Taste transfers in complex ways according to halakha. When a forbidden food gets mixed up directly with a permissible one – they are blended together, or cooked together so they all become one mass, there is no question that the forbidden food is present, and that the mixture will be forbidden unless the forbidden food is less than 1/60th of the whole. But what about when it is not clear if the forbidden food transferred its taste into the mixture? Say a treif piece of meat falls into my chicken soup and then I remove it – under what circumstances would I say that the taste of this treif meat transferred into my chicken soup?
Rishonim focus primarily on two criteria that may be required to transfer taste – the heat and the vessel. Both of these principles are derived from Talmudic discussions regarding cooking on Shabbat. The Talmud (Shabbat 40b) states that cooking of liquids only occurs when the liquid reaches the temperature of yad soledet bo, when the hand would draw back from touching it. There is debate as to how hot this is, with Rav Moshe setting the range between 110-160 degrees Fahrenheit, and Shmirat Shabbat KiHilkhata quoting Rav Shlomo Zalman Aurbach who states that it is not less than 113 degrees Fahrenheit. Now, while the Gemara only states that this is how to define that a liquid has been cooked, we assume that it is also the temperature necessary for a liquid to cook something else. Thus, if I put a raw vegetable or instant oatmeal or the like in liquid less than 110 or 113 degrees, there would be no problem of cooking on Shabbat.
As far as the vessel itself is concerned, halakha defines the vessel that was on the fire – the pot, the frying pan, etc. – as a keli rishon – the first vessel. After that, every next vessel the food is poured into is defined as the next ordinal number – the pot that cooked the soup is the first vessel, the soup bowl is the second vessel (keli sheini), and so on. Now, for Shabbat, the general rule is that cooking only occurs in a keli rishon (see Shabbat 42b). Ramban, on the basis of the Yerushalmi, goes further and states that the Biblical melakha of cooking only occurs in a keli rishon while it is still on the fire (it would still be Rabbinically forbidden to cook in such a vessel once it is removed from the fire). We rule against Ramban, and rule that it is a melakha to cook in a keli rishon even if it is off the fire.
Thus, if I put a raw vegetable in the pot that my chicken soup was cooking in, I would have done the melakha of cooking only if the soup was yad soledet bo and the pot was the same one that the soup was cooked in, even if now it is removed from the fire. It would not be cooking if I put the vegetable in my soup bowl, even if the soup was still very hot and yad soledet bo.
The reason heat is necessary is obvious – things don’t cook without heat. But why does it matter if something is put in a kli rishon or a kli sheni? Tosafot (Shabbat 40b, s.v. u’Shma) asks this question and states that a kli rishon, because it had been directly on the fire, retains the heat of what is inside it better than a kli sheni does. This is obviously correct – my soup stays hotter in the soup pot, even off the fire, than it does in my soup bowl. Most things, even if put on the fire or in a hot liquid, need time to go from being raw to being cooked. Thus, states Tosafot, for halakhic cooking to occur, one must use a vessel that normally can create the environment to cook something over a period of time, and thus a kli rishon is needed.
To al large degree, Tosafot’s approach is based on an assessment of the real-world issue of whether something will cook in a keli sheni. An alternative, more formalistic, approach would be to borrow from Ramban’s position that true cooking is over a fire. Thus, even when we rule that cooking can occur off a fire, we would still insist that it take place in the context of, or with a connection to, a fire. Thus, if one puts oatmeal in a kli rishon, like a pot that has boiling water in it, even though it is off the fire it is considered cooking, because it is as if it was cooked on the fire. Halakha can consider this to be a formally defined act of cooking because it occurred in a vessel heated on a fire, so it exists in the same ambit of the act of classic cooking, which occurs directly on the fire. If, however, if one puts oatmeal in a kli sheni, for example, in a bowl that one poured hot water from the kettle into, then although it may be cook in real-world terms, she would not have done a halakhic, formally-defined act of cooking, because fire was not involved.
The two ways of understanding the need for keli rishon explains a number of debates. First, there is the question whether anything can cook in a keli sheni. The Gemara (Shabbat 42b) raises this issue without coming to a clear conclusion. The Yeraim is very concerned with this possibility, and rules that we must be consider any food to possibly be something that can cook easily – kalei ha’bishul – and therefore if the water is yad soledet bo, we should not cook on Shabbat in that vessel no matter what type of vessel it is. If it is a concern of whether the object will really become cooked or not, there is no difference between a keli sheni and a keli shlishi or ri’vi’ee. The only issue is the heat of the water.
We do not follow the Yeraim li’halakha. We rule (Orah Hayim 318:9) that it is not considered cooking on Shabbat unless one uses a kli rishon. Nevertheless, the Rema (ad. loc.) and the Mechaber (318:5) mention that it is appropriate to be careful about 2 things that might cook more easily than others – salt (not an issue today when our salt is processed and already cooked) and bread, and that li’chatchila one should not place these in a keli sheni if the water is yad soledet bo. Allowing for these exceptional cases, although initially only as chumrot, opened the door for Yeraim-like concerns. Thus the Magen Avraham, and following him the Mishne Brurah, are concerned, like the Yeraim, that almost everything may be kali ha’bishul and able to cook in a keli sheni. Unlike Yeraim, they are not generally concerned with a keli shlishi. If, however, we see that something does cook in a keli shlishi, that may also be considered cooking. This question -whether a keli shlishi could ever cook – is central to the debate around using tea bags on Shabbat, and Arukh HaShulkhan, for one, forbids using them on the basis that they always cook when the water is hot, regardless of the keli.
What is at the root of the debate around the keli sheni and keli shlishi is the question of why a keli rishon is important. If, as Tosafot says, it is because of the reality of whether the heat will be retained long enough to effect cooking, then it is possible that there are some foods that do not need a long time to cook – kalei ha’bishul – and thus could cook in a keli sheni. That is, if one is real-world oriented, the halakhic definition will change based on different circumstances. On the other hand, if the need for a keli rishon is to consider the process of cooking as if it took place on the fire, or was connected to the fire, then this formal definition – e.g., “cooking is the act of placing food on a fire, or in a vessel that was heated on a fire, to transform or prepare the food or to make it edible.” – does not change even if the food does get cooked in real-world terms. The hardest position to understand is the compromise one that we adopt, that states that cooking may occur in a keli sheni but does not occur in a keli shlishi. This may be a claim about the real-world ability for a keli shlishi to effect a change in the food (hence the exception that some make to this rule when it comes to tea bags), or it may be that this approach also adopts a formalist definition, although a broader one, “cooking is the act of placing food on a fire, or in a vessel that was heated on a fire, or in a vessel that is one degree removed from the original one, to transform etc.” However, it is hard to understand why, were we to adopt a formal definition, we would adopt this one.
This issue – whether the definition of cooking is a formal one or a real-world one – may also be at the center of the debate around the status of iruy, pouring from a keli rishon. Rabbenu Tam is of the opinion that iruy is like a keli rishon, and it effects cooking on the food that the water is being poured on. Rashbam, on the other hand, is of the opinion that it is like a keli sheni and does not effect cooking on the poured-on food. (See Tosafot, Zevachim 95b, s.v. Eera). If one adopts a formal definition, then the case of pouring from a keli rishon should qualify as cooking, since that process still connects to the vessel that was on the fire. This is further evidenced in the qualification, introduced by Tosafot, that this applies only if it is lo nifsak ha’kiluach, if the stream hitting the food is connected to the vessel at the other end. Once the stream is disconnected from the vessel, the process no longer relates to the vessel and no longer relates to the fire. This would be the position of Rabbenu Tam. On the other hand, if it is a real-world concern about the retention of heat, once one is pouring the liquid out of the vessel, and in such a short-duration process – the ability of the vessel’s walls to retain heat should be irrelevant. This would be the position of Rashbam. [It should be noted that it is possible to take Tosafot’s concern of retention of heat and use it in a formalist definition as well.]
Now, all of the above are discussions around the melakha of cooking on Shabbat. How does this apply to the world of ta’arovet, mixture of kosher and non-kosher foods. In this world, our concern is not a cooking process (unless we are talking about the Biblical prohibition of cooking meat and milk together). Our concern is whether – in the real-world – taste transfers from one food to another – from the pork into the chicken soup. Here, a formalistic definition of the process of cooking would be irrelevant. Similarly, the concern for retention of heat should be less, because transfer of taste does not take the same amount of time as it does to actually cook something (consider how long it takes to cook a roast in contrast to when the slices of potato with the roast have a meaty taste). So, what we should find here is that taste transfers regardless of the vessel, and perhaps even in temperatures lower than yad soledet bo. Such is actually the position of Ramban (Avoda Zara 74b, s.v. vi’Od) and Rashba (Torat HaBayit 4:1. 1b-2a), and it is important to note that nowhere in all of the Talmudic discussions regarding transfer of taste is there any mention of terms keli rishon or yad soledet bo. The only term mentioned for the minimum degree of heat required is roteyach, seething, (Hullin 8b) which may be more or less than yad soledet bo (the Rashba assumes its less, and it seems to be based on the specific case to which it is applied), but it is not the same criterion.
Tosafot, however rules – this is implicit in the debate of Rabbenu Tam and Rashbam, above – that even for transfer of taste one needs a keli rishon and for the water to be yad soledet bo. Interestingly, in terms of psak, not only does Rema rule like Tosafot, but Shulkhan Arukh does as well (Yoreh Deah 105 and 91), both stating that no taste is transferred unless one of the foods is yad soledet bo and unless they are in a keli rishon. This position is somewhat limited by later rulings regarding davar gush, solids, which are considered to retain their heat better than liquids and act like a keli rishon, and regarding the ladle used to extract the soup or stew to also be a keli rishon. Regardless, the baseline psak is that taste does not transfer outside of a keli rishon.
There is real irony regarding the practical halakha that emerges from all of this. In the case of Shabbat, almost everyone (Yeraim excluded) rules that one needs a keli rishon for a process to be considered cooking, and the need for a keli rishon can be explained both on a real-world basis (cooking takes time and retention of heat is needed) and on a formalistic basis (the classic act of cooking is done on a fire, so the process requires a connection to the fire), and Shulkhan Arukh rules that a keli rishon is needed. Disregarding all of the above, we, in practice, do not put uncooked foods in a keli sheni if the water is yad soledet bo. On the other hand, when it comes to ta’arovet, where there is no Gemara that talks about keli rishon, and Ramban and Rashba explicitly state that it is not a factor, and there is no basis – either in real-world terms or in formalistic terms – to require it, we nevertheless rule and practice that transfer of taste does not occur outside of a keli rishon.
What is too explain this ironic, almost illogical, conclusion? It seems that the halakhic weight of the issues may play a factor. Although we rule that ta’am ki’ikar, that taste of forbidden foods is forbidden, it is probably not the same prohibition as the food itself, and according to some may, under certain circumstances, not be Biblical. Certainly, in terms of the religious psyche, it is not as weighty as eating pork itself, and it is certainly not as weighty as violating Shabbat. To cook on Shabbat is a profound violation, both objectively and psychologically, and thus it is not surprising that we find a more stringent approach in terms of practical halakha. Another factor, one suggested by my student Mishael Zion, is that our practice on Shabbat relates to how we act lichatchila – we don’t put uncooked food into a keli sheni. Our position regarding ta’arovet – that a mixture in a keli sheni is not a problem – relates to the b’dieved situation: the mixture already occurred. And, in fact, when it comes to the lichatchila question the answer is the same – one should not, li’chatchila, put treif food in a keli sheni with hot kosher food. So the practices can be seen as consistent.
Nevertheless, it is still bizarre that we care about keli rishon in the field of ta’arovet when the only concern should be a real-world one. In practice, I have no problem with the keli rishon criterion when it comes to transfer of taste in and out of vessels. As we discussed in a previous post, one can understand that the issue with non-kosher vessels is also a formalism – defining the vessels as treif and prohibiting their use – and thus we can say that unless they are used in a cooking-like act, their status, and the status of the food in them, does not change. However, when it comes to the actual mixture of two foods -pork falling into the chicken soup – I have a hard time with the keli rishon criterion, and I would look more closely at all the real-world specifics of the case (how long did it stay in? how hot was the soup – boiling or just very hot?, etc.), and take these into account before paskening whether the taste transferred.
What is clear is that even in the world of taste of foods and their transfer, formal halakhic definitions do matter.