The end of the article answers the question: “Why are we discussing this topic the week of Parshas Matos?”
Question #1: Warming bottles
“On Shabbos, may I pour hot water onto a baby bottle containing milk or formula?”
Question #2: Sinks
“May I use my sink for both milchig and fleishig?”
Question #3: Iruy into liquids
“Does iruy cook when it falls into a liquid?”
“Why are we discussing this topic the week of Parshas Matos?”
Although our opening questions may appear unconnected, they all relate to a halachic topic called iruy kli rishon. This term refers to the halachic status of food or vessels that were heated by having hot liquid poured on them. For example, preparing a cup of tea by pouring hot water from a kettle or urn into a cup containing a tea bag is a typical case of cooking by use of iruy. Pouring hot chicken soup directly from the pot into a milchig bowl is another situation of iruy kli rishon. The word iruy means pouring,and the term iruy kli rishon means that the liquid was poured from a pot or pan that was heated directly by the heat of a fire. This article will discuss the background and the basic rules of iruy kli rishon and some halachic ramifications. As usual, our purpose is not to paskin everyone’s halachic queries. That is the role of each individual’s rav or posek.
Iruy kli rishon affects many common situations, including, for example:
The status of milchig and fleishig items in your kitchen.
How one may warm food on Shabbos.
Whether a food or utensil became non-kosher.
How to kasher utensils that became non-kosher.
To make this presentation clearer, let us clarify four relevant terms:
Yad soledes bo
Whenever in this article we mention something is hot, it means that it is at least yad soledes bo, meaning that it is hot enough that a person pulls his hand back, instinctively, when he touches it. There is much dispute among halachic authorities how we measure this in degrees, which is a subtopic that we will leave for a different time.
At times, we will refer to something being cooked or absorbed kdei kelipah. For the purposes of this article, this means that, at the point of contact of the heat, some cooking or flavor absorption transpires, but does not extend further.
A kli rishon is a pot, pan or other vessel that was heated directly from a source of heat, such as on a stove, inside an oven, or any other way.
A kli sheini is the platter or bowl into which food is poured from a kli rishon.
An anecdote from the Gemara will clarify the status of a kli sheini.
Although most forms of hot bathing are prohibited on Shabbos, it is permitted to bathe in hot natural springs, such as those found in Iceland, Teverya, and Hot Springs, Arkansas. The Gemara (Shabbos 40b) records that Rabbi Yehudah Hanasi, also known as Rebbe, was bathing in the hotsprings of Teverya on Shabbos and was being waited on by his disciple, Rav Yitzchak bar Avdimi. Rav Yitzchak bar Avdimi had a flask of oil for Rebbe to use for anointing after he finished bathing, and Rav Yitzchak wanted to warm the flask so that the oil would be more comfortable. Rav Yitzchak asked Rebbe whether he could warm the oil in the hot spring; Rebbe replied that he may not. Then Rebbe suggested a different approach: Rav Yitzchak bar Avdimi could fill a container with hot spring water, then place the container of oil inside the larger container of hot water.
Tosafos (ad loc.) asks why the latter procedure is permitted, whereas placing the flask of oil directly in the hot spring is prohibited. In both instances, the oil is heated by water from a natural hot spring. Tosafos answers that when the vessel itself is on the fire or inside the oven, the heat of the liquid is maintained by the hot walls of the vessel, and that is why bishul occurs. However, when the container itself was never directly warmed – what we call a kli sheini – the walls of the vessel diminish the heat. As a result, the oil will not cook from the heat of the water. In other words, cooking in a vessel requires not only sufficient heat, but that the walls of the pot or vessel maintain the heat. Therefore, cooking can occur in a kli rishon but not in a kli sheini.
Here is another distinction between kli rishon and kli sheini: The Mishnah (Shabbos 42a) teaches that if a pot was removed from the fire on Shabbos, one may not add spices, because this constitutes bishul. However, one may add spices to a platter containing food that was poured out of the original pot. The second case is a kli sheini, meaning that the platter itself was never on the fire. Again, the indication is that cooking requires the walls themselves to have been heated.
Iruy kli rishon
We see that whereas a kli rishon is capable of cooking, a kli sheini is not. What about pouring from a kli rishon, which is an in-between level? The hot stream coming from iruy kli rishon has no vessel walls to maintain its heat – but it also has no walls cooling down the heated product. Do the heated walls of the kli rishon cause the cooking, in which case iruy kli rishon would not be considered cooking, or is it the cooling kli sheini’s walls that prevents cooking from transpiring, in which case iruy kli rishon would be considered cooking? This question is debated extensively by the rishonim and early poskim.
Among the main players who weigh in on the discussion are two of Rashi’s illustrious grandsons, the Rashbam and Rabbeinu Tam (Tosafos, Zevachim 95b). The Rashbam maintained that iruy does not cook, just as a kli sheini does not. His younger brother, Rabbeinu Tam, disputed this, and contended that iruy kli rishon can cook, at least to a certain extent.
Among the Baalei Tosafos, we find a further dispute regarding whether Rabbeinu Tam held that iruy kli rishon cooks and causes absorption of flavor through the entire product or only kdei kelipah. We will be assuming the second of these approaches, which is held by the majority of authorities.
The background behind this discussion takes us to a different passage of Gemara.
Within the context of a hot substance falling on a cold one, or vice versa, we find a dispute in the Gemara (Pesachim 75b-76a) between the great amora’im, Rav and Shmuel, as to who “wins” – the one on top or the one on the bottom. As explained by Rashi, the Gemara teaches:
If hot food fell into hot food, such as hot meat fell into hot milk, or when one item was kosher and the other not, everyone agrees that the resultant mixture is non-kosher. The flavors of the two products became mixed because of the heat, and the result is no longer kosher.
If both food items were cold, and one can separate the two products, that which was originally permitted remains so.
The dispute between Rav and Shmuel is when one food is hot and the other cold. Rav contends that when the upper one is hot, the flavor of one food mixes into the other, rendering them both non-kosher; however, when the lower one is hot and the upper is cold, the flavors do not mix. Therefore, if the foods did not become mixed, the kosher one remains kosher. This is referred to as ila’ah gavar, literally, the upper one is stronger.
Shmuel rules that when the lower item is hot, we rule that the flavors mix, and everything becomes non-kosher. However, when only the upper one is hot, it cools off when it mixes into the lower one. This is referred to as tata’ah gavar, meaning, “the lower one is stronger.” The Gemara concludes that, according to Shmuel, when a hot substance falls into a cold substance, there is a mixing of flavors on a thin layer of the food, which is called kdei kelipah. Therefore, a thin layer is sliced off the food at the point of contact, since that layer absorbed non-kosher flavor. The rest of the food remains kosher. This ruling will be a major factor in our discussion.
Rashi notes that, although in matters of kashrus and other laws called issur veheter we usually rule according to Rav and against Shmuel, in this particular debate we rule according to Shmuel. The reason is because the Gemara notes that two different beraisos, teachings from the tanna’im, ruled like Shmuel. Thus, most of the rest of our discussions assume that tata’ah gavar.
Let us now return to the dispute between Rabbeinu Tam and his older brother, the Rashbam, concerning whether iruy is considered to have cooked something. Some authorities, following the approach of Rabbeinu Tam, contend that just as Shmuel ruled that when one pours a hot food onto a cold one, we assume that kdei kelipah became absorbed, when pouring hot water onto a cold food (such as a teabag) on Shabbos; we must assume that a kdei kelipah becomes cooked. Thus, it is forbidden, according to Rabbeinu Tam, to pour hot water onto cold, uncooked food on Shabbos. The consensus of halachic authority is to accept this ruling and to prohibit pouring hot water from a kli rishon onto cold, uncooked food on Shabbos.
Above, we noted that when a hot substance falls into something cold, the hot substance is absorbed into the cold one to a depth of a thin layer of food. One question to resolve is whether this ruling is min haTorah oronly miderabbanan. A prominent early acharon, the Magen Avraham (467:33), contends that this ruling (that a layer of the cold food becomes prohibited) is only a chumra be’alma, meaning that min haTorah no absorption takes place, but that Chazal prohibited kdei kelipah.
Despite the Magen Avraham’s position, it is evident from many rishonim that they understood that kdei kelipah is prohibited min haTorah.
At this point, let us examine our opening question:
“On Shabbos, may I pour hot water onto a baby bottle full of milk?”
We have learned that when pouring hot water from a kli rishon, the outer surface of the food may become cooked.
However, let us think for a moment about our question. Iruy potentially can cook only the outer surface, which, in this case, is the bottle itself. Observation tells us that, even assuming that vessels can become “cooked,” bottles do not become cooked by pouring boiling water on them, since they are too hard to become changed, either physically or chemically, by this amount of heat. Furthermore, the milk inside the bottle is not in the surface kdei kelipah, and, therefore, although the milk inside the bottle will become warm or even hot, it is not being cooked. Consequently, it is permitted to warm baby’s bottle on Shabbos by pouring hot water onto the outside of the bottle.
Iruy into liquids
Let us move on to the next of our opening questions: “Does iruy cook when it falls into a liquid?”
We learned that iruy kli rishon causes a small degree of absorption, and, according to Rabbeinu Tam, it also cooks. At this point, I raise a question: Perhaps this is true only when the hot water is poured onto a solid food or a vessel? Could one argue that no cooking takes place when one pours from a kli rishon into a bowl of liquid?
Why should there be a difference between a solid and a liquid? When one pours directly into a liquid, what one pours immediately disperses into the liquid into which it falls. Perhaps all the heat that would cause absorption kdei kelipah dissipates throughout the liquid and, consequently, no cooking takes place. Indeed, we find rishonim who espouse this position (Tosafos, Pesachim 40b s.v. Ha’ilpeis). Nevertheless, this is not a universally held position, and the consensus of later authorities is that we do not differentiate between liquids and solids: In all instances, we conclude that iruy kli rishon does cause some cooking (Pri Megadim, Mishbetzos Zahav, Yoreh Deah 68:9 s.v. Hadin Hashelishi).
At this point, we can explain a different halachic question: A hot potato is on my plate, which is a kli sheini since it was not on the fire. May I place uncooked seasoning onto the potato on Shabbos?
We learned above that I am permitted to put uncooked spices into a kli sheini. It would appear, then, that I am permitted to add raw spices to my hot potato, which is sitting in a kli sheini. Indeed, we find major authorities who seem to agree that this is considered a case of a kli sheini (see, for example, Rema, Yoreh Deah 94:7).
Nevertheless, many authorities disagree with this conclusion (Maharshal, Yam shel Shelomoh, Chullin 8:71). They note the following: Tosafos explained that the difference between a kli rishon and a kli sheini is that the cooler walls of the kli sheini are reducing the heat; this prevents cooking from taking place.
However, a hot potato on a plate is not being cooled down by the plate. Since it touches the plate on only a minimal amount of its area, perhaps the potato itself retains the halachic status of a kli rishon. This is referred to as davar gush, a solid food not having the halachic advantages of a kli sheini. Most of the commentaries on the Shulchan Aruch rule that, generally, we should be concerned about both approaches: that of the Rema,who considers this a kli sheini; and that of the Maharshal, who considers this a kli rishon. As a practical matter, this means that one usually treats a davar gush not as a kli sheini but as a kli rishon (Shach, Yoreh Deah 105:8; Taz, Yoreh Deah105:4; Magen Avrohom, Orach Chayim 318:45).
At this point, let us examine another of our opening questions:
“May I use my sink for both milchig and fleishig?”
The question here is as follows: A sink does not have its own heating element. As such, it is never a kli rishon, but qualifies either as an iruy situation or as a kli sheini. We learned above that iruy can cause cooking and absorption, at least kdei kelipah. For these reasons, many authorities contend that someone who has only one sink in the kitchen should treat it as treif and use either dishpans or something similar and avoid putting dishes directly onto the sink surface (see, for example, Shu”t Minchas Yitzchok 2:100). On the other hand, based on an extensive analysis of the halachic sources, one major authority concludes that using a sink for both milchig and fleishig does not meet the characteristics of iruy kli rishon and is permitted (Shu”t Igros Moshe, Yoreh Deah 1:42). I refer our readers to their own halachic authority for a practical ruling.
At this point, let us examine the last of our opening questions:
Why are we discussing this topic the week of Parshas Matos?
After the Bnei Yisroel’s miraculous victory over the nation of Midyan, they were commanded regarding the spoils that they had now acquired: Concerning the gold and the silver; the copper, the iron, the tin and the lead: any item that was used in fire needs to be placed in fire to become pure – yet, it must also be purified in mikveh water. And that which was not used in fire must pass through water (Bamidbar 31:22-23). Here the Torah introduces the concept of kashering vessels that have absorbed non-kosher foods. In this instance, the vessels of Midyan had been used for non-kosher; could the Jews use them? The answer is that they could kasher each item in a way that expunges the non-kosher absorption, and the vessel would become kosher. As Rashi explains the posuk, any item that was used directly in fire needs to be placed directly in fire to become kosher. And that which was not used in fire directly, but was used to cook with hot water on top of the fire must pass through water that was heated directly by a fire, to kasher it.
Does something that absorbed non-kosher via iruy require kashering? According to the conclusion above, it does – since we assume that iruy kli rishon causes some absorption into the walls of the vessel. But it can be kashered through iruy kli rishon (Tosafos, Shabbos 42b s.v. Aval).
We now have some understanding of a complicated halachic issue with all sorts of ramifications. It provides an appreciation how much one’s rav or posek must keep in mind every time he answers one of our questions. Certainly, this is a time to value his scholarship and his making himself available when we need him.