Etrog, (Ashkenazi pronunciation: esrog) is the Hebrew name for the citron or Citrus Medica.
It is one of the four species used in the rituals associated with the Jewish holiday of Sukkot. The others are the lulav (date palm frond), hadass (myrtle), and aravah (willow branch).
Leviticus 23:40 refers to the etrog as pri eitz hadar, which literally means, "a fruit of the beautiful tree." In modern Hebrew, pri hadar refers to all citrus fruit, while Nahmanides comments that it originally referred to the citron only. Over time, the word etrog was introduced, adapted from the Aramaic. The Arabic name for the fruit, itranj, mentioned in hadith literature is also cognate with the Hebrew.
The Etrog is typically grown from cuttings that are two to four years old; the tree begins to bear fruit when it is around four years old. If the tree germinates from seeds, it will not fruit for about seven years, and there may be some genetic change to the tree or fruit in the event of seed propagation.
Dimensions and shape
The fruit is ready to harvest when it is six inches long. It is typically picked while still green.
According to Halakha, the Etrog used in the mitzvah of the four species must be largely unblemished and of a nice form and shape. Extra special care is needed to cut around the leaves and thorns which may scratch the fruit. Also, the bearing branch should be curved in order to get the fruit growing in a straight downward position. Otherwise, the fruit will be forced to make the curve on its own body when turned downwards because of its increasing weight.
Some Hasidim look for an Etrog with a gartel- an hourglass-like strip running around the middle. According to researchers, this gartel indicates that the tree was infected by a certain virus or viroid that decreases the albedo on the specific spot. These viroids has been around since the time of Bar Kokhba, and archeologyists have unearthed a mosaic depicting an Etrog with a gartel.
Only the Etrog was found to be susceptible to these viroids, proving that the Etrog is genetically pure, and has not changed much over the centuries.
An etrog that still has a pitom at its tip (a pitom is composed of a style called in Hebrew "dad", and the stigma which is called shoshanta, and it usually falls off during the growing process) is considered especially valuable. However, those varieties that shed their pitom during growth just like other citrus species ? are also kosher. When only the stigma break off even post harvest, it could still be considered kosher as long as part of the style is remained attached.
Many Pitom's are preserved today thanks to an auxin discovered by Dr. Eliezer E. Goldschmidt, professor of horticulture at the Hebrew University. Working with the Picloram hormone in a citrus orchard one day, he discovered to his surprise that some of the Valencia Oranges of nearby had preserved beautiful, perfect Pitom's.
Usually a citrus fruit besides an Etrog or citron hybrid like the Bergamot, does not preserve its Pitom. When it occasionally does, it should be at least very dry and intended to break. In this case the Pitam's where all fresh and healthy just like those of the Moroccan or Greek citron varieties.
Experimenting with the Picloram in a laboratory, Professor Goldschmidt eventually found the correct “dose” to achieve the desired effect: one droplet of the chemical in three million drops of water. An invention which is highly appreciated by the Jewish community.
Grafting and Breeding
A general DNA study was arranged by the world known researcher of the etrog, Pro. E.E. Goldschmidt & colleagues, who positively testified 12 known accessions of citron for purity and being genetically related. This is all about genotypeic classification which could be changed by breeding for e.g. out cross pollination etc., not about grafting which is not suspected to change any genes.A brief documentation of this study could be found at the Global Citrus Germplasm Network.