The Mishnah in the end of Avodah Zarah (75b) instructs us that when we acquire utensils that have absorbed the taste of non-kosher food, the forbidden tastes must be purged from the utensils through hagalah, immersion in boiling water, or libun, scorching with fire. However, if we obtain utensils from a non-Jew, they require tevilat keilim, immersion in a mikvah, even if the utensils are new and have never been used.. The majority opinion among rishonim, supported by the Talmudic passage that quotes a Biblical source, contends that tevilat keilim is a Biblical imperative.

In general, whether an obligation has a Biblical or rabbinic source affects how we resolve doubts in halacha, as the operative principle is safeik d’oraita l’chumrah, safeik d’rabanan l’kula: we rule stringently in cases of Biblical law and leniently in cases of rabbinic law. Regarding tevilat keilim, the Talmud (ibid.) does not resolve the question of whether the utensil of a non-Jew that a Jew holds as collateral requires tevilah. Tosafot (s.v. ei mishum) rules that since the Talmud does not issue a definitive ruling on the matter, one should perform tevilah on such a utensil, albeit without a bracha. This is consistent with Tosafot's opinion (s.v. mayim) that tevilat keilim is a Biblical obligation. Shulchan Aruch (Yoreh Deah 120:9) codifies the opinion of Tosafot and also records (120:14) that a minor’s testimony that tevilat keilim was performed is inadmissible, for, as Beir Hagolah there explains, we do not accept a minor’s testimony regarding questions of Biblical law.

Materials
The Torah lists six types of metals that require purification when acquired from non-Jews: gold, silver, copper, iron, tin, and lead. Tiferet Yisrael (Yevakesh Da’at, Introduction to Taharot 44) quotes the Vilna Gaon as holding that the only metals that can contract ritual impurity are these six metals that are explicitly mentioned in the Torah. Tiferet Yisrael argues that other metals as well are subject to ritual impurity. Most poskim assume that whatever metals can contract ritual impurity require tevilat keilim.

The Talmud (ibid.) records in the name of Rav Ashi that glass utensils require tevilat keilim (presumably rabinically) because glass resembles metal in that it can be reconstituted after breaking. Tosafot (Shabbat 16b s.v. Rav Ashi) note an apparent contradiction in the position of Rav Ashi. While in Avodah Zarah he holds that glass utensils require tevilat keilim because of their resemblance to metal, in Shabbat he holds that glass resembles earthenware and therefore cannot contract ritual impurity. [Meiri (Avodah Zarah) records that this difficulty led to an erroneous practice of not reciting a bracha on the tevilah of glass.] Ritva (Shabbat 16b s.v. Rav Ashi) answers that the ambiguous status of glass led Rav Ashi to his seemingly contradictory opinions. Regarding tevilat keilim he adopts a stringent position that requires tevilah. However, regarding ritual impurity, since our general orientation is to minimize the amount of tumah in the world, Rav Ashi equates glass with earthenware.

The question of whether plastic utensils require tevilah hinges on whether Rav Ashi’s gezeirah applies only to glass or to any material than can be reconstituted after it breaks. While Minchat Yitzchak (3:76-78) requires tevilah for plastic, the consensus opinion among poskim distinguishes between glass and plastic (Chazon Ish, Rav Moshe Feinstein, and Rav Eliahu Henkin, quoted in Sefer Tevilat Keilim, Chapter 11, footnote 115). It is interesting to note that even though Rav Moshe Feinstein does not require tevilah for plastic, he writes that the rationale of Rav Ashi should apply to aluminum utensils, as aluminum can be reconstituted. Thus, even if one otherwise would assume like the Vilna Gaon quoted above that the Torah’s list of metals is exhaustive, aluminum should require tevilah miderabanan (Iggerot Moshe Y.D. 3:22).

Functions
The Talmud indicates that the only vessels that serve as kelei seudah, utensils used with a meal, are subject to tevilah. In explicating this principle, Shulchan Aruch (120:4) rules in accordance with a Hagaot Semak that tripods are exempt from tevilah because they do not come in direct contact with food, while grills require tevilah because food is roasted directly on them. Similarly, Shulchan Aruch quotes an opinion that a knife used exclusively for shechitah need not be toveiled. This assumes that only utensils that come in contact with food in an edible state require tevilah, and slaughtered meat is generally not consumed until it is cooked. Rama codifies the opinion of Issur V’heter (58:84-85) that an iron implement used to puncture holes in matzoh does not require tevilah. Rama does however quote an opinion that a knife used for shechitah should be toveiled and he recommends doing so without reciting a bracha.

The extent of Rama’s stringency is the subject of a dispute between Taz and Shach. Taz assumes that Rama’s recommendation to toveil the knife without a bracha presumes that tevilah may be required even for utensils that do not come in contact with edible food, and therefore applies to the matzoh hole punchers as well. Shach, though, distinguishes between the two, claiming that while in theory a shechitah knife could also be used for normal cutting of food, and therefore might require tevilah, the hole punchers have no conceivable use for food in an edible state. A practical difference between the opinions of Taz and Shach may be metal cookie cutters (assuming that people do not eat unbaked cookie dough). As cookie cutters are never employed with edible food, Shach would exempt them from tevilah totally, whereas Taz would suggest performing tevilah without a bracha. Sefer Tevilat Keilim (11:23) rules in accordance with Taz’s opinion.

Sefer Tevilat Keilim (1:4) rules that a serving utensil requires tevilah even if it is lined with paper or aluminum foil such that it never directly touches food. He does, however, record that R. Shlomo Zalman Auerbach exempted the old-style Israeli milk pitchers from tevilah since their primary usage involved placing a bag of milk inside them. Along these lines some poskim suggest that a blech does not require tevilah because food is not normally placed directly on it. (If the food is not in a separate utensil it is generally at least wrapped in aluminum foil. This might also justify not subjecting refrigerators and refrigerator shelves as well as oven ranges to tevilah. See Sefer Tevilat Keilim 1:10, 11:4). Rabbi Hershel Schachter has noted that a blech should be analogous to a cookie platter that is always covered with a protective layer of paper, which, according to Darchei Teshuvah requires tevilah.

Disposable Utensils
The technology of the twentieth century presented poskim with new questions regarding applications of tevilat keilim. Do disposable utensils, such as aluminum foil pans, require tevilah? Rambam (Hilchot Keilim 5:7) rules that utensils that are used and then disposed of cannot contract ritual impurity. If the aforementioned equation between ritual impurity and tevilat keilim stands, disposable utensils should be exempt from tevilah. This is the conclusion of Shu”t Minchat Yitzchak (5:32:1) and Shu”t Chelkat Ya’akov (4:115).

R. Moshe Feinstein (Iggerot Moshe Y.D. 3:23), based on an inference in a Rambam (Hilchot Keilim 2:1), appears to take a more nuanced position. If the utensil in question will generally not withstand more than two or three uses, then even if a person uses it repeatedly, it does not require tevilah. If, however, the utensil is sturdy enough to be used repeatedly, but people tend to dispose of it after a single use because of its cost, tevilah must be performed.

A similar question arises with food that comes in a glass jar or bottle. The consensus of poskim is that one need not pour out the contents of the vessel and perform tevilah; one may remove the contents in normal fashion as he sees fit. Shu”t Chelkat Yaa’kov (2:57) reasons that the buyer never intended to acquire the jar, as doing so would necessitate violating the requirement of tevilat keilim. R. Moshe Feinstein (Iggerot Moshe Y.D. 2:40 and R. Shlomo Zalman Auerbach (quoted in Sefer Tevilat Keilim Chapter 4 footnote 14) suggest that when one purchases food in a glass utensil the utensil’s identity is subsumed under that of the food and therefore it does not need tevilah. R. Feinstein even suggests that one may reuse the utensil after removing its initial contents without performing tevilah. The Jew’s decision to reuse the utensil is what makes it a utensil from the perspective of halacha, and halacha therefore views it as utensil fashioned by a Jew. (See Sefer Tevilat Keilim 4:13 for a presentation of those who dispute this novel ruling.

Electrical Appliances
Yad Efrayim (gloss to Yoreh Deah 120:5) quotes Shu”t Shev Ya’akov 31 (in our printing it is misattributed to Shu”t Shevut Ya’akov) who posits that a heavy utensil that is permanently attached to the ground does not require tevilah, as it cannot contract ritual impurity. Shu”t Minchat Yitzchak (4:114:4) rejects this leniency outright, dismissing this application of the equation to ritual impurity. Shu”t Chelkat Ya’akov (1:116) assumes that an electrical appliance that only works when plugged in to a current is the halachic equivalent of a utensil permanently attached to the ground. He writes regarding this that if one is concerned that dipping an electrical appliance into water will ruin the appliance he may rely on the Shev Ya’akov and not perform tevilah. Shu”t Shevet Halevi (2:57:3) writes that even if one were to assume like the Shev Ya’akov, an electrical appliance does not have the status of a utensil attached to the ground.

Most poskim assume that electrical appliances do require tevilah (see Sefer Tevilat Keilim Chapter 11 footnote 46). Experience has shown that under most circumstances immersing electrical appliances in water does not harm them so long as they are left out to dry for a week prior to usage. R. Moshe Feinstein (Iggerot Moshe Y.D. 1:57-58) writes regarding the old-fashioned electric urns that the part with the wiring (the bottom of the urn) need not be immersed. Since water is not placed it that section it is not considered part of the vessel.