About 400 years ago, many Jews living in Europe began to support themselves through the production and sale of whiskey. This was because the barons, the landowners, would often contract Jews to manage their affairs, and it was common for them to lease their distilleries and inns to Jews in exchange for a fixed price and/or a percentage of sales. This whiskey, which was made from barley and wheat, is considered ĥametz gamur. To prevent the great financial loss that would come each year with its disposal before Pesaĥ, it became necessary to sell it to a gentile before Pesaĥ and buy it back again immediately thereafter, in order to continue selling the whiskey as usual.
Over time, rabbinic leaders noticed that the sale was sometimes carried out improperly, leading to serious problems. If the sale is improper, the ĥametz remains in the possession of the Jew, and with every hour that passes he violates bal yera’eh and bal yimatzei. Additionally, it is forbidden to derive benefit from such ĥametz after Pesaĥ, and it must all be completely destroyed. Therefore, rabbinic authorities began to oversee the sale of ĥametz, in order to ensure its proper sale. Seeing that the sale was being carried out in an orderly manner, other Jews began to participate in the transaction, in order to save their own ĥametz from being lost. This is how mekhirat ĥametz began to spread and become increasingly common.
However, a number of prominent rabbis claimed that mekhirat ĥametz was not a real sale, but merely a fiction. In the first place, it is clear that after Pesaĥ the ĥametz will return to the Jew. Moreover, no sales tax is paid to the government on this sale. Thirdly, in a normal sale the buyer pays for all of the ĥametz and physically takes it into his possession, but here the gentile neither pays the full price, nor takes the ĥametz with him.
Nevertheless, the opinion of the vast majority of poskim is that mekhirat ĥametz may be relied upon and is as valid as any sale. By law, the gentile can refuse to sell the ĥametz back to the Jew after Pesaĥ. It is a bona fide sale, not a fiction. Nevertheless, in order to avoid even the appearance of a fiction, the rabbis made a practice of being very meticulous about all details of the sale. Since there are different halakhic opinions regarding the proper mode of purchase when a gentile buys from a Jew, the rabbis are careful to execute the sale using all forms of acquisition, so that it is clear that the sale is effective according to all opinions. In addition, they make sure that the sale is effective according to state laws as well (see MB 448:17, 19, and BHL ad loc.).
Regarding payment, a bill of sale is formulated to reflect the actual value of the ĥametz, and the gentile pays a cash deposit, as merchants are wont to do. The remainder of the sum is charged to him as a debt, but this does not prevent the completion of the purchase. After Pesaĥ, the gentile can decide: if he wants to keep the ĥametz, he must pay the debt; if he wants to sell the ĥametz back to the Jew, the Jew repays the cash deposit, and in return for the ĥametz, he pardons the gentile’s debt from before Pesaĥ. The reason no tax is paid on mekhirat ĥametz is that the king, or government, understands that this sale is carried out for religious, not commercial purposes, and therefore waives the tax.
In order to reinforce the sale, so that it resembles any other sale in which the buyer takes the purchased item into his possession, the rabbis ordained that the Jew sell to the gentile the ground on which the ĥametz rests, thereby transferring the ĥametz into the gentile’s possession (MB 448:12). In Eretz Yisrael, where it is forbidden to sell land to a gentile, the area is rented, and some poskim say that even outside Eretz Yisrael it is best to rent the area instead of selling it.