Kashering Plastic Food Utensils

I.      Introduction

 

     We find in the Torah specific guidelines as to how to "kasher" utensils made from materials that were in use in Biblical times (e.g. metal, earthenware etc.).  Many materials, however, including, of course, those which were developed only later, were not addressed by the Torah.  On what basis, then, do we determine the status of these materials with respect to kashering?  How did Chazal determine the procedure for kashering utensils made from materials not discussed in the Torah?

This shiur will explore the various directions taken to determine the halakha for newer materials, such as rubber or the different types of plastic.  This topic has been approached by recent poskim based primarily on the decisions of commentators on the Shulchan Arukh.  We will attempt to examine the issue based on concepts and precedents raised in the Gemara and Rishonim.

 

II. Background - Source of Hekhsher Keilim

 

     Upon Benei Yisrael's return from their successful military campaign against Midyan, Elazar (the kohen gadol) outlined the instructions concerning the utensils brought back as spoils of war:

 

 "This is the ordinance of the Torah that God commanded Moshe: Only the gold and the silver, the brass, copper, the iron, the tin, and the lead, everything that passes through fire, you shall pass it through fire and it will be clean… And all that does not pass through fire you shall pass through water." (Bemidbar 31: 21-27)

 

This basically outlines the halakhic process of kashering food utensils.  Had it been for the pasuk alone, one might have viewed the act of kashering as a "matir," a purely ceremonial act transforming a forbidden utensil into a permissible one, that has no physical effect upon the residual ta'am (flavor) of non-kosher food absorbed into the utensil.  One would be required to do this act solely in order to fulfill the Torah's requirements and render the vessel useable.  The Mishna and Gemara, however, indicate otherwise:

 

"One who purchases utensils from a non-Jew - that which is normally immersed, he should immerse; [that which is normally] purged/boiled, he should boil; [that which is normally] heated over direct fire, should be heated over direct fire."

(Mishna, Avoda Zara 75b)

 

     It emerges from the Gemara's discussion that the process of hag'ala (boiling) works under the halakhic assumption of "ke-bol'o kakh polto" – as it was absorbed [into the utensil's walls], so it is expelled [from the walls].  Thus, if ta'am from non-kosher food was absorbed as a result of boiling, then immersing the vessel in boiling water will extract any ta'am that could ever potentially leave the walls.[1]  Libun (dry heating), on the other hand, works differently.  Rather than extracting the ta'am from the utensil, the intense heat destroys the ta'am in situ.[2]

 

     The aforementioned pasuk in Bemidbar (31:21) mentions the procedure for kashering gold, silver, brass/copper, iron, tin and lead.  In Vayikra 6:21, in discussing the laws of the korban chatat, the pasuk states: "The earthen vessel in which it is boiled shall be broken, and if boiled in a brass/copper vessel, it shall be purged and rinsed with water."

 

     The gemara explains why the Torah did not sanction hag'ala for earthenware vessels:

 

"The Torah testified upon earthen vessels, that they never [fully] emit [the absorbed ta'am] from their walls." (Talmud Bavli, Pesachim 30b)

 

In our translation of this passage, we added the word "fully" to indicate that earthen utensils do, in fact, emit taste from their walls, but some degree of taste will always remain.  The Mordekhai (ad loc. 563) comments:

 

"There is no takana [possibility of rectification] for an earthen vessel through hag'ala.  We do not say 'just as it did not emit [ta'am] during hag'ala, similarly it won't emit [ta'am] during cooking use,' because it is possible that even though it did not emit during hag'ala, it will emit during subsequent cooking use."[3]

 

Since cheres (earthen) utensils do emit ta'am during the cooking process, they may not be used after absorbing non-kosher ta'am.  On the other hand, since the ta'am will never fully leave the utensil's walls, such a utensil does not have the possibility of kashering.

 

III. Materials not mentioned by the Torah

 

     What is the status of materials not mentioned in the Torah?  Would they be classified as metals, which have the possibility of kashering, or like earthen vessels, which cannot be kashered?

 

     A priori, we might employ one of four approaches in classifying these materials:

 

A. We determine a given material's status based on its physical properties.  We must ask questions such as: Does it absorb ta'am?  Does it react to hag'ala or libun like metal or like earthenware?  Such a test would not require an advanced laboratory.  One could simply boil water in the kashered pot and taste the water to see if it emits a significant amount of residual ta'am.

 

B. Alternatively, we might claim that if the new material is composed of materials that the Torah mentioned, it should follow the rules that the Torah delineated for those components.

 

C. A third approach would be textual, rather than scientific.  As we saw, in Bemidbar the Torah lists various materials that can be kashered, and in Vayikra it establishes that while copper/brass is kasherable, earthenware is not.  This might indicate that generally, utensils have the possibility of kashering, and earthenware marks an exception.  This indeed might be the implication of the Gemara: "The Torah testifies upon earthen vessels that they never [fully] emit [the absorbed ta'am] from their walls."  Earthenware is the exception.  Any other material, unless proven otherwise, is kasherable.

 

D. Lastly, one might discount all the above approaches and choose not to rely on any scientific observations of the given material's properties, and not to recognize any default status of "kasherability."  This approach would argue that unless the Torah explicitly informs us of the procedure for kashering utensils made from a given material, we cannot take the liberty to establish such a procedure.  Therefore, we must assume that all materials that the Torah does not mention resemble earthenware and do not have the possibility of kashering.

 

     Having delineated the four theoretical approaches to dealing with this issue, let us now examine how the Gemara and Rishonim dealt with several examples of such materials.  As we study the relevant sources, we will try to determine which of the above four approaches were employed.

 

Wood

 

     The most prominent example of a material not addressed by the Torah is wood.  The Gemara in Masekhet Pesachim (30b) states very simply, "Rav Huna son of Rabbi Yehoshua said: The wooden ladle of a pot ('etz ha-parur'[4]) must be purged with boiling water and in a 'keli rishon' (a pot that was boiled on the fire)."  The gemara adds: "He (Rav Huna) held 'ke-bol'o kakh polto'."  From the context of the Gemara it is clear that Rav Huna is concerned primarily with the manner in which this particular utensil was normally used, and not the fact that it was made of wood.  The Gemara appears to take for granted the possibility of kashering wood, despite the fact that the Torah makes no mention of wood when presenting the laws of kashering.  With the exception of Rashi, all the Rishonim record this ruling of the gemara as the clear, definitive halakha, without commenting as to the origin of, or reason behind, Rav Huna's assumption that wood is kasherable.[5]

 

     On what basis did Rav Huna make this assumption?  Why did the Rishonim accept this assumption without comment?

 

     One possibility is that they tested wood utensils and found that they can, indeed, be successfully kashered.  The "testing" approach assumes that the Torah requirement of kashering is not merely a ceremonial requirement, but rather stems from the physical realities of absorbed ta'am and its behavior.  We might support this assumption on the basis of four factors:

 

A)   The Torah differentiates between utensils used with heat and those used with cold, indicating that the process of kashering depends on the physical properties of the given utensil;

B)   Similarly, the mishna instructs us to kasher utensils based on their use (i.e. boiling water or intense dry heat);

C)   The Gemara explicitly establishes the principle of "ke-bol'o kakh polto";

D)   The Gemara attributes the Torah's disallowing of kashering earthenware to the fact that the material does not sufficiently release its absorbed ta'am during kashering.

 

Accordingly, we might assume that the Gemara and Rishonim accepted the possibility of kashering wood on the basis of empirical evidence to wood's ability to satisfactorily expel previously absorbed ta'am.

     Alternatively, we might invoke the textual approach mentioned above as the reason for assuming the possibility of kashering wood.  Since the Torah singled out only earthenware as a material that cannot be kashered, we may assume that all other materials are kasherable.

 

     Rashi[6] is the only Rishon (to the best of my knowledge) who brings a textual source for Rav Huna's assumption.  He writes, "For regarding wood and metal utensils it is written 'yishatef'; 'u-morak ve-shutaf'," whereas for earthenware utensils the Torah requires breaking them ("yishaver" – "it shall be broken").  Without trying to explain Rashi's limud[7], we will simply point out that he saw the need for a limud to justify the assumption that wood is kasherable.  Otherwise, in Rashi's view, we would not allow kashering wood.  Rashi appears to have accepted the final possibility we mentioned, namely, that there is no presumed status of kasherability, and we cannot rely on experimentation.  The silence of other Rishonim regarding this Gemara suggests that Rashi is alone in this view.

 

     Interestingly, the materials we will now discuss were not explicitly addressed by the Gemara, which left it to the Rishonim to determine their status with respect to kashering.

 

Stone

 

     Three opinions exist as to the status of stone vessels. 

 

a) The first approach follows the line of reasoning adopted by most Rishonim regarding wood, as we saw earlier.  Namely, either through experimentation or because of their textual understanding that only earthenware was singled out as non-kasherable, some Rishonim allow kashering stone.  But here, too, most Rishonim who classify stone with metal[8] and allow kashering do not reveal a source or reasoning.

 

b) Rav Hai Gaon[9] felt that stone has the same status as earthenware.  His reasoning, however, is not recorded.  He might have experimented and found stone to have similar properties to earthenware.  Or, he perhaps reasoned that the origin of stone, the earth, renders it halakhically similar to cheres (earthenware).  Needless to say, this approach would have to explain why this status is not conferred upon metal, which also comes from the ground!

 

c) The Ri Malki Tzedek[10] holds that stone does not absorb ta'am.  This is the most novel of the three positions, though it is based on the Tosefta in Zevachim[11] which states, "Stone vessels… do not require purging, but only 'hadacha' (rinsing)".[12,13]

 

     What logic underlies this position?  The only possibility that comes to mind is experimentation.[14]  Whatever the reason, we can conclude from all opinions regarding stoneware other than Rav Hai Gaon's, that we DO NOT assume a "new" material to be unkasherable until proven otherwise; we do not require a source to classify a given material as kasherable.  (Indeed, commonly accepted halakha allows treating stoneware like metal.)

 

Bone

 

     The halakhic classification of bone utensils is not mentioned in the Torah or the Talmud, despite the fact that these utensils were widely used during those periods.  Two directions exist among the Rishonim regarding the status of bone utensils:

 

a) Most opinions hold bone to be kasherable, like metal[15].  However, some Rishonim within this group maintain that one should nevertheless refrain from kashering bone utensils, due to the concern that the owner will not purge it properly for fear of damaging it.[16]

 

b) Rav Yechiel of Paris[17] is quoted as having issued the following ruling: "Regarding a bone vessel we find no beli'a (absorption of ta'am) or issur."  This cryptic citation lends itself to two interpretations.  Rav Yechiel perhaps meant that we have no source indicating that bone absorbs ta'am.  If so, then Rav Yechiel here insinuates that we never assume any substance to be capable of absorbing ta'am unless we find an explicit source to this effect.

 

     We opened our discussion with four a priori approaches to classifying materials omitted by the Torah.  The first two involved the physical properties of the material, whereas the last two seek to categorize by default.  But in light of this understanding of Rav Yechiel of Paris, we now have a fifth possibility.  The very omission of a material from the Torah's discussion, despite its use at the time of Matan Torah, might indicate that it simply does not absorb or emit ta'am.  Although wood is also omitted, Chazal observed the fact that it does emit ta'am.  Although Rav Yechiel invokes this rule specifically in the context of bone, it may very well apply to stone and glass, as well.

 

     Alternatively, Rav Yechiel might have meant that in observing the physical attributes of bone, we have found that it does not absorb.

 

     What is most striking is that none of the Rishonim adopted the stringency of classifying bone as earthenware given the absence of guidelines in the Torah and Talmud.

 

Glass

 

     The last material we will survey is glass.  While the Torah does not address the status of glass, it is dealt with in the Talmud.  Surprisingly enough, however, these Talmudic discussions do not directly relate to kashrut. 

 

We find three different views in the Rishonim regarding the status of glass with respect to kashering:

 

a) The Mordekhai (Pesachim 374) states: "Rabbenu Yechiel of Paris would say that these glass cups used for drinking during the year may not be used for drinking on Pesach even if they are purged by pouring boiling water on them ('iruy').  For they are like earthenware vessels, since their origin is from sand, and the Torah testified about earthenware vessels that they never [fully] emit [the absorbed ta'am]."[18]

 

     Coming from Rav Yechiel of Paris, this comment is astonishing. Recall that earlier we cited Rav Yechiel of Paris as saying, "Regarding a bone vessel we find no beli'a or issur."  We explained this to mean either that its physical attributes do not allow for beli'a or issur, or that in the absence of a source to the contrary, we may assume that any given substance does not absorb.  According to either of these two readings, we would have expected him to placed glass in the same category as bone.  However, in this passage, the Mordekhai cites Rav Yechiel as classifying glass as earthenware.

 

     Now, Rav Yechiel undoubtedly knew that earthen vessels, ceramics, are made of fired clay, not sand.  Yet he assumed that glass' originating from sand suffices to render it halakhically parallel to ceramics.  He most likely derived this parallel from a Gemara in Masekhet Shabbat (15), which deals with the halakhic status of glass with respect to tum'a.  On the level of Torah law, stone and glass utensils are not susceptible to tum'a.  Chazal, however, decreed that glass vessels can contract tum'a.  Rav Yochanan, citing Reish Lakish, explains the reason behind this enactment (15b): "Since they originate from sand, the Rabbis equated them to earthen vessels."[19]

 

     The Gemara thus appears to compare glassware with ceramics on the basis of the fact that both originate from the ground.  However, metal, which also originates from the ground, was not assigned the halakhic properties of earthenware.  We might therefore understand the similarity drawn between glassware and ceramics as based upon the processes of these utensils' production, rather than their origins.  Both glass and earthen utensils are produced via intense heat, which alters their crystalline structure, resulting in a fundamental change of their physical properties (though not necessarily with the same effect).

 

     Rav Yechiel apparently felt that this parallel would apply to the realm of kashering, as well, and we must therefore confer upon glass the halakhic status of cheres with respect to kashering.

 

b) A number of Rishonim felt that glass is categorized as metal with regard to beli'a[20], though no explanation is given for this classification.  Like with wood and stone, we can theorize that this ruling is perhaps based on experimentation (these Rishonim's determination of the physical properties of glass), or on their textual understanding that only earthenware is unkasherable.  Some Rishonim, invoke the aforementioned Gemara in Masekhet Shabbat, but, unlike Rabbenu Yechiel, ruled on the basis of the Gemara's conclusion that glass is closer to metal than to cheres.

 

c) Most Rishonim[21] felt that glass does not absorb any flavor at all.  Here, some Rishonim were more forthcoming in expressing their reasoning.  The Rashba[22] and Ra'avya[23], as well as Rabbeinu Tam (in O.Z. 33b s.v. konya, and in Ketubot 107b s.v. hani), attribute glass' inability to absorb on ta'am to its exceptionally smooth surface.[24]  The Ran (Pesachim, 9a in the Rif) cites this explanation and provides a source: "Since they [glass vessels] are smooth and hard, they absorb less than all other vessels… as it says in Avot De-Rabbi Natan: 'Glass vessels do not absorb and do not eject [ta'am]'."  Regarding glass, more so than with regard to other materials, it is clear that given the absence of clear textual guidance[25], the majority of the Rishonim based their pesak on the physical attributes of the material.

 

     [The Shulchan Arukh, Taz and Pri Chadash (ibid.) follow the majority view, that glass does not absorb.  The Rema (ibid.), based on the Terumat Ha-deshen[26], notes that common practice follows the stringent position of Rabbenu Yechiel.]

 

Conclusion

 

     Thus, in our survey of the Rishonim's opinions concerning "new" materials, we have seen examples of all four possible approaches outlined at the outset.  We have demonstrated the viability of all the possible approaches and halakhic possibilities (i.e. kasherable, unkasherable, and does not require kashering) and even added a fifth approach.

 

The approach LEAST employed is the de facto categorization of new materials as cheres due to halakhic doubt.  We saw only two examples of such a ruling: Rav Hai Gaon's view concerning stoneware, and Rav Yechiel of Paris' position concerning glass.  Rav Hai Gaon categorized stone as cheres, but it is unclear whether he did so due to its properties or because of its source.  No other Rishon follows his ruling, nor does the halakha accept this opinion.  As for Rav Yechiel of Paris, he categorized glass as cheres because it originates from sand, most likely in light of Chazal's comparison between glass and cheres in Shabbat 15.  He certainly did not arrive at this ruling based on a default cheres-like status of all utensils until explicitly stated otherwise.  This is evidenced by the fact that in his discussion of bone utensils, regarding which neither the Torah nor Chazal provide any instruction, Rav Yechiel himself writes that "we find no beli'a."

 

     The Rishonim who do not require kashering for a "new" material did so based on their observation of its physical properties (as we saw according to some views regarding glass, stone and bone), and/or based on mishnaic texts (other opinions regarding glass and stone).  While modern scientific testing methods are available to prove the physical properties of new materials, we obviously cannot hope for any source from the mishna regarding the status of much newer materials such as plastic.  Nevertheless, some poskim felt that plastic does not absorb or emit ta'am.[27]

 

     The most common direction among the Rishonim and poskim is to allow kashering these materials.  This is the accepted halakha regarding stoneware and bone utensils.  From a cursory survey of the poskim[28], this appears to be the most accepted position concerning plastics, as well.

 

     Nevertheless, the prevalent custom in America appears to be not to kasher plastic at all.  This practice likely stems from two main factors.  Firstly, affluence affords the population the luxury of "when in doubt, throw it out."  The second factor is the particularly strong influence of Rav Moshe Feinstein zt"l's opinion.  Since this teshuva has had such a profound impact upon halakhic protocol in the United States, I quote here a direct translation:

 

"Regarding the issue of rubber vessels, whether hag'ala is effective for them: Rubber, given that it is from trees [referring to natural rubber sap], haga'ala is effective.  And even if there is a [halakhic] doubt because some chemicals are [added], it is a doubt concerning a rabbinical issue which should be ruled leniently.  However, there is rubber which is not from trees, but rather from chemical compounds, which is a new substance that did not exist before the kadmonim [earlier rabbis].  One should not allow hag'ala [for utensils made from this substance." (Igrot Moshe, OC 2:92)

 

     Rav Moshe zt"l here clearly follows the second possibility we raised, namely, that we follow the rules that the halakha delineated for the given material's origin and components.

 

     But as we pointed out above, the only example of this approach is Rav Yechiel of Paris's ruling concerning glass.  We have noted the difficulties with this opinion and the fact that the majority of Rishonim disagree.  On the other hand, the Rema, as we mentioned, does observe the Ashkenazic practice not to kasher glass.

 

     Rav Moshe zt"l here makes a second assumption, as well, that a completely new material that had not existed before the "kadmonim" is considered unkasherable.  We have shown that such an approach has no precedent in the Rishonim.  Rav Shimon Eider, in his book "Hilkhot Pesach" (Chapter 13 fn. 5,10), records that in personal correspondence with Rav Moshe zt"l, Rav Moshe told him that he issued this pesak only with respect to chametz.  For kashrut throughout the year, however, one may kasher plastic utensils through hag'ala.  Unfortunately, this pesak was not adopted by the American mainstream.

 

Notes: 

1] Ta'am that remains permanently trapped in the material of the vessel is irrelevant. 

2] Some opinions do hold that "libun kal" acts like hag'ala, and other opinions maintain that hag'ala destroys ta'am in situ, but this issue lies beyond the scope of our discussion. 

3] Similarly, see Tosafot Chulin 8b s.v. she-libna. 

4] While there is some discussion among the Rishonim as to the exact definition of "etz ha-parur," according to all definitions it is used in a keli rishon. 

5] Rif (Pesachim, 8b in the Rif's pagenation), Riaz; Rambam, Hilkhot Chametz 5:24; Ramban, Rashba, Ritva, Rabbeinu David, Ran ad. loc.; Rosh, Pesachim 2:7; Mordekhai, Pesachim 553; Itur (II; Sha'ar Hekhsher Basar, p. 5 column 4). 

6] Pesachim 30b s.v. di-midayti. 

7] Two possible understandings of this limud come to mind. A) It operates as a sort of gezeira shava between the words, "shutaf" and "yishtof."  We must point out, however, that in the only instance of the word "yishtof" in the Torah, it does not refer to kashering a utensil.  The Torah says in Sefer Vayikra (15:12) concerning a zav (person who experiences a particular form of bodily impurity), "and an earthen vessel that is touched by a zav must be broken, but a wood vessel shall be rinsed in water ('yishatef')."  This pasuk refers SOLELY to the tum'a (impurity) caused by a zav, and not to the kashrut of the vessel.  Secondly, Rashi perhaps felt that one can indeed derive laws of kashrut from tum'a. In truth, the Itur and the Ran quoted in fn. 8 DO bring proof from halakhot pertaining to tum'a.  We do indeed find indications to this effect, but this lies beyond the scope of this discussion. 

8] These Rishonim include the BaHaG (Hilkhot Pesachim); the Rif (Pesachim 8b in the Rif); the Ran (ibid.); Rambam (Hilkhot Chametz 5:23-24); Itur (Hil. Hekhsher Basar); Rosh (Pesachim 2:7); Mordekhai (Pesachim 585), and others. 

9] Cited by the Tur O.C. 451. 

10] Rav Yitzchak ben Malki Tzedek of Simforet, quoted by the Ra'avya in Pesachim 464, Or Zarua, Avoda Zara 296-297, and Ran in Pesachim (8b in the Rif). 

11] Chapter 10. 

12] See the Ra'avya; then see notes 7 and 10.  The Ri Malki Tzedek seems to subscribe to the same parallel drawn by Rashi, the Ran and the Itur, but a fuller discussion is beyond the scope of this shiur. 

13] Other rishonim had a different version of the text, which reads, "break them" rather than "cleanse."  The Ra'avya held that "madichan" in this context means "purge." 

14] In truth, if we combine all the points raised in notes 7, 10 and 13, we might postulate a theory that kashrut of utensils is not based on absorbed or emitted ta'am, but rather, similar to tum'a, constitutes an objective gezeirat ha-Melekh.  Stone, which can never contract tum'a, would therefore not be subject to kashrut restrictions.  Such a theory, however, runs in opposition to the implication of poskim, Mishna and Gemara, all of which seem to recognize the physical reality of absorbed and emitted ta'am.

15] Rashi in responsa 76; Mikhtam, Pesachim 30b citing Rashi's Sefer Ora; Mordekhai, Pesachim ibid.; Meiri ibid.; Rema O.C. 451:5; Shulchan Arukh Ha-Rav ibid; Chayei Adam, 125; Shakh Y.D. 99:7; Taz 99:1. 

16] MaHaRi Weil, 193. 

17] Or Zarua (Avoda Zara 297) quotes Rav Yechiel and accepts his position even when dealing with "eyno ben yoma," meaning, a Torah prohibition. 

18] The Terumat Ha-deshen (132) rules similarly. 

19] A number of questions arise as to the applicability of this Gemara to the realm of kashrut. A) The gemara only addresses tum'a, not the kasherability of vessels. B) The fact that Chazal instituted this halakhic parity between glass and cheres actually proves that Torah law does NOT consider glass halakhically equivalent to cheres. C) Even after Chazal's enactment, glass is not ENTIRELY equivalent to cheres; for example, a glass utensil does not contract tum'a via its air space as earthenware utensils do (see Rashi, Bemidbar 19:15). 

20] The Ra'a (in Bedek Ha-bayit); Ritva; Shibolei Ha-leket; Rav Shmuel of Polias quoted in the Or Zarua. 

21] In addition to those following: Rabbeinu Tam; the Sefer HaEshkol. 

22] Responsa I 233. 

23] Pesachim 464 (p. 91). 

24] The assumption that a smooth surface ("she'ie") absorbs less is based on the gemara in Pesachim 74b that explains that the heart of an animal does not absorb prohibited blood because its surface is smooth. 

25] With the exception of the Ran, who combines the factor of physical attributes with a source from Avot De-Rabbi Natan. 

26] The Terumat Ha-deshen cites this position in the name of "R. Yoel," instead of "R. Yechiel." 

28] Rav Y.E. Hemkin zt"l as quoted by R. Shimon Eider in "Hilkhot Pesach," employing the same terminology used by the Rashba, Ra'avya and Rabbenu Tam for glass (see footnotes 23-25). 

29] Yesodei Yeshurun VI p. 170-174; Seridei Eish 2:160; Chelkat Yaakov 2:163; Tzitz Eliezer 4:6; Chazon Ovadya, Hilkhot Hag'ala 7.