Nat bar Nat and Prohibited Foods
Regarding food, there is a general principle in halacha called ta’am k’ikar, the taste is equivalent to the main substance. This principle draws equivalence between the taste of a food and the actual food within the context of both prohibitions and positive commandments. Thus, a Nazir, who is prohibited from drinking wine, may not eat bread that has absorbed the taste of wine. Similarly, one may use matza made from a mixture of rice flour and wheat flour for the mitzvah of eating matza, as long as the taste of wheat is recognizable.
With regard to the prohibition of basar b’chalav (meat and milk), the Talmud introduces an important caveat:
הלכתא דגים שעלו בקערה מותר לאוכלן בכותח.
“The halacha is that fish which absorbed taste from a meat bowl may be eaten with kutach (a dairy dip).”
The Talmud establishes that if fish absorbs taste not from a piece of meat itself but from a bowl that had absorbed the taste of meat, it may be eaten with dairy. The rationale for this leniency is provided earlier in the Gemara. Shmuel explains that the taste of meat which is absorbed in the fish is only a secondary meat taste and can therefore be combined with dairy. Since the meat taste in the fish is twice removed from the meat – from the meat to the bowl and then from the bowl to the fish – we do not employ the rule of ta’am k’ikar. Rather, we view the meat as notein ta’am bar notein ta’am (nat bar nat), something which imparted secondary taste, which does not cause the resultant food to have the same status as the meat.
It is important to note that the Talmud invokes the leniency of nat bar nat specifically with regard to the prohibition of basar b’chalav. Basar b’chalav is a unique prohibition in that each constituent component (meat and milk) by itself is totally permissible; only when the two ingredients are combined is the prohibition created. Thus, when we find a special leniency in the realm of basar b’chalav, it is far from a given that the same leniency would apply to other prohibitions. We must therefore wonder: Does the leniency of nat bar nat apply to other prohibitions outside of the world of basar b’chalav? For example, if animal blood, the consumption of which is a Torah prohibition, is cooked in a pot and then fish absorbs taste from that pot, is the fish permitted to be eaten because it has only acquired secondary blood taste?
The answer of virtually all Rishonim is an emphatic no: The leniency of nat bar nat applies only to basar b’chalav and not to other prohibitions. The Ran and Rashba explain the rationale behind this distinction as being that it is necessary to distinguish between creating a new prohibition and maintaining a preexisting prohibition. In order to create the prohibition of basar b’chalav, it is necessary to mix a primary taste of meat with a primary taste of milk. If either the taste of meat or milk is only a secondary and therefore weakened taste (ta’am kalush), the mixture does not meet the minimum requirements to create the prohibition. However, once a prohibition has already come into existence, weakening its taste does not permit it. Thus, the secondary – or even tertiary, and beyond – taste of an already established prohibition remains prohibited.
Nat bar Nat and Chametz
What is the status of secondary taste with respect to chametz before Pesach? Can we apply the leniency of nat bar nat in this case? On the one hand, chametz before Pesach is entirely permissible to eat, which makes it comparable to the taste of milk or meat. This would imply that if chametz is reduced to secondary taste before Pesach, e.g., in the case of a food cooked in a utensil previously used to cook chametz, it would be permissible for consumption on Pesach, as per the leniency of nat bar nat. On the other hand, perhaps chametz is more similar to standard prohibitions, for which there is no leniency of nat bar nat, since when Pesach begins, chametz becomes intrinsically prohibited and does not depend on any further mixture, as does milk or meat. This would imply that chametz is prohibited on Pesach even if it is reduced to secondary taste before Pesach. To phrase the question differently, what is the precise definition of “issur” (prohibition) to which nat bar nat does not apply?
To shed light on this question, we turn to the topic of hechsher keilim, purifying utensils which absorbed non-kosher taste, in which there is a similar distinction between absorption of heter (permissible foods) and issur (prohibited foods), and the ensuing discussion in the Rishonim regarding to which category chametz belongs.
Hechsher Keilim: Issura Bala vs. Heteira Bala
The Mishna rules that one removes non-kosher taste from a utensil (and thereby renders it kosher) in the same manner that it absorbed non-kosher taste. If it absorbed non-kosher taste through contact with a hot liquid, it is made kosher via hagala, submersion in boiling water; if it absorbed non-kosher taste through direct exposure to a flame, it requires libbun, heating the utensil with a direct flame until the outer layer burns away. Thus, according to the Mishna, a spit or grate, which absorb non-kosher taste through direct exposure to a flame, are made kosher via libbun.
However, the Gemara points out that this ruling contradicts another Mishna that states that a spit or a grate which absorb taste from meat of korbanot will later – after the allotted time to eat the korbanot has expired – only require hagala in order to cleanse the walls of the utensils from notar, korbanot that have not been consumed within the prescribed time. The Gemara resolves the contradiction by distinguishing between issura bala, an absorption of prohibited food, and heteira bala, an absorption of permissible food. Since at the time of absorption the korbanot were permitted to be eaten, they are considered heteira bala and only require hagala. The first Mishna, on the other hand, refers to a spit or grate that absorbed non-kosher taste (issura bala) and therefore requires libbun.
Based on this Gemara, the Ra’avad writes that if a utensil absorbs chametz before Pesach even through direct exposure to a flame, hagala is sufficient to make the utensil kosher for Pesach. He explains that since chametz before Pesach is entirely permissible, the case can be labeled as heteira bala and hagala therefore suffices. According to the Ra’avad, determining whether a case is an instance of issura bala or heteira bala is simply a matter of ascertaining whether the food was permissible or forbidden at the time of absorption.
This literal approach to the definition of issura bala and heteira bala gives rise to a basic question. What is the logic behind the distinction between heteira bala and issura bala? If hagala suffices to remove that which was absorbed through direct flame, why shouldn’t it remove such absorptions (beli’ot) across the board, even in cases of issura bala? Conversely, if hagala does not successfully remove that which was absorbed through direct flame, how does it suffice to make utensils kosher in cases of heteira bala?
The Ramban argues with the Ra’avad and offers an alternative explanation. In reality, hagala is effective in removing the majority, but not all, of the beli’ot from a utensil that absorbed through direct flame. To understand the distinction between issura bala and heteira bala, a redefinition of terms is necessary. Issura bala refers to a situation in which at the time of absorption the food already had its ultimate status (shem). Heteira bala, in contrast, refers to a case in which the status of the food changes after the point of absorption. When a utensil absorbs the taste of korbanot meat, it is considered heteira bala because the meat is originally absorbed with the status of korban and only later – when the allotted time for the korban elapses – does it gain the status of notar. This is significant because the new status of notar, according to the Ramban’s novel interpretation of the Gemara, is only conferred upon the majority of the beli’ot, those that can be removed via hagala; the absorptions that remain in the utensil even after hagala never achieve the status of notar. Thus, in a case of heteira bala, after hagala is performed, all beli’ot that are prohibited have been removed and the remaining beli’ot are permissible, never having attained the status of prohibition in the first place. In cases of issura bala, however, even though most of the prohibited beli’ot will be removed via hagala, the remaining beli’ot which are not removed through hagala continue to render the utensil non-kosher, as these beli’ot are still forbidden.
The Ramban writes that according to his definitions, chametz belongs to the category of issura bala. This is because at the time of absorption, the food already has the status of chametz (the chametz happens to be permissible at that time because it is not yet Pesach; its status of chametz, however, is already present). Thus, when Pesach comes and the prohibition of chametz comes into effect, all beli’ot with the status of chametz, both those that can be removed via hagala and those that cannot, become prohibited. Hagala will therefore not purify a spit or grate that absorbed chametz, firmly placing chametz in the category of issura bala.
The consensus of the poskim is to treat chametz as issura bala like the Ramban. For example, the Rif codifies the Mishna that requires libbun for utensils that absorb through direct exposure to a flame in the context of Hilchot Pesach. The Ran infers from this that the Rif agrees with the Ramban and would require libbun for such a utensil even if it absorbed chametz. The Pri Chadash writes that the same inference can be made from the Rosh’s inclusion of this halacha in Hilchot Pesach. Indeed, the Shulchan Aruch rules in accordance with the Ramban that any utensil that absorbed chametz through a direct flame requires libbun.
From the examination of the laws of hechsher keilim, it seems generally agreed upon that chametz before Pesach, despite being permissible for consumption, is nevertheless regarded as issura. If so, this would imply that the leniency of nat bar nat, which as discussed previously does not apply to items with an issur status, would not apply to chametz. However, further examination of the laws of hagala on Erev Pesach reveals that this conclusion is not necessarily accurate.
Hagala on Erev Pesach
The goal of hagala is to expel the non-kosher taste from the walls of the utensil by means of submerging the utensil in boiling water. Inherent in every attempt at hagala, though, is a vexing paradox: The utensil expels the non-kosher taste into the boiling water, but is then sitting in a solution of boiling water and non-kosher taste, a ripe environment for re-absorption of the non-kosher taste. How can one purify the utensil without it being contaminated again immediately thereafter?
There are two main solutions to preventing the re-absorption of the non-kosher taste. First, one may submerge the non-kosher utensil in boiling water equal to sixty times the volume of the utensil, ensuring that any non-kosher taste which exits the walls of the utensil is immediately nullified by the water. Second, one can wait twenty-four hours before initiating the hagala process, ensuring that any taste which exits the utensil is pagum, stale, such that its re-absorption is insignificant.
The Rosh writes that if one is careful to perform hagala for chametz utensils on Erev Pesach prior to five hours into the day (the point at which chametz becomes rabbinically forbidden), one need not be concerned with employing one of the above solutions. He reasons that any re-absorption of the chametz will only be secondary taste and because chametz before five hours into the day is permissible to eat, the utensil will remain kosher based on the leniency of nat bar nat. The Rosh’s ruling is codified by the Shulchan Aruch. It is apparent that the Rosh and Shulchan Aruch hold that chametz is considered heteira such that the leniency of nat bar nat is relevant to chametz.
Many Acharonim object to this ruling of the Rosh and Shulchan Aruch, claiming that it contradicts their earlier ruling requiring libbun in order to purify a utensil that absorbed chametz through a direct flame. That ruling assumes that despite the fact that chametz is permissible to eat before Pesach, since the status of chametz is ever-present, it falls under the category of issura. If so, how can the Rosh and Shulchan Aruch simultaneously maintain that the leniency of nat bar nat is applicable to chametz before Pesach, which assumes that chametz is regarded as heteira? This question forces these Acharonim to conclude that even when one performs hagala prior to the fifth hour on Erev Pesach, one must still ensure that there is enough water to nullify the chametz taste or that the utensil has not absorbed chametz within twenty-four hours of the hagala.
Defense of the Rosh and Shulchan Aruch: Significant and Insignificant Chametz
Those bothered by the contradiction in the Rosh and Shulchan Aruch assume that the definition of “issura” is uniform throughout. Namely, if chametz is considered issura in the realm of hechsher keilim, it must also be considered issura in the realm of nat bar nat. It is thus inconceivable to on the one hand require libbun in order to remove beli’ot of chametz from a utensil which absorbed through a direct flame and on the other hand permit secondary taste of chametz based on nat bar nat. The Rosh and Shulchan Aruch, however, clearly did not see any contradiction between these two positions. What was their logic? How can their position be defended?
The Chazon Ish provides an explanation that resolves the contradiction. The operating principle is that when the prohibition of chametz takes effect at the beginning of the fifth hour on Erev Pesach, all significant chametz becomes prohibited. Thus, in both the cases of hechsher keilim and nat bar nat, the question of crucial import is whether the chametz that is in existence at the beginning of the prohibition is considered significant. Regarding hechsher keilim, since the beli’ot that are not removed via hagala have the ever-present status of chametz and are in no way diminished, they are considered significant enough for the prohibition of chametz to take effect on them. The prohibition of chametz will certainly forbid a small amount of potent chametz. It is therefore necessary to perform libbun in order to remove those beli’ot to make the utensil kosher. However, regarding nat bar nat, since the taste has been diminished to the point of ta’am kalush, this taste is considered insignificant and impotent, and the prohibition of chametz therefore does not forbid it. To put it succinctly, the beli’ot which remain in a spit or grate after hagala are quantitatively diminished, but qualitatively undiminished, whereas secondary chametz taste is quantitatively undiminished, but qualitatively diminished. The prohibition of chametz will take effect on all significant chametz, however little in quantity, but will not forbid insignificant chametz, even in large quantities. Thus, it is possible for chametz to be included in the category of issura with regard to Hechsher Keilim and be included in the category of heteira with regard to the leniency of nat bar nat.
 The Rishonim dispute whether this principle is biblical or rabbinic in origin. See Beit Yosef, Y.D. 98.
 Pesachim 44a-b, as per Bamidbar 6:3.
 Challa 3:7 and Shulchan Aruch, O.C. 453:2
 Chullin 111b
 See, however, the opinion of “yesh chochechim lehakel” rejected by Meiri, Chullin 111b.
 Chullin 41a in the pagination of the Rif
 Teshuvot HaRashba 1:516
 See also Hagahot Rabbeinu Peretz 6 to Semak 213 for an alternative rationale as to why nat bar nat does not apply to other prohibitions.
 Avoda Zara 75b
 Avoda Zara 76a; see also Yerushalmi, Avoda Zara 5:15
 Avoda Zara 76b
 Zevachim 97a
 Quoted in Ramban, Avoda Zara 76a
 Avoda Zara 76a
 Pesachim 8b
 Commentary on Rif, Pesachim 8b and cited by Beit Yosef, O.C. 451
 O.C. 452
 Pesachim 2:7
 O.C. 451:4
 Pesachim 2:7
 O.C. 452:1
 Pri Chadash 452, Bi’ur HaGra 452:1, Bi’ur Halacha 452:1, s.v. she’ein
 O.C. 119:14