶהוּ הַנִּקְרָא מַעֲשֵׂר רִאשׁוֹן וּבוֹ נֶאֱמַר (במדבר יח כד) "כִּי אֶת מַעְשַׂר בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָרִימוּ לַה'" וְגוֹ'. וְהַמַּעֲשֵׂר הַזֶּה לִלְוִיִּים זְכָרִים וּנְקֵבוֹת שֶׁנֶּאֱמַר (במדבר יח כא) "וְלִבְנֵי לֵוִי הִנֵּה נָתַתִּי כָּל מַעֲשֵׂר בְּיִשְׂרָאֵל לְנַחֲלָה":
כסף משנה
1.
After separating the great terumah,1This is the preferable course of behavior. If, however, one separates the tithes before terumah, the separation is binding. one should separate one tenth of the remaining produce2Thus it is not a tenth of the entire crop. and this is called the first tithe. Concerning it [Numbers 18:24] states: "For the tithes of the children of Israel that they will separate to God."3Sefer HaMitzvot (positive commandment 127) and Sefer HaChinuch (mitzvah 395) include this commandment among the 613 mitzvot of the Torah.
These tithes are given to Levites, males and females, as [ibid.] states: "And I gave the Levites all of the tithes of the children of Israel as an inheritance."

הלכה ב
מַעֲשֵׂר רִאשׁוֹן מֻתָּר בַּאֲכִילָה לְיִשְׂרָאֵל וּמֻתָּר לְאָכְלוֹ בְּטֻמְאָה שֶׁאֵין בּוֹ קְדֻשָּׁה כְּלָל. וְכָל מָקוֹם שֶׁנֶּאֱמַר בְּמַעַשְׂרוֹת קֹדֶשׁ אוֹ פְּדִיָּה אֵינוֹ אֶלָּא מַעֲשֵׂר שֵׁנִי. וּמִנַּיִן שֶׁמַּעֲשֵׂר רִאשׁוֹן חֻלִּין שֶׁנֶּאֱמַר (במדבר יח כז) "וְנֶחְשַׁב לָכֶם תְּרוּמַתְכֶם כַּדָּגָן מִן הַגֹּרֶן וְכַמְלֵאָה מִן הַיָּקֶב" מָה גֹּרֶן וְיֶקֶב חֻלִּין לְכָל דָּבָר אַף מַעֲשֵׂר רִאשׁוֹן שֶׁנִּטְּלָה תְּרוּמָתוֹ חֻלִּין לְכָל דָּבָר. לְפִיכָךְ בַּת לֵוִי שֶׁנִּשְׁבֵּית אוֹ שֶׁנִּבְעֲלָה בְּעִילַת זְנוּת נוֹתְנִין לָהּ הַמַּעֲשֵׂר וְאוֹכֶלֶת. אֲבָל מִי שֶׁשָּׁמְעָה שֶׁמֵּת בַּעְלָהּ אוֹ הֵעִיד לָהּ עֵד אֶחָד וְנִסֵּת וְאַחַר כָּךְ בָּא בַּעְלָהּ קָנְסוּ אוֹתָהּ חֲכָמִים שֶׁתִּהְיֶה אֲסוּרָה בְּמַעֲשֵׂר:
כסף משנה
2.
An Israelite is permitted to partake of the first tithe, and it may be eaten in a state of ritual impurity, because it is not holy.4I.e., unlike terumah where these restrictions apply. Whenever the term "holy" or "redemption" is used with regard to the tithes, the intent is the second tithe.5Which must be eaten in Jerusalem in a state of ritual purity.
What is the source from which we learn that the first tithe is ordinary produce? [Ibid.:27] states: "And your terumah will be considered for you as grain from your grainheap and the fullness of the vat." Just as a grainheap and a vat [contain] ordinary produce, so, too, once terumat ma'aser has been separated from the first tithe,6Until terumat ma'aser has been separated from it, however, we may not partake of it (Radbaz). it is ordinary produce in all regards. For this reason, when the daughter of a Levite has been taken captive7And we fear that she was raped by her captors. With regard to terumah, by contrast, once the daughter of a priest engages in forbidden relations, she is forbidden to partake of it (Hilchot Terumah 6:7). Our Sages did not decree that a Levite's daughter who engages in forbidden relationships should not be allowed to partake of terumah, for it is uncommon for a woman to engage in forbidden relationships (Yevamot 91a). or she engaged in forbidden relations, she can be given tithes and she may partake of it. When, however, there was a report that a woman's husband died or one witness testified that he died, she married8If, however, she did not marry, she is not forbidden, even if she was consecrated by another man. and then her husband appeared, our Sages penalized her and ruled that she is forbidden to partake of the tithes.9I.e., this is a Rabbinic decree, enacted to maintain the moral level of the Jewish people.

הלכה ג
לְוִיִּים וְכֹהֲנִים מַפְרִישִׁין מַעֲשֵׂר רִאשׁוֹן כְּדֵי לְהַפְרִישׁ מִמֶּנּוּ תְּרוּמַת מַעֲשֵׂר. וְכֵן הַכֹּהֲנִים מַפְרִישִׁין שְׁאָר תְּרוּמוֹת וּמַעַשְׂרוֹת לְעַצְמָן. וּלְפִי שֶׁהַכֹּהֲנִים נוֹטְלִין מִן הַכּל יָכוֹל יֹאכְלוּ פֵּרוֹתֵיהֶן בְּטִבְלָן תַּלְמוּד לוֹמַר (במדבר יח כח) "כֵּן תָּרִימוּ גַּם אַתֶּם" מִפִּי הַשְּׁמוּעָה לָמְדוּ אַתֶּם אֵלּוּ הַלְוִיִּם גַּם אַתֶּם לְרַבּוֹת אֶת הַכֹּהֲנִים:
כסף משנה
3.
The Levites and the priests should separate the first tithe so that they can separate terumat ma'aser from it.10I.e., since the priests and the Levites are allowed to keep the tithes, one might ask: Why is it necessary for them to separate it at the outset? The Rambam answers that the separation is necessary, because until terumat ma'aser is separated from the tithes, it is forbidden to partake of them. Similarly, the priests must separate other types of terumah11With the expression "other types of terumah," the Rambam includes challah and bikkurim. See Hilchot Terumah 15:20. and tithes12The intent is only the first tithe. The second tithe and the tithe for the poor are not given to the priests. for themselves.13They may not, however, partake of the produce without making these separations as the Rambam proceeds to explain. Since the priests receive all types of agricultural gifts, is it possible for them to partake of the produce without these separations having been made? [Numbers 18:28] states: "And so shall you separate, also you...." "You" includes the Levites. "Also you" includes the priests.

הלכה ד
אֵין מוֹצִיאִין הַמַּעֲשֵׂר מִיַּד הַכֹּהֲנִים שֶׁנֶּאֱמַר (במדבר יח כו) "כִּי תִקְחוּ מֵאֵת בְּנֵי יִשְׂרָאֵל" וְכֵן כָּל מַתְּנוֹת כְּהֻנָּה אֵין מוֹצִיאִין אוֹתָן מִכֹּהֵן לְכֹהֵן. וְעֶזְרָא קָנַס אֶת הַלְוִיִּם בִּזְמַנּוֹ שֶׁלֹּא יִתְּנוּ לָהֶן מַעֲשֵׂר רִאשׁוֹן אֶלָּא יִנָּתֵן לַכֹּהֲנִים לְפִי שֶׁלֹּא עָלוּ עִמּוֹ לִירוּשָׁלַיִם:
כסף משנה
4.
We do not expropriate the tithes from the priests, as [ibid.:26] states: "When you take from the children of Israel...."14I.e., from an Israelite and not from a priest. Similarly, none of the presents given to the priests must be given from one priest to another priest.15A priest must separate the presents. He need not, however, give them to another priest, but instead may keep them for himself.
Ezra penalized the Levites in his time16There are some who interpret the Rambam as implying that the penalty was applied only in Ezra's era, but not in subsequent generations. Indeed, we find that even Sages gave their tithes to Levites (Ma'aser Sheni 5:9). For this reason, it appears that Ezra's penalty was that if there was both a priest and a Levite present, the tithes should be given to a priest, but they could also be given to a Levite (Radbaz). Alternatively, in Ezra's generation, the tithes should be given only to the priests. Subsequently, however, when more Levites ascended and settled in Eretz Yisrael, the decree was rescinded and tithes could also be given to the Levites. Nevertheless, in order not to nullify Ezra's words entirely, it was still possible to give the tithes to the priests (Kessef Mishneh). [Note, however, the Rambam's Commentary to the Mishnah (Ma'aser Sheni 5:15) which indicates that the tithes were given to the priests in the generations after Ezra as well. See also Hilchot Ma'aser Sheni 11:14.] All agree that the Levites themselves were never required to give the tithes to the priests.
The Minchat Chinuch (Mitzvah 395) asks: How was it possible for Ezra to nullify the Torah's command? For the Scriptural obligation is to give the tithes to the priests. He answers that in Ezra's time, the mitzvah to tithe was only Rabbinic in origin (see Hilchot Terumot, ch. 1). Hence, it was possible for him to make the priests the recipients.
because they did not ascend to Jerusalem with him17See Ezra 8:15 which states that the descendants of the Levites were not found among the people who returned to Israel from Babylon. There were many among the Jewish people who had achieved financial security and comfortable living circumstances in Babylon and did not want to give this up to live in the Holy Land. Nevertheless, aside from the Levites, there was no distinct group that did not return to Israel in significant numbers. and ordained that the first tithe should be given solely to the priests.

הלכה ה
הָאוֹכֵל פֵּרוֹתָיו טְבָלִין וְכֵן לֵוִי שֶׁאָכַל הַמַּעֲשֵׂר בְּטִבְלוֹ אַף עַל פִּי שֶׁהֵן חַיָּבִין מִיתָה לַשָּׁמַיִם אֵין מְשַׁלְּמִין הַמַּתָּנוֹת לְבַעֲלֵיהֶן שֶׁנֶּאֱמַר (במדבר יח כד) "אֲשֶׁר יָרִימוּ לַה'" אֵין לְךָ בָּהֶן כְּלוּם עַד שֶׁיָּרִימוּ אוֹתָן. וּבְחוּצָה לָאָרֶץ מֻתָּר לְאָדָם לִהְיוֹת אוֹכֵל וְהוֹלֵךְ תְּחִלָּה וְאַחַר כָּךְ מַפְרִישׁ תְּרוּמָה וּמַעַשְׂרוֹת:
כסף משנה
5.
When a person partakes of his produce while it is tevel18I.e., before terumah and the tithes have been separated. or a Levite partakes of the tithes while they are tevel,19I.e., before terumat ma'aser has been separated. although they are liable for death at the hand of Heaven,20Se Hilchot Ma'achalot Assurot 10:19. they are not liable to make reimbursement to the owners.21I.e., the priests (or the Levites) who would be given the terumah or the tithes. With regard to terumah, by contrast, when a person partakes of terumah unknowingly, he is required to make restitution. See Hilchot Terumah 6:6. [This is derived from ibid.:24:] "...that they will separate to God." [Implied is that the recipients] do not have any share in them until they have been separated.
In the Diaspora,22In the lands directly bordering on Eretz Yisrael where our Sages ordained that the agricultural laws be observed. See Hilchot Terumah 1:6. it is permitted for a person to continue eating and afterwards, separate terumah and the tithes.23Since the obligation to make these separations from the crops is Rabbinic in origin, our Sages granted this leniency. See Hilchot Terumah 1:21.

הלכה ו
מְעַשְּׂרִין מִמָּקוֹם זֶה עַל מָקוֹם אַחֵר וְאֵינוֹ צָרִיךְ לְעַשֵּׂר מִן הַמֻּקָּף. אֲבָל אֵין מְעַשְּׂרִין מִמִּין עַל שֶׁאֵינוֹ מִינוֹ וְלֹא מִן הַחַיָּב עַל הַפָּטוּר וְלֹא מִן הַפָּטוּר עַל הַחַיָּב וְאִם עִשֵּׂר אֵינוֹ מְעֻשָּׂר:
כסף משנה
6.
We can separate tithes from produce in one place for produce in another place. They need not be grouped together.24In contrast to terumah, in which instance, the initial preference is to separate the terumah from the same produce for which it is being taken (Hilchot Terumah 3:17). We do not, however, separate tithes from one species for another species,25This holds true for terumah as well, as stated in Hilchot Terumah 5:3. nor from produce for which we are obligated to separate tithes for produce from which we are exempt from separating, nor from produce for which we are exempt from separating tithes for produce from which such a separation is required.26This also applies with regard to terumah, see ibid.:2, 12. If one made a separation in any of the above instances, [the produce separated] is not considered as tithes.27It need not be given to a Levite and if necessary, new tithes must be separated.

הלכה ז
כָּל שֶׁאָמַרְנוּ בִּתְרוּמָה אֵין תּוֹרְמִין מִזֶּה עַל זֶה כָּךְ בְּמַעֲשֵׂר אֵין מְעַשְּׂרִין מִזֶּה עַל זֶה. וְכָל שֶׁאָמַרְנוּ בִּתְרוּמָה אִם תָּרַם תְּרוּמָתוֹ תְּרוּמָה כָּךְ בְּמַעֲשֵׂר אִם הִפְרִישׁ מַעַשְׂרוֹתָיו מַעַשְׂרוֹת. וְכָל שֶׁהוּא פָּטוּר מִן הַתְּרוּמָה פָּטוּר מִן הַמַּעֲשֵׂר. וְכָל הַתּוֹרֵם מְעַשֵּׂר. כָּל שֶׁאָמַרְנוּ בָּהֶן לֹא יִתְרֹמוּ וְאִם תָּרְמוּ תְּרוּמָתָן תְּרוּמָה כָּךְ אִם עִשְּׂרוּ מַעַשְׂרוֹתֵיהֶן מַעַשְׂרוֹת. וְכָל שֶׁאֵין תְּרוּמָתוֹ תְּרוּמָה כָּךְ אֵין מַעַשְׂרוֹתֵיהֶן מַעַשְׂרוֹת:
כסף משנה
7.
Whenever we said with regard to terumah, that terumah may not be separated from one type of produce for another,28E.g., produce that has been reaped for produce that is attached to the ground (ibid.:9), produce reaped in one year for produce reaped in another year (ibid.:11), or produce from the Diaspora for produce from Eretz Yisrael (ibid.:12). tithes may not be separated from one such type of produce for another such type. And whenever we said that the separation of terumah from [one type of produce] is acceptable [after the fact],29I.e., instances where a separation of terumah is undesirable, nevertheless, after the fact, it is acceptable. For example, one separated produce for which all the work concerning it was not completed (ibid.:4); one separates lower grade produce as terumah for higher grade produce (ibid.:8); or one unknowingly separated impure produce as terumah for pure produce. if one separated tithes from such produce, it is acceptable. Whenever produce is exempt from the obligation to have terumah separated,30For example, produce not fit for human consumption (ibid. 2:1); produce that was leket, pe'ah, or the like (ibid.:9). it is also exempt from the obligation to have tithes separated. All those individuals who may separate terumah may separate the tithes. And all those concerning whom it was said that they should not separate terumah, but if they did separate it, the separation is effective,31A person who is deaf, but not mute, a mute who can hear, but not speak, a person who is naked, a person who is drunk and a blind person (ibid. 4:4). so too, if they separate the tithes, the separation is effective. And whenever a person's separation of terumah is not effective,32A deaf-mute, a mentally or emotionally unstable person, a minor, a gentile who separated terumah from produce belonging to a Jew, even with his permission, and a person who separate terumah from produce that does not belong to him without the owner's permission (ibid.:2). his separation of tithes is also not effective.

הלכה ח
הָאוֹמֵר לַחֲבֵרוֹ הֲרֵינִי מְעַשֵּׂר עַל יָדֶיךָ אֵינוֹ צָרִיךְ לַעֲמֹד עִמּוֹ עַד שֶׁיִּרְאֶה אִם יְעַשֵּׂר אוֹ לֹא יְעַשֵּׂר. וְאִם אָמַר הוּא לַחֲבֵרוֹ עַשֵּׂר עַל יָדִי צָרִיךְ לַעֲמֹד עִמּוֹ:
כסף משנה
8.
When a person tells a colleague: "I will tithe through your agency," he does not have to stand with him to see whether he tithed or did not tithe.33Since he willingly appointed him as an agent, we assume that he relies on him and can follow the accepted presumption that an agent will carry out the task assigned to him. [Our translation and commentary follow the gloss of the Radbaz. Others offer different interpretations.] If [the agent] tells a colleague: "Tithe using me as an agent," he must stand with him.34Since he did not appoint him voluntarily, we are not certain that he will carry out the agency in good faith.

הלכה ט
הֶחָרוּבִין אֵינָן חַיָּבִין בְּמַעַשְׂרוֹת אֶלָּא מִדִּבְרֵיהֶם. לְפִי שֶׁאֵינָן מַאֲכָל [רֹב] אָדָם. וְהַשְּׁקֵדִים הַמָּרִים בֵּין בְּגָדְלָן בֵּין בִּקְטַנָּן פְּטוּרִין לְפִי שֶׁאֵינָן אֹכֶל:
כסף משנה
9.
The obligation to tithe carobs is only Rabbinic in origin,35The Ra'avad differs with the Rambam and maintains that according to Scriptural Law, the only trees from which we are required to separate the tithes are grapes and olives. As explained in the notes to Hilchot Terumah 2:1, this is a difference of opinion involving many authorities. for they are not eaten by most people.36Based on Hilchot Ma'aser Sheni 1:3, it appears that here the Rambam is speaking of carobs that grow in Tzalmona or other species that are usually not eaten. The carobs that grow commonly and are eaten by many must be tithes according to Scriptural Law.
Those that grow in Tzalmona and the like are also eaten by some people. Hence the Rabbis ordained that they be tithed. Species of produce that are not usually consumed by people are exempt, as stated in the following clause.
Bitter almonds, whether large or small,37When such almonds are small, they are not bitter. Nevertheless, they are still unfit to be eaten because they have not fully matured (see Rashi, Chullin 25b). are exempt, for they are not considered food.38Even though some may partake of them, the majority do not. Indeed, the minority is so insignificant that we do not require a separation of terumah even according to Rabbinic Law.

הלכה י
אִילָן שֶׁנְּטָעוֹ בְּתוֹךְ הַבַּיִת פָּטוּר מִמַּעַשְׂרוֹת שֶׁנֶּאֱמַר (דברים יד כב) "עַשֵּׂר תְּעַשֵּׂר אֵת כָּל תְּבוּאַת זַרְעֶךָ הַיֹּצֵא הַשָּׂדֶה". וְיֵרָאֶה לִי שֶׁהוּא חַיָּב בְּמַעַשְׂרוֹת מִדִּבְרֵיהֶם שֶׁהֲרֵי תְּאֵנָה הָעוֹמֶדֶת בֶּחָצֵר חַיָּב לְעַשֵּׂר פֵּרוֹתֶיהָ אִם אֲסָפָן כְּאַחַת:
כסף משנה
10.
A tree that is planted inside a house is exempt from the obligations of the tithes, as [indicated by Deuteronomy 14:22]: "You shall certainly tithe all the produce of your crops that grow in the field."39It is produce of the field from which we must tithe (the Jerusalem Talmud, Orlah 1:2). It appears to me that tithes must be separated from this produce according to Rabbinic Law, for one is required to tithe the fruit of a fig tree that stands in a courtyard if it was harvested at one time.40If, however, the fruit is picked one by one, a person is not obligated to tithe it.
This law is stated in the Mishnah (Ma'aserot 3:8). Now a courtyard is not considered a field. Hence in order that this law not contradict the law cited from the Jerusalem Talmud, we must assume that the Mishnah is speaking according to Rabbinic Law, while the Jerusalem Talmud is speaking according to Scriptural Law. The Ra'avad differs with this ruling and differentiates between produce growing in a courtyard and that which grows in a house. The Radbaz and the Kessef Mishneh support the Rambam's ruling.

הלכה יא
בְּצָלִים שֶׁהִשְׁרִישׁוּ זֶה בְּצַד זֶה אֲפִלּוּ הִשְׁרִישׁוּ בְּקַרְקַע עֲלִיָּה פְּטוּרִין מִן הַמַּעַשְׂרוֹת. נָפְלָה עֲלֵיהֶן מַפּלֶת וַהֲרֵי הֵן מְגֻלִּין הֲרֵי אֵלּוּ כִּנְטוּעִין בַּשָּׂדֶה וְחַיָּבִין בְּמַעַשְׂרוֹת:
כסף משנה
11.
When onions [stored in a home] grew roots next to each other, even if they grew roots in the earth of a loft, they are exempt from tithes.41I.e., they are exempt according to Scriptural Law, and even according to Rabbinic Law, there is no obligation to separate tithes, because the person would not desire to have the plants grow (Or Sameach). If a landslide covered them,42Destroying the roof of the loft. and they are thus open [to the skies], it is as if they have been planted in the field and one is obligated to tithe them.

הלכה יב
הַמְשַׁמֵּר שָׂדֵהוּ מִפְּנֵי עֲנָבָיו וּבָא אַחֵר וְאָסַף אֶת הַתְּאֵנִים הַנִּשְׁאָרוֹת בְּאוֹתָהּ שָׂדֶה. אוֹ שֶׁהָיָה מְשַׁמֵּר שָׂדֵהוּ מִפְּנֵי הַמִּקְשָׁאוֹת וְהַמִדְּלָעוֹת וּבָא אֶחָד וְאָסַף אֶת הָעֲנָבִים הַנִּשְׁאָרִים שָׁם הַמְפֻזָּרִים בַּשָּׂדֶה. בִּזְמַן שֶׁבַּעַל הַשָּׂדֶה מַקְפִּיד עֲלֵיהֶן אֲסוּרִין מִשּׁוּם גֵּזֶל וּלְפִיכָךְ חַיָּבִין בְּמַעֲשֵׂר וּבִתְרוּמָה. אֵין בַּעַל הַשָּׂדֶה מַקְפִּיד עֲלֵיהֶן מֻתָּרִין מִשּׁוּם גֵּזֶל וּפְטוּרִין מִן הַמַּעֲשֵׂר:
כסף משנה
12.
[The following laws apply when someone is] protecting his field because of grapes43The Rambam is speaking about an instance where the figs and the other fruits growing in the field have for the most part been harvested. There were, however, a few figs left growing in scattered places around the field. The grapes, however, grow later than the other crops and hence, had not been harvested yet. The owner was protecting his field for the sake of his grapes. The question is: Are the other fruits considered as ownerless because the owner is no longer primarily concerned with them? Or do we say that since he is guarding his field because of the grapes, he is also guarding the other produce? and another person comes and collects the figs that remain in that field or he was guarding his field because of the zucchini and squash44Which grow even later than grapes. and another person came and gathered the grapes which were scattered in the field. When [it is known] that the owner of the field is concerned with the leftover produce, it is forbidden to take it; [doing so] is stealing.45Even though it has little value. We are forbidden to take even the slightest amount of a colleague's property against his will. Hence, tithes and terumah must be separated from the crops. If the owner of the field is not concerned with it, it is permitted [to take it;46It is as if he has declared them ownerless (Radbaz). See a parallel ruling in Hilchot Ishut 5:8. it is not] theft. Hence, they are exempt from the tithes.47For ownerless produce need not be tithed. Similarly, terumah need not be separated from it (Radbaz, based on Hilchot Terumah 2:11).

הלכה יג
אֵין מְעַשְּׂרִין אֶלָּא מִן הַמֻּבְחָר שֶׁנֶּאֱמַר (במדבר יח ל) "בַּהֲרִימְכֶם אֶת חֶלְבּוֹ מִמֶּנּוּ וְנֶחְשַׁב לָכֶם כִּתְבוּאַת גֹּרֶן וְכִתְבוּאַת יָקֶב". כְּשֵׁם שֶׁמַּעֲשֵׂר שֶׁמַּפְרִישִׁים הַלְוִיִּם מִן הַחֵלֶב שֶׁבּוֹ כָּךְ מַעֲשֵׂר שֶׁמַּפְרִישִׁים יִשְׂרָאֵל מִן הַגֹּרֶן וּמִן הַיֶּקֶב מִן הַחֵלֶב שֶׁבּוֹ:
כסף משנה
13.
Only the most choice produce should be separated as tithes,48The same concept applies with regard to terumah, as stated in Hilchot Terumah 2:4,6. as [Numbers 18:30] states: "When you separate the choice portion from it, and it will be considered for the Levites49This is both the correct wording of the verse and the manuscript copies of the Mishneh Torah. The standard printed text is in error. as the produce of the grainheap and the produce of the vat." Just as the Levites must separate the choicest portions of the tithes, the Israelites who separate from the grainheap and the vat separate the choicest portions.

הלכה יד
אֵין מְעַשְּׂרִין בְּאֹמֶד אֶלָּא בְּמִדָּה אוֹ בְּמִשְׁקָל אוֹ בְּמִנְיָן. וְכָל הַמְדַקְדֵּק בַּשִּׁעוּר מְשֻׁבָּח. וְהַמַּרְבֶּה בְּמַעַשְׂרוֹת מַעַשְׂרוֹתָיו מְקֻלְקָלִין שֶׁהֲרֵי הַטֶּבֶל מְעֹרָב בָּהֶן. וּפֵרוֹתָיו מְתֻקָּנִין:
כסף משנה
14.
We may not separate tithes by estimation.50See Avot 1:16. In contrast terumah should be separated in this manner (Hilchot Terumah 3:4). Instead, one must do so through measuring,51The volume of the produce. weight, or number.52The order of preference is number, volume, weight. See Terumot 4:6. One who is precise in the measurement is praiseworthy. When one gives an extra amount as the tithes, his tithes are flawed, because untithed produce is mixed with them.53For the extra amount of produce is not tithes, because the tithes represent an exact sum. Nor is it considered ordinary produce from which tithes were separated, because it was placed with the tithes. Instead, it is considered as ordinary produce from which tithes were not separated. [The remainder of] his produce has, however, been made fit for use.

הלכה טו
הַמַּפְרִישׁ מִקְצָת מַעֲשֵׂר אֵינוֹ מְעַשֵּׂר אֶלָּא כְּמִי שֶׁחָלַק אֶת הָעֲרֵמָה. אֲבָל צָרִיךְ [לְהַפְרִישׁ] מִזֶּה הַחֵלֶק שֶׁיּוֹצִיא מַעֲשֵׂר שֶׁלּוֹ. כֵּיצַד. הָיוּ לוֹ מֵאָה סְאָה הִפְרִישׁ מֵהֶם חֲמִשָּׁה לְשֵׁם מַעֲשֵׂר אֵינוֹ מַעֲשֵׂר וְאֵינוֹ יָכוֹל לְהַפְרִישׁ עַל הֶחָמֵשׁ סְאִין מַעֲשֵׂר בְּמָקוֹם אַחֵר אֶלָּא מַפְרִישׁ מֵהֶן חֲצִי סְאָה שֶׁהִיא הַמַּעֲשֵׂר שֶׁלָּהֶן:
כסף משנה
15.
When a person separates a portion of the tithes, they are not considered as tithes. Instead, it is as if someone divided the grainheap. He must, however, separate from the portion set aside the tithes that are appropriate for it.
What is implied? A person had 100 se'ah. He set aside five se'ah as the tithes. [These five se'ah] are not considered as tithes.54For giving them does not fulfill the requirement. He cannot separate tithes for [these five se'ah] from another source.55Although usually, one may set aside tithes from one collection of produce for another (Halachah 6), an exception is made in this instance, because he originally separated this produce with the intent that it be tithes [the Rambam's Commentary to the Mishnah (Terumot 4:1)]. it would appear that one is separating tithes from produce for which one is required to separate tithes for produce for which one is not obligated to make such a separation (see notes to Halachah 7). The Ra'avad differs with the Rambam concerning this ruling, advancing a different interpretation of Terumot 4:1. Instead, he should separate half a se'ah from them. It is their tithes.

הלכה טז
הַמַּפְרִישׁ מַעֲשֵׂר זֶה מְבָרֵךְ תְּחִלָּה כְּדֶרֶךְ שֶׁמְּבָרְכִין עַל הַמִּצְוֹת. וְכֵן מְבָרֵךְ עַל מַעֲשֵׂר שֵׁנִי וְעַל מַעֲשַׂר עָנִי וְעַל מַעֲשֵׂר מִן הַמַּעֲשֵׂר מְבָרֵךְ עַל כָּל אֶחָד בִּפְנֵי עַצְמוֹ. וְאִם הִפְרִישׁ הַכּל זֶה אַחַר זֶה מִיָּד וְלֹא סָח בֵּינֵיהֶן כּוֹלְלָן בִּבְרָכָה אַחַת וּמְבָרֵךְ לְהַפְרִישׁ תְּרוּמוֹת וּמַעַשְׂרוֹת:
כסף משנה
16.
When a person separates the [first] tithe, he should recite a blessing first, as one recites a blessing [before observing] any of the mitzvot.56See Hilchot Berachot 11:6, 12; Hilchot Terumah 2:16. Similarly, he should recite a blessing [before separating] the second tithe, the tithe given to the poor, and the tithe of a tithe.57I.e., terumat ma'aser. He should recite a blessing for each one individually. If he made all the separations one directly after the other without speaking in between, he should include them all in one blessing, [praising God who commanded us] "to separate the terumot and the tithes."58This applies if one sets aside terumah and tithes for his own produce. If he sets it aside for others, he should conclude the blessing "concerning the separation of tithes" (Hilchot Berachot 11:12-13).

זרעים הלכות מעשרות פרק א
Zeraim Maaser Chapter 1