Like the Torah which is kept safe in the holy ark, the Etrog is kept safe in special Etrog box. This one from Raphael Carl is constructed from walnut and aluminum.
The etrog is a Citrus fruit of a tree of the orange and lemon family. It is oblong in shape, and sometimes as much as six inches in length. The skin is thick, somewhat hard, fragrant, and covered with protuberances; the pulp is white and subacid. Modern naturalists assume the north of India to be its native home; but it passed to the countries of the Mediterranean from Media or Persia ; hence the name of the tree, "Citrus medica," and of the fruit, "Malum medica," or "Malum Persica". It is possible that the Jews brought the tree with them from Babylonia to Israel.
Not just any etrog can be used during sukkot... there are rules (aren't there always???). So what makes a Kosher Etrog?
Esrog must be shaped "like a tower"--its bottom larger than its top.
Pitom, the flowered blossom at the tip of the fruit, and Uketz, the stem which is sunk into the broad base, must be examined carefully to make sure that both are present and intact.
If the Pitom falls off or is broken during Sukkot, a rabbi should be consulted. To avoid this problem, many people prefer to use Esrogim which grow without Pitoms.
The Pitom should be directly in line above the Uketz
While the etro is used symbolically... it can be used in recipes as well, similarly to other citrus fruits.
Citron [Etrog/Esrog] Slices Cooked in Syrup
4 large citrons (lemons, oranges, tangerines or etrog)
5 cups (1 kg) sugar
2 cups (500 mL) water
Juice of 1/2 lemon
Wash the citrons / etrog and leave them to soak in cold water for at least 3 hours. Then cut them into thick slices (about 1/3 inch (1 cm)) and remove the seeds.
Put the sugar, water, and lemon juice in a large pan and bring to the boil. Put the citron slices in, pressing them down into the syrup. Put the lid on and simmer gently for 1-1 1/2 hour, or until they are very soft. Lift out the slices and arrange on a serving dish. Reduce the syrup by simmering, uncovered, until it has thickened enough to coat a spoon, and pour a little over the slices. (Leftover syrup can be kept in a covered jar.)
This makes a most delicious and easy dessert to serve as an accompaniment to a citrus cake or a plain rice pudding. It surprises everyone. This recipe is from Tunisia and Morocco, but it is also made by Jews in Italy. You can serve the slices sprinkled with a little cinnamon and chopped pistachios and with a dollop of cream.
You can learn more about the Etrog and Sukkot and more yummy recipes right here.