Beit Midrash

  • Pesach
To dedicate this lesson
Chapter Ten-Part Tow

Heavy and Light Libun: Does Temperature Affect Absorption?


Rabbi Eliezer Melamed

5.Heavy and Light Libun: Does Temperature Affect Absorption?
Heavy libun means heating a utensil by fire until any ĥametz taste in it is incinerated. One indication that libun has taken place is that the utensil undergoing libun becomes so hot that sparks fly from it when it is brought into contact with iron. Another indication is that its outer layer peels off, or that it becomes red hot.
Light libun means heating a utensil by fire to the point that a piece of straw or thread placed on the opposite side of the utensil becomes blackened from the heat. For example, to kosher a frying pan through light libun one must place the pan over fire and then put a piece of paper on the frying surface. When the paper starts to become scorched, the pan has been koshered.
Light libun is not effective where heavy libun is required, because the objective of libun is to incinerate any taste absorbed into the utensil, and this is only achieved through heavy libun. However, light libun is more effective than hagala because it is more capable than hagala at extracting the taste of ĥametz from the utensil, and apparently it can also incinerate some of the absorbed taste. Sometimes, when it is uncertain if libun is necessary, one may suffice with light libun. Light libun has another advantage as well: if a utensil has crevices that are difficult to clean, hagala cannot kosher it, since hagala removes the taste absorbed into a utensil but cannot render kosher the residual food stuck in its grooves. However, if one performs light libun and aims the fire at the grooves, the residual food will be incinerated, and the utensil will be rendered kosher. Light libun can be performed by putting a utensil in an oven and heating it at the highest temperature for about half an hour.
It is worth noting, however, that some poskim rule leniently that a utensil that has absorbed ĥametz via fire does not necessarily require heavy libun. In their opinion, the principle of ke-bole’o kakh polto applies to the temperature at the time of absorption. Thus, if a utensil absorbed the taste of forbidden food at a temperature of 300ºC, it can be koshered at the same temperature, and if the absorption occurred at 200ºC, it can be koshered at 200ºC, even though it does not become red hot or give off sparks at this temperature. According to these authorities, a cooking tray that absorbed a forbidden taste in an oven can be koshered in that oven at the same temperature as the absorption. The practical halakha follows the majority opinion, namely, that a vessel that absorbed taste via fire and reached a temperature beyond yad soledet must be koshered by heavy libun. However, in extenuating circumstances and when there are other reasons to be lenient, we take the lenient opinion into consideration. 5
It should be emphasized that absorption through fire can only happen while the food is being cooked by the fire on the flame. For example, if one cuts a baked good while it is on the burner, the knife absorbs the taste of the food through fire. However, if the baked goods were first taken off the fire and then cut, even if the baked goods are dry, the absorption is considered mild, and the knife may be koshered through hagala.
6.Koshering Vessels That Absorbed Ĥametz Prior to the Onset of the Prohibition
We have learned that if a utensil absorbs a forbidden food by means of fire, it must be koshered by fire. It is important to note that this principle applies only when non-kosher food has been absorbed. For example, if one roasts non-kosher meat on a skewer, the skewer must be koshered through libun, because the non-kosher food was absorbed by means of fire. However, if at the time of absorption the meat was kosher, and only later became non-kosher, the utensil may be koshered through hagala. To use a classic example, if a korban (Temple offering) was roasted on a skewer, and the meat of the korban later becomes notar (the sacrificial meat left over when the time to eat the korban ends, which must be incinerated and not eaten), the taste absorbed by the skewer is also notar and thus forbidden. The skewer may not be used until it has been koshered, but it is not necessary to perform libun. Hagala is sufficient because the skewer absorbed the taste of the meat while it was still permitted for consumption. 6
Accordingly, if one mistakenly baked meat and then dairy (or vice versa) in the same tray, the status of the tray depends on whether twenty-four hours elapsed between the baking of meat and dairy. If less than twenty-four hours elapsed, the baked food is forbidden because the flavor of meat mixed with the dairy food. The tray also absorbed forbidden taste, and thus heavy libun is required to kosher it. But if twenty-four hours elapsed, the taste of the meat became foul, and thus the dairy food may be eaten. Moreover, although the Sages rule that the tray must be koshered, hagala is sufficient, because it did not absorb any forbidden taste. In practice, since people are accustomed to putting such trays in the oven, the best thing is to kosher it through light libun, i.e., by putting it in the oven at the highest temperature for half an hour, for we have already seen that light libun is more effective than hagala. 7
The leading Rishonim disagree about whether the absorption of ĥametz during the year is considered the absorption of permissible matter, in which case baking trays can be koshered for Pesaĥ by means of hagala, or the absorption of forbidden matter. According to most poskim and SA 551:4, ĥametz has the status of forbidden food even though it is completely permissible throughout the year, since vis-à-vis Pesaĥ ĥametz is always considered forbidden and even before Pesaĥ it bears the name "ĥametz." According to this opinion, baking trays must be koshered via heavy libun. However, in extenuating circumstances and where there are other reasons to be lenient, the lenient position is occasionally relied upon (MB 451:28). 8
7.Utensils Likely to Be Damaged by Libun; Baking Trays
As we have learned, the objective of libun is to incinerate all taste absorbed into a utensil. To that end, the utensil must be heated to a very high temperature (more than 300ºC). There are two ways to tell that a vessel has reached such a temperature. One is that the utensil undergoing libun becomes so hot that sparks fly from it when it is brought into contact with iron. The other indication is that its outer layer peels off, or that it reddens completely.
However, some utensils are likely to be damaged by this process. It is forbidden to kosher such utensils through libun because we are concerned that, in an attempt to protect his utensil from damage, the owner will not perform libun properly. For example, it is forbidden to kosher an earthenware vessel that has absorbed non-kosher food or ĥametz, because libun is liable to crack the vessel. Nor is hagala effective on earthenware vessels because their unique composition causes them to absorb taste but not sufficiently release it. The only way to kosher an earthenware vessel is to return it to the kiln, where it is impossible to protect it from the full force of the kiln’s furnace. As a result, the vessel will either break and be lost or survive and be kosher (SA 451:1; MB ad loc. 13, 14).
Wonder Pots (an Israeli invention used for baking on stovetops) absorb taste though fire and therefore require heavy libun. However, since they are made of aluminum they cannot endure the libun process, and hence there is no way to kosher them for Pesaĥ (although if it was used to bake only simple cakes, one may be lenient and kosher it by means of hagala, as explained above in section 4).
Baking trays designed for domestic ovens become severely damaged by heavy libun. They lose their pleasant appearance and become warped to the extent that most people would no longer consider them usable. Therefore, they cannot be koshered through libun. There are, however, industrial baking trays that do not become seriously damaged by fire, and it is permissible to perform libun on such trays for Pesaĥ.
It is possible that one who knows that he will not care if his tray becomes warped and unattractive would be permitted, in time of need, to perform libun on such a tray. After all, every time libun is performed there is a risk of some damage, and the Sages only forbade libun where there is concern that the utensil will be completely ruined. When one will not be distraught if his baking tray is damaged, he may kosher it via libun. In practice, though, one should ask a competent authority what to do in this case. 9
^ 5.. The laws of light and heavy libun are discussed in SA and Rema 451:4 and in MB ad loc. (see R. Pfeiffer’s Kitzur SA, Basar Be-ĥalav vol. 2 ch. 12, and explanation 3 regarding the laws of light libun). However, it seems that according to R. Avigdor, cited in Hagahot Maimoniyot on MT, Laws of Forbidden Foods 17:5, light libun works just as well as heavy libun, but other poskim disagree. See Hagalat Kelim ch. 5 n. 3 that according to the accurate version of Hagahot Maimoniyot, even R. Avigdor agrees that light libun does not work like heavy libun.
SAH 451:16 and 19 states that in order to render the crevices in the frying pan kosher, one must aim the flame at them. See also Taz 451:8, which states that light libun causes the other side of the pan to reach the temperature of yad soledet bo, and see Piskei Teshuvot 451:18. The halakha does not follow this view; rather, light libun is when the pan reaches the temperature that would scorch a piece of straw on the other side of the pan, as Rema 451:4, MB 31 ad loc., and other Aĥaronim explain.
According to most poskim, a utensil that absorbed taste by fire requires heavy libun, even if the utensil itself only reached yad soledet bo. However, there are authorities who are lenient, as noted above. See Arugot Ha-bosem §119 and Minĥat Yitzĥak 3:66. See also Kitzur SA op. cit. explanation 5 and Piskei Teshuvot 451:17.
^ 6.. The basis for the distinction between utensils that absorbed permissible matter (heteira bala) and those that absorbed forbidden matter (isura bala) is explained in AZ 86a. The idea is that hagala releases most of the taste that is absorbed in the utensil. Thus, if the utensil absorbed forbidden taste, all of the taste must be eliminated from the utensil since the utensil became subject to a presumption (ĥazaka) of being forbidden. On the other hand, when the taste absorbed in the utensil was permitted at the time of absorption, there is no need to extract the weakened taste that remains after hagala. This distinction was subject to the discretion of the Sages since, after twenty-four hours, the taste absorbed in the walls of the utensil befouls the food instead of improving it and must only be extracted due to rabbinic injunction. Therefore, the Sages did not require this extraction when permissible taste was absorbed. According to this, we may only be lenient in a case of heteira bala once twenty-four hours have elapsed since the utensil absorbed the permitted taste. See also R. Pfeiffer’s Kitzur SA, Basar Be-ĥalav vol. 2 explanation 9 for an examination of other explanations.
^ 7.. This law is explained very well in R. Pfeiffer’s Kitzur SA, Basar Be-ĥalav vol. 2, ch. 2, based on Responsa Rama Mi-Fano §96 and Ĥatam Sofer YD §110. See also Kaf Ha-ĥayim 451:70, which lists the opinions and tended toward requiring light libun if it would not ruin the utensil, even though many authorities rule leniently that hagala is sufficient. See Kitzur SA (op. cit. ch. 12 nn. 7 and 10) for a discussion of the possibility of performing light libun in a pastry oven. It also seems that we can be lenient and allow light libun in an oven by factoring in the opinion that ke-bole’o kakh polto is a function of temperature, and the fact that the oven becomes an uncertainty about a rabbinic law after twenty-four hours. Thus, light libun koshers an oven even le-khatĥila.
^ 8.. See Hagalat Kelim, 7th introduction, which lists the opinions of the Rishonim in detail. Among the stringent opinions are: Rif, Rosh, Ran, and Rashba. Among the lenient opinions: Rambam, Rabbeinu Tam, and Or Zaru’a.
^ 9.. Pri Megadim explains (Mishbetzot Zahav §452) that one may perform libun on a utensil that might become partially damaged. Sidur Pesaĥ Ke-hilkhato 8:40 and Hagalat Kelim 5:6 and 13:315 state that one should not kosher baking trays using libun. Although it is possible to use baking trays that have undergone libun, most people nowadays prefer to throw them out. The question is whether the law is different for one who is unfazed by a warped baking tray (as per Pri Megadim). Perhaps someone whose baking tray became non-kosher – meaning that unless he koshers it he will have to throw it out anyway – may perform libun on it, for if he does not like the way it looks afterward he will simply throw it out. Some authorities rule leniently in this regard, but I am inclined to be stringent unless it is absolutely necessary. In extenuating circumstances, perhaps one may rely on Arugot Ha-bosem, cited in n. 5.
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