A Grafted Esrog
‘Passul When Missing Even a Tiny Bit’
Hybrid esrogim are a very serious concern, and one must be careful when choosing an esrog to ensure that it derives from a pure esrog tree. Today, most boxed esrogim come with a kashrus certificate, asserting that the esrog in the box is not grafted, the field in which the esrog grew has been in use for many generations, and is known to contain no mixture of other species.
Grafting Lemon Branches onto Esrog Trees
The esrog tree is known to be weak and have a short life span. Therefore, an esrog farmer may wish to graft branches from hardier lemon trees onto his esrog trees in order to produce a hybrid that is sturdier and more profitable. Fruits grown from such mixed species are often more beautiful than purebred esrogim.
Poskim question whether mixing lemons and esrogim transgresses the prohibition against planting or benefiting from kilayim. Since lemons and esrogim are so similar, combining them might not be included in the prohibition against mixing strains (see Shvus Yaakov 1:36, Chazon Ish, Kilayim 3:7). This article does not focus on whether making such a hybrid is permitted. Rather, we focus on whether this hybrid is kosher for use as an esrog on Sukkos.
Hybrid esrogim have been discussed by the most prominent poskim of the last 400 years. Numerous teshuvos have been written by the Rema, Maharam Alshich, Mabit, R’ Betzlalel Ashkenazi, and many others. The conclusion of all these poskim is that a hybrid esrog is passul.
A Hybrid Esrog Is Not an Esrog
Several explanations have been offered as to why hybrid esrogim are passul. The most commonly cited reason is that “a hybrid esrog is not an esrog at all.” In other words, the Torah requires us to use an esrog on Sukkos, not a combination of an esrog and another fruit (Teshuvos Rema, 117, Magen Avraham 648:27, Mishnah Berurah, s.k. 65).
Distinctive Traits of an Esrog
A pure esrog has certain traits that distinguish it from a hybrid. The stem of a hybrid esrog juts out from the bottom, whereas a pure esrog’s stem grows from an indentation on the bottom. The skin of a hybrid is smooth, whereas that of a purebred esrog is bumpy. The inner white flesh of a hybrid is thin like a lemon’s, whereas a pure esrog’s flesh is thicker (see Mishnah Berurah, ibid.). Nonetheless, the Mishnah Berurah cites the Chasam Sofer who rules that one may only use these signs to deem an esrog passul. One can’t rely on them to determine that an esrog is pure. When buying an esrog, one must only choose one grown in an orchard known to be of pure lineage (see Shaar HaTzion, s.k. 74).
With recent technological advances in horticulture, it is now possible to subject a fruit to laboratory tests, and thereby determine its genetic makeup. Is such a test sufficient to deem a certain, unknown breed of esrogim pure and kosher? Rabbi Yechiel Michel Stern, a contemporary expert on esrogim, consulted with other experts in the field and came to the conclusion that even pure and kosher esrogim have some genetic traces of lemons. Therefore, genetic testing is useless to definitively determine which esrogim are kosher (Kashrus Arbaas Haminim, p. 181). How is it that pure esrogim, which have never been grafted with lemons, somehow show traces of lemon?
The esrog plant produces its fruit by means of pollination. Bees carry pollen from the stamens to pistils, causing fruit to grow. However, bees might also happen to carry pollen from the stamens of lemon flowers to the pistils of esrog flowers, thus effecting a cross-pollination of the two species. The resultant fruit carries traces of both parents.