What is an etrog? Here's what you need to know about Sukkot's famous citrus.

Here's another fruit to squeeze into your knowledge of the citrus family: etrogs. 

The yellow citron, commonly referred to by its Hebrew name, etrog, is a fruit used in the Jewish harvest festival of Sukkot, a holiday following Rosh Hashana, the Jewish New Year and Yom Kippur, the day of fasting and atonement. For one week of the year, etrogs are more prevalent than lemons, oranges and grapefruits in some communities, but what are they?

Etrogs are oblong yellow fruits, often four to six inches in length with a similar girth to an orange and a thick skin, more reminiscent of a pomegranate or grapefruit forgotten in the back of your crisper drawer for a few months too long than of a traditional lemon. 

Historical evidence shows etrogs are indigenous to India, which, along with other ceremonial plants dates back to 538 B.C. Scholars believe the etrog eventually migrated through Persia to Jerusalem, where it was and continues to be used in religious practice. 

Jewish people aren't the only ones to incorporate the etrog into religion. "India, in fact,  is believed to be the original home of the citron that then traveled to Persia and Babylon, where displaced Jews discovered and embraced the fruit, later taking seeds and cuttings with them back to Palestine," Mimi Sheraton wrote in Tablet magazine in October 2009. "And in India, Kuvera, the Hindu god of wealth, is always shown holding a citron in one hand." 

Growing etrogs is a tricky business, with the fruit-bearing trees being notoriously difficult to work with. "I found out that although I'm an expert citrus grower, I was not an expert etrog grower," Kirkpatrick told Tablet in October 2011. "It's easier to grow 2,000 acres of oranges or lemons than to grow one acre of etrogs." Arizonian Matt Bycer has also been trying to grow etrogs in Scottsdale, but after six years of cultivating 172 etrog trees, only three of them bear fruit. 

"They are hard to grow: Too much sun and they get skin burns, too little sun and they don't blossom, also mites love them," Patrick Ahern, a gourmet buyer at Baldor Specialty Foods explained in an email. "Scarred and blemished fruit are not permitted for use in the Jewish holiday so only the perfect ones can be used for that (and that is where the most profit comes from) and there are also many Jewish rules and regulations that need to be followed to make etrogs suitable for the holiday, including rabbinical supervision and strict growing standards, one of which forbids grafting onto other trees."  

So what does this finicky fruit taste like? Bitter, very bitter. 

Etrog recipes are almost as rare as the etrog tree itself, but some choose to turn the citrus fruit into jam or preserves, or they infuse vodka with etrog. No word on how a wedge of etrog works as a tequila chaser, but it can't hurt to try and find out, right? L'chaim!

With a pretty dismal skin to pulp ratio, the tart etrog is not the most practical fruit. Before sugar was popularized in medieval times, etrog, which is said to be one of the first citrus trees cultivated, was pretty much never consumed. Now, to be used in the Sukkot ritual, the etrog must be blemish free and have its stem intact, so it's not even eaten ceremoniously. Instead, etrogs are part of the four species of Sukkot, which also include a lulav (or palm branch), a hadass from the myrtle tree and aravah, the leaved branches from a willow tree. Together, all four are waved to all six directions while a prayer is said.