We will now discuss how to do two common methods of kashering for Pesach, hagalah and irui.
Hagalah
Hagalah kashers a utensil by immersing it into boiling water, purging it of its chametz or non-kosher absorptions.
Hagalah involves five steps.
Step 1 — Preparing the Utensil for Hagalah
Step 2 — Having a Hagalah Pot
Step 3 — Heating the Hagalah Water
Step 4 — Immersing the Utensil
Step 5 — Rinsing the Utensil After Hagalah
Step 1 — Preparing the Utensil for Hagalah
Scrubbing: Hagalah removes non-kosher absorptions. It does not, however, remove actual non-kosher substance that has adhered to the utensil. A utensil must therefore be scrubbed thoroughly to remove any actual food substance before immersing it in the hagalah water.115 Rust must also be scrubbed down, out of concern for small pieces of food residue that are underneath. Rust that is a mere discoloring, though, is not considered a problem.116 Furthermore, handles or other parts that can be removed from the utensil should be detached,117 and the spot where they were attached to the vessel — as well as the handles or other parts themselves — should be cleaned well.
Crevices in a utensil can be problematic, since they may contain chametz residue, yet they cannot be thoroughly scrubbed. A common example would be the underside of a pot’s lip. Before kashering the whole utensil, these areas must be purged via the process of libbun kal118 — by applying heat to the area of the crevice (albeit, a lower degree of heat than libbun chamor), any residue will become burnt up and will no longer be considered chametz. Once these areas have been rid of their chametz residue, hagalah (or libbun kal) is done to the utensil as usual.
If libbun kal cannot be done to the utensil, for example it will ruin it, the utensil should not be used on Pesach. Rather, it should be put away during Pesach.
Waiting Twenty-Four Hours Since Last Use: Hagalah removes non-kosher or chametz absorptions from a utensil. But unlike libbun which incinerates these absorptions (discussed in Section I above), hagalah merely extracts these absorptions from within the utensil — they remain, afterwards, in the hagalah water. Thus, a question arises: why do these absorptions not become immediately reabsorbed into the utensil’s walls?
The Rishonim119 give several answers to this question. Some explain that hagalah should be done with an amount of water that is sixty times as much as the size of the utensil being kashered. Thus, any chametz flavor that leaves the kashered utensil will immediately become batel b’shishim (nullified in a sixty-to-one ratio of permitted substance to forbidden) before it can reenter the utensil.
Another answer is (as discussed in Section II) because, if an absorption is eino ben yomo, it no longer imparts positive flavor; thus, bedieved it remains permitted. Therefore, even if these absorptions enter the original utensil again, they are no longer problematic.
The minhag120 is to only perform hagalah on a utensil that has not been used within the previous twenty-four hour period. Since its absorptions are not fresh, they will not render a utensil non-kosher (nosein ta’am lifgam), and not rely on there being sixty times as much water as the size of the utensil. This is because we are concerned that one may slightly miscalculate the size of the utensil, and immerse it in water that is less than a sixty-to-one ratio.121
Step 2 — Having a Hagalah Pot
Ideally, before beginning to boil the hagalah water, one should make sure that the large pot being used for this purpose is itself kosher for Pesach. If a large pot that has been kashered for Pesach122 is not available, one may use a pot that has been used for chametz, provided that it has not been used in the past twenty-four hours.123
Step 3 — Heating the Hagalah Water
Under normal circumstances, hagalah should be done in water, and not in other liquids.124 If the water is brought to a boil exclusively by solar or geothermal energy, it is unacceptable for hagalah, no matter the temperature.125 However, if water was heated in these ways and then was subsequently brought to a boil using conventional means (such as fire or electricity), it remains acceptable.126
Hagalah should not be done unless the water is bubbling vigorously.127
Step 4 — Immersing the Utensil
The utensil is submerged in the boiling water, which remains over the fire throughout the hagalah process.128 Immersing the utensil, which is an object that is much cooler than the boiling water, will inevitably cause the water to cool down somewhat.129 If the water cools to the degree that it stops bubbling, the utensil should be left under water for several seconds after the bubbling resumes.130
The entire utensil, including the handles,131 must enter the hagalah water. However, when kashering under the usual guidelines discussed above — that the utensil is eino ben yomo — the entire utensil need not be submerged at once (unlike tevilah). One part of the utensil may be submerged and taken out of the water, and when the bubbling resumes, the rest of the utensil may then be inserted.132
Several utensils may be submerged and kashered simultaneously, providing that one utensil is not touching another while underwater. The only parts of a utensil that are effectively purged are those with which the hagalah water comes into direct contact.133
Common practice is that the utensils are immersed and removed from the boiling water with tongs, or while wearing large rubber heat-resistant safety gloves that cover the hands and forearms. Care must be taken that the utensil being kashered is held in more than one place while underwater, to allow the boiling water to come into direct contact with every area. Alternatively, the utensils may be submerged in a metal mesh basket that allows the hagalah water to reach inside the basket.
Step 5 — Rinsing the Utensil After Hagalah
The minhag is to immediately rinse the kashered utensil with cold water after removing it from the hagalah water.134 However, if this was not done, the utensil remains permitted.135
Irui
As discussed above in Section I, irui (pouring boiling water) is essentially a type of hagalah, for it likewise entails using boiling hot water to purge an object of its absorptions. Pouring hot water onto the utensil or surface, however, is less effective than “real” hagalah — that is, immersing a utensil into a pot which is still boiling on the fire. Thus, if a utensil had absorbed a chametz or non-kosher liquid while directly on the fire, irui will be ineffective. However, an item or surface that absorbed chametz or non-kosher taste not by direct contact with the heat source but rather via spills — that is, from hot liquids being poured upon them — need only be kashered via a similar method of pouring. This is because of the general principle of kebolo kach polto explained above. Irui is therefore an effective method of kashering utensils and surfaces upon which hot chametz or non-kosher liquid was poured.
Irui is performed by heating up water to a strong boil. The pot filled with boiling water is then poured directly on the item or surface that one is kashering.
The item or surface that is being kashered must be dry before the irui water is poured upon it. Otherwise, the cold water on the surface will lower the temperature of the water being poured on it, which reduces the hot water’s ability to purge the absorptions from the item or surface.136
The flow of water from the hot pot to the item or surface being kashered must be uninterrupted.137 A flow that is uninterrupted has a greater ability to imbue (or extract) taste than that which is interrupted. Since the non-kosher substances may have been poured without interruption, the principle of kebolo kach polto requires that the irui kashering process must likewise be uninterrupted.
Irui only kashers the spot where the water hits directly when poured from the pot. It does not kasher the other areas on the surface where the water continues to flow.138
The water must be poured directly from the pot in which it boiled. Transferring the water to a second utensil before pouring it on the surface somewhat cools it, making it no longer effective to kasher the surface that absorbed hot chametz or non-kosher.139
When irui is performed in conjunction with an even melubenes, one heats the stone to a temperature hotter than the hagalah water (i.e., hotter than 212 degrees Fahrenheit).140 One places the heated stone on the dry surface, and pours the hot water onto it. One moves the stone (with tongs) all around the surface so that it will have its effect on the entire surface.141
Warning: Be very careful when using an even melubenes, to avoid creating a fire-hazard.
115 See Shulchan Aruch 451:3, Mishnah Berurah note 42.
116 Shulchan Aruch 451:3, with Mishnah Berurah note 22.
117 Technically, if the handles or other pieces are firmly attached to the extent that it is not feasible for residue to seep in, they need not be removed. However, it is sometimes difficult to ascertain whether or not it is feasible that food residue may have seeped in. Therefore, as a general rule, if the handles or other pieces can be removed and cleaned, one should do so. This is especially true since, if they can be unscrewed, there is a greater likelihood for food residue to seep in.
117In the event that the handles or other pieces cannot be removed, one has to determine whether or not it is feasible for crumbs or food residue to have seeped in. In the event that chametz did seep in, one may not kasher the utensil unless libun kal is done first.
118 Shulchan Aruch 451:13 with Mishnah Berurah note 76.
119 See Tosafos Chullin 108b ד”ה שנפל.
120 Rema 452:2.
121 Mishnah Berurah 452:20. Note, in a scenario where several utensils are being kashered at one time in the same water, one would need sixty times the volume of all of the utensils put together, unless they are eino ben yomo.
122 Large pots, which cannot be immersed in another pot, may be kashered by filling them with water that comes to a heavy boil. A burning stone is then placed in the water, causing the water to boil over and kasher the rim and outsides as well (Shulchan Aruch 452:6).
123 Mishnah Berurah 452:13.
124 Rema 452:5.
125 Shulchan Aruch 452:5, Haggadah Shel Pesach of R’ Yosef Shalom Elyashiv, p. 11.
126 Haggadah Shel Pesach of R’ Yosef Shalom Elyashiv, ibid.
127 Shulchan Aruch 452:1.
128 Rema 452:1.
129 Mishnah Berurah 452:8.
130 See Mishnah Berurah 452:8.
131 Shulchan Aruch 451:12, Mishnah Berurah note 70.
132 Bei’ur Halachah 452:1 ד”ה צריך.
133 Shulchan Aruch 452:3, Mishnah Berurah note 22.
134 Shulchan Aruch 452:7.
135 Mishnah Berurah ibid. note 34.
136 Mishnah Berurah 452:20.
137 Ibid.
138 Siddur Pesach Kehilchoso I, 2:3.
139 Mishnah Berurah 452:20.
140 See Hagalas Keilim, Chapter 11, footnote 30 [p. 263].
141 Technically, either a stone or metal may be used for this purpose, but metal cools more quickly when water is poured on it than stone does, so for extended use, a stone may be more practical.
There is an advantage to using a larger stone rather than a smaller stone (based on Issur V’hetter 58:71, cited in Be’er Hagolah to Rema, Yoreh De’ah 135:15).
In the ordinary kitchen, the only practical instances of using an even melubenes would be when kashering a countertop or a sink. In these situations, the requirement for the even melubenes is due to the concerns that the surface might have had hot solid chametz placed on it (davar gush), which might have the status of a kli rishon. For these concerns, the water used for irui may be poured from a kli rishon or from a kli sheini. Furthermore, it makes no difference whether one first places down the stone and then pours the hot water over it, or vice versa (see Libun Hilchesa, Hagalas Keilim pp. 239-249; Hagalas Keilim 11:18). For a flat surface, the heated stone must be moved all around the area being kashered; for a receptacle filled with hot water (e.g., a sink filled with water), some maintain that it is sufficient to simply place the stone into the hot water without moving it around (Hagalas Keilim Chapter 11, footnote 39; see, however, Libun Hilchesa ibid.).
When kashering a countertop with an even melubenes, some suggest using an iron instead of a stone.