In general, when a forbidden food becomes mixed with a permitted food, it is batel be-shishim (rendered insignificant if the forbidden food constitutes less than one sixtieth of the mixture); in such small quantities, it does not contribute flavor. At the level of Torah law, ḥametz is also batel be-shishim. The Sages, however, ordained that even a drop of ḥametz render a permitted food forbidden when mixed with it. Even if the quantity of permitted food is a thousand or ten thousand times greater than the ḥametz, the entire mixture becomes forbidden.
The Sages added this stringency because the Torah itself is more stringent about ḥametz than other forbidden foods: 1) Generally, if one consumes a Torah-forbidden food, the punishment is malkot (lashes), but one who eats ḥametz incurs the more severe punishment of karet (extirpation). 2) Whereas all other forbidden foods may be kept in one’s home, ḥametz can neither be seen nor be found in our homes throughout Pesaḥ. The Sages therefore continued in this direction by establishing a safeguard: even if a drop of ḥametz falls into a food, it is forbidden to consume or derive benefit from it. 3) All other forbidden foods are prohibited throughout the year, and we are therefore accustomed to distancing ourselves from them, but since we eat ḥametz all year long, we are liable to forget that it is forbidden on Pesaḥ. The Sages, therefore, are more stringent about ḥametz, so that everybody remembers to be careful about it.
This law, that even a drop of ḥametz renders a mixture forbidden, goes into effect with the onset of Pesaḥ. Before Pesaḥ, ḥametz is batel be-shishim like all other forbidden foods. Although the prohibition against eating ḥametz and the mitzva to dispose of ḥametz go into effect at midday on the 14th of Nisan, the law that ḥametz is not batel be-shishim does not take effect until Pesaḥ begins, when one who consumes ḥametz incurs karet and when the prohibition of bal yera’eh and bal yimatzei take effect (SA 447:2).[1]
