World-class chefs are now using sous-vide water ovens to create the perfectly cooked steak and other foods. The word sous-vide is French and literally means “under vacuum.” This unique technology places food in vacuum packed plastic bags and immerses them in a basin full of water, cooking it at a lower temperature than usual over an extended period of time similar to regular slow cookers. The water is heated to an exact temperature of the chef’s choice.
There are three main benefits to using this technology. Firstly, food such as steak is cooked equally on the inside and outside when using this method, alleviating the problem that sometimes arises when cooking it normally of overcooking the outside while the inner parts are underdone. Secondly the vacuum pack retains the fluids and fats that often dissipate in regular cooking methods, giving the food greater taste and retaining the nutrients. Thirdly, since the temperature is set, one can go about one’s other chores without having to constantly worry whether the food is burning or not.
As mentioned above, the sous-vide usually cooks at a temperature much lower than any other method of cooking.
As this appliance becomes more widely used, a number of halachic queries have arisen in terms of the permissibility of this appliance for Shabbat and its use for both meat and dairy. This article will focus on the latter issue.
- Can the appliance be used to simultaneously cook vacuum-packed meat food together with vacuum-packed milk food?
- If we conclude that one cannot place the milk and meat packets in the basin simultaneously, may one place them there at least one after the other?
In order to answer these questions, we must examine how flavor is transferred between vessels and if there is a distinction if the flavor is transferred in an indirect manner.
Transfer of Flavor Through Heat
Although the Talmud mentions different ways to transfer flavor, the most common one is through heat. The Shulchan Aruch rules: “The heat of a kli rishon (a pot that was at one time directly on the fire) with a temperature of yad soledet bo cooks and prohibits the entire contents of the pot [if a prohibited food is inside].” The crucial temperature is yad soledet bo, which literally means “the hand recoils” due to the heat. Modern day poskim have debated what is the exact temperature of yad soledet bo. The Chazon Ish and Ohr L’tzion held that one needs to be stringent from 40 degrees Celsius, whereas Rav Moshe Feinstein was stringent from 43.3 degrees Celsius. Rav Shlomo Zalman Auerbach ruled that the critical temperature was 45 degrees Celsius, and it is stated in the name of Rav Aharon Kotler that he was lenient up to 49 degrees Celsius.
Most times the sous-vide appliance is set higher than these minimal temperatures and therefore we have to be concerned for the transfer of taste. However, even if it is less than these temperatures, (i.e., less than 40 degrees) there is still room to be stringent. Since the packages sit in the basin filled with water and the heating filament is in this basin, it is considered as if it is a kli rishon that is on the fire. Some Acharonim are stringent in such a case even if the temperature is less than yad soledet bo. Hence, it seems that we should assume that flavor would be transferred even in temperatures below 40 degrees, and definitely above 45 degrees, which is yad soledet bo according to the majority of poskim mentioned.
The Status of the Packaging
Everything stated above is applicable when cooking a meat food directly in a milk pot or vice-versa. Our scenario is slightly different though in that both the foods are sealed in vacuum packages. How does this affect the halacha?
If we view the vacuum packages as separate pots, the case is then parallel to where two pots are on the stove touching each other with liquid present in between them. In such a case, the flavor transfers from one pot to the other. Furthermore, if a drop of milk spilled on the outer wall of a meat pot on the fire in a location opposite that of the food in the pot, the food in the pot needs to be sixty times more than the spill in order to nullify it. This is based on the principle taught in Masechet Zevachim that “bishul mefa’ape’a” – cooking causes the flavor to permeate completely, even through the pot. Hence, although the food might be in packages, which are viewed as vessels, we have learned that flavor permeates these vessels and is then transferred to the other side of the vessel, where there is liquid. Since the packages are both immersed in water, it would seem clear that this would clearly be prohibited, as the meat flavor would be mixed with the dairy flavor and prohibit both packages.
Cooking Meat Packages After the Dairy Packages
Although as we have seen above, it would be prohibited to place the milk and meat packages simultaneously in the sous-vide appliance, as the flavor is transferred from one package to the other, one may still ask whether it would be permitted to place them inside one after the other.
Assuming the water is changed, this case might be likened to the principle in halacha known as nat bar nat (notein ta’am bar notein ta’am). What is this principle exactly?
The Gemara states that “fish that alu in a pot, Rav prohibited them to be eaten with a cheesy dip, and Shmuel permitted it. Rav prohibited it as it notein ta’am, yet Shmuel permitted it as it is notein ta’am bar notein ta’am”. The Gemara concludes that the halacha follows Shmuel. The Rishonim debate the meaning of alu and what the principle of notein ta’am bar notein ta’am means. Rashi explains that alu refers a case where the fish was cooked (or fried) in a meat pot, and the novelty of Shmuel is that this fish can still be eaten with milk. The reason is as follows: When the meat was cooked in the pot, it transferred the meat flavor to the pot (notein ta’am). When the fish was later cooked in the pot, the pot transferred flavor to the fish (bar notein ta’am). This second flavor is now in the fish and is too weak to mix with the milk and cause a prohibited mixture. This is what is known as notein ta’am bar notein ta’am — it transfers the primary flavor, which then transfers a secondary flavor.
Meat Pot Fish Milk
This leniency known as nat bar nat, as explained by Rashi, is codified by the Shulchan Aruch. The Rema rules though that this leniency only applies if the fish has already been mixed with the milk but otherwise it would be forbidden.
In addition to the distinction drawn by the Rema between lechatchila and bedi’eved mentioned, there is also a discussion among the Acharonim as to the significance of lechatchila and bedi’eved in the context of the opinion of the Shulchan Aruch.
Some understand that the Shulchan Aruch only permitted eating the fish with the milk once the fish had already been cooked, but one could not plan to cook a pareve food in a meat pot in order to eat it with milk. Rav Ovadia Yosef argues though that according to the Shulchan Aruch this would be permitted. There is also a discussion as to the Rema’s position if the vessel was not ben yomo.
In the case of the sous-vide, one could argue that when one places the meat package into the water, the package receives the primary flavor, which is then transferred to the water as a second flavor, which in turn transfers this to the actual basin. After changing the water and then placing the milk package in the basin, the meaty flavor from the basin is now transferred to the water, which is in turn transferred to the package. There is good reason to say that since there are a number of nat bar nat transfers here, it might be permitted according to the Shulchan Aruch. Moreover, it is possible that since there seem to be many more nat bar nats in our case, perhaps even the Rema would permit.
However, Rav Tzvi Pesach Frank explains that our analogy is incorrect. Rav Frank in his responsa was asked about a certain yeshiva that wished to keep their milk and meat food hot by placing them in a large basin that had a heating element underneath it. He ruled that not only was it prohibited to heat them simultaneously, but even one after the other. Although this seems like a case of nat bar nat, Rav Frank quotes the opinion of the Chavot Da’at that this is only true when it is not on the fire. But when it is actually cooking, we do not apply the principle of nat bar nat, but view it as if the flavor was directly transferred. Although he quotes Rabbi Akiva Eiger as appearing to disagree with the Chavot Da’at he ultimately rules stringently.
The Status of Vacuum Packages
Even if we accept the opinion of the Har Tzvi, perhaps our case is different. Scientists claim that vacuum-packed packages are not as porous and do not transfer flavor, as opposed to regular pots made of metal and other materials. If so, could we rely on this and permit cooking meat after dairy or even simultaneously? The poskim have yet to rule on this issue, and so this article will remain in the category of “tein lechacham v’yechkam od,” “give a wise man [a little wisdom], and he will become wiser [on his own]” (Mishlei 9:9) discussing the ideas without offering a definitive conclusion.
 Chullin 97a, including kavush k’mevushal, etc.
 Shulchan Aruch, Y.D. 105:2
 This is definitely true for a kli rishon, but concerning a kli sheini, there is an opinion that even if it is yad soledet bo, it might not have the ability to cook or even transfer flavor (Rashba, Torat HaBayit).
 Chazon Ish 37:6
 Ohr L’tzion Vol.2, p.236
 Igrot Moshe, O.C. 4:74:3 and Y.D. 2:52
 Minchat Shlomo 91:8
 See, for example, Pitchei Teshuva 94:1, who brings this stringency in the name of the Maharshal and Chavot Yair, based on the Yerushalmi. Although the Torat Chatat quoted there is lenient, the Shach (105:5) is stringent that there is at least a minimal absorption of kedei kelipa.
 See Mordechai (Chullin, Perek Kol Habasar, Remez 691), who is lenient where there is no liquid between the two pots. However, where there is liquid between them, it is clear that the flavor transfers and prohibits it. This is codified by the Rema in Y.D. 92:8.
 There is a machloket between the Semak and the Maharam of Rotenberg exactly how much is needed to nullify this spillage. However, in our case it is irrelevant as the entire package is filled with food and there is definitely not enough to nullify the taste.
 Zevachim 96b
 Chullin 111b
 Rashi, according to Tosafot and Ra’avan. The Rivan, though, understood Rashi differently. Nevertheless, the Shulchan Aruch rules in accordance with how we have explained Rashi above.
 Shulchan Aruch, Y.D. 95:1
 This includes the Shach, ibid. 1; Pri Chadash 1; Aruch HaShulchan 5, among others.
 Halichot Olam, p.79, se’if 12
 The Gra holds that it would be permitted lechatchila to use a non-ben yomo meat pot to cook pareve food in order to eat it with milk. The Chochmat Adam (48:2) argues that even this would be prohibited lechatchila according to the Rema.
 Responsa Har Tzvi, Y.D. 89
 It should be noted that not all vacuum packages are the same. The sous-vide can be used at home with even a zip-lock, which is completely different than industrial level vacuum packages. The claim of the scientists cited here was made about industrial level vacuum packages.
 See the article in Techumin 34 by Dror Fixler and Yair Frank, p.117.
 The Responsa B’mareh HaBazak dealt with this question and in certain cases did rely on this scientific finding.