Although observance of the mitzvot of terumah and maaser was modified after the destruction of the Beit HaMikdash, the Holy Temple, it was not abrogated. These mitzvot apply to all fruits and vegetables grown by a Jew in Eretz Israel, and are practiced by Jews living in Israel and in the Diaspora. Those privileged to have a garden in Eretz Israel, as I do, get to do the mitzvot close up, and often get to perform the mitzvot while saying the designated brachot, blessings.
Start by harvesting as much produce as you desire, and lay it out in front of you. It is recommended to not move the fruit, except as outlined, before the end of the procedure.
For produce of the first, second, fourth, or fifth year following the Shmita, Sabattical, year, also lay a small denomination coin in front of you.
Once the produce is layed out before you. start by saying the following bracha. (*Important - If you have not harvested the fruit yourself, say the bracha only if you are sure no one has previously separated terumah and maaser.)
בָרוךְ אַתָה יי אֶלֹהֵינו מֶלֶךְ הָעולָמ אֲשֶר קִדֽשָנו בֽמִצֽותָיו וֽצִוָנו לֽהַפֽרִיש תֽרומות ומַעֽשֽׂרות
Next, separate slightly more than 1% of the produce from the rest and make the following three declarations in a language you understand:
With the exception of setting out the coin in the first, second, fourth
and fifth years, everything above is done regardless of the year of the
fruit. Now you have to choose how to proceed.
For produce of the third and sixth years after a Shmita year, make the following fourth declaration:
and you are done.
For produce of the first, second, fourth and fifth years after a Shmita year, do not make declaration 4a above. Instead say the following bracha:
בָרוךְ אַתָה יי אֶלֹהֵינו מֶלֶךְ הָעולָם אֲשֶר קִדֽשָנו בֽמִצֽותָיו וֽצִוָנו לִפֽדות מַעַשֵׂר שֵׁנִי
followed by declaration 4b:
Finally, lift up the coin and recite:
As of 2012, a one-shekel coin may be used 6 times. When the coin is "used up", it should be destroyed or defaced and discarded.
The separated produce may not be eaten. It should be disposed of repectfully. What exactly this means is not 100% clear to me. I think there is agreement you cannot simply put it uncovered in a garbage bin. According to my rabbi, it is possible to put it in a garbage bin immediately, after it has been placed in a plastic bag. I think other rabbis insist the produce be allowed to decay naturally until it is no longer edible. Among the things I don't know, is whether, for example, you could add it to a compost pile. I believe some machmir opinions may even require you to bury it.
Once the 1+% separated produce is placed somewhere where it won't be eaten, the remaining produce may be eaten and enjoyed by anyone.
None of the above, except for the eating part, may be done on Shabbat or the Jewish Festivals.
For food grown during the Shmita year, none of the above applies. A totally different set of rules, non-overlapping, apply.
I have tried to be as comprehensive as possible in putting down what I have learned about terumot and maasrot, but a number of questions remain.
Firstly: What do you do with the coin used to redeem maaser sheni when it is "used up"?
Secondly: It is not clear to me whether maaser sheni is 10% of the total produce, like maaser rishon, or only 9% (10% of the 90% that remains after maaser rishon has been given). I don't think this has any practical significance absent the Beit HaMikdash, since there is no actual transfer to Leviim or Kohanim.
A significant issue not addressed above is how to determine to which year the produce belongs. You must know this to determine whether the produce requires maaser ani or maaser sheni to be given. This is not a simple question, especially since I believe the answer is different for fruits and vegetables.
It is clear that the Shmita year starts on the first of Tishri, Rosh Hashana. And each subsequent year in the seven-year cycle presumably starts the same time. A complication is that the New Year for trees starts on Tu b'Shvat and not Rosh Hashana. For typical fruit trees, which bloom after Tu b'Shvat, considering the new year for trees as Tu b'Shvat rather than Rosh Hashana, makes no difference.
As is well known, fruit trees blossom, the blossoms are fertilized, and then they fall off, leaving a small fruit, which generally goes on to become a larger fruit, which then ripens and becomes edible. Halachikly, the year of fruit is determined from the time that the blossom falls off leaving the small fruit (this event is known in Hebrew as חנטה, Chanata).
If Chanata for a fruit occurs after Tu b'Shvat (the new year for trees), the year of the fruit is the year that started at Rosh Hashana. If Chanata occurs before Tu b'Shvat, the year of the fruit for maaser purposes is the year before the one that started at Rosh Hashana. The only tree I know of, for which this is important is the loquat (שֶסֶק).
In Israel, loquat trees blossom as early as Rosh Hashana, and Chanata occurs close to Tu b'Shvat. In Shilo, Israel, most years Chanata for the majority of the blossoms on my loquat tree occur before Tu b'Shvat.
Another fruit, besides the loquat, which is exceptional, is the אֶתרוג (etrog) or citron, where the year is determined by when it is harvested. This has signicant importance before and after the Shmita year.
All the above applies only to fruit from trees more than four years
old. Different halachot, laws, which have not been covered
here, apply to fruit from trees less than three years old (orlah)
or four years old (neta revai).