Sous-vide cooking involves placing food in a plastic pouch and cooking in a water bath at a precisely regulated temperature. A video explaining how sous-vide cooking differs from traditional cooking appears at https://www.youtube.com/watch?v=9CeoggmeUkc. Contemporary poskim address various issues regarding sous-vide cooking, including whether we may use the same machine to cook meat and milk without koshering.

Concurrent Cooking of
Meat and Milk in a Sous-Vide

May we simultaneously place an industrial-grade vacuum-sealed bag with dairy and a second industrial-grade vacuum-sealed bag with meat in the sous-vide water bath? One could argue it is permitted because the bags are professionally sealed, so the meat and milk will not mix. Beli’ot and food pieces would seem contained and not contaminate the food from the other “gender.”

However, intuitively, it seems too close for comfort. Indeed, the OU Kosher website (https://oukosher.org/halacha-yomis/may-sous-vide-machine-used-dairy-meat-items/) states we may not mix the meat and milk bags in the same pot. They are concerned because the bags are not completely leak-proof. In addition, the OU’s poskim are not convinced no halachic absorption occurs.

Rav Mordechai Willig (communication to Binyamin Jachter) agrees. Rav Willig explains that it may be an acceptable non-transfer of tastes from a scientific perspective but insufficient for halacha. Rav Willig adds that it is difficult to construct a test to determine if it is a halachically acceptable seal. However, if an industrial-grade bag is used, it seems that only leakage of ta’am (taste) into the water is a concern, not the actual food contents.

Fish and Meat in One Sous-Vide

Because of the concern for leakage, the OU does not even permit simultaneous sous-vide fish and meat cooking. They do, though, allow cooking them consecutively (https://oukosher.org/halacha-yomis/may-fleishig-sous-vide-machine-used-fish-can-cook-fish-meat-machine-time/).

The Gemara (Chullin 111b) and Shulchan Aruch (Y.D. 95:1) permit hot fish placed on a meat place and are not concerned about mixing fish with meat ta’am. The Taz (Y.D. 95:3) observes that we see that Chazal only forbid (Pesachim 76b) fish and actual meat but not fish and actual ta’am. The Chochmat Adam[1] (68:1) codifies the Taz.

Most observant families follow the Taz. Thus, since one changes the water between sous-vide uses, the sole concern is meat ta’am embedded in the walls, which does not pose a problem regarding mixing meat and fish. However, OU Kosher is concerned about more than ta’am leaking into the sous-vide water bath and thus does not permit concurrent cooking of meat and milk.

Consecutive Cooking of Meat And Milk in a Sous-Vide

Our next question is whether we may place meat and milk in separate vacuum-sealed bags and place them in the sous-vide at different times. It seems permissible since it is a case of permitted nat bar nat d’heteira, taste which comes from taste, (all agree that a three-step nat bar nat is allowed, Shach Y.D. 94:15).

Five permissible steps separate the meat and dairy food using the same sous-vide. For example, the meat is absorbed into the sealed bag, the water and the machine’s walls (three steps). When the dairy bag is placed in the water, the meat beli’ot absorbed in the machine’s wall first enters the water and then the sealed bag before it enters the sealed bag containing milk.

However, OU Kosher’s poskim note that the Chavat Da’at (95: Bi’urim 2, cited by the Pitchei Teshuva Y.D. 95:1) and Rabi Akiva Eger (in a responsum published at the end of his Derush V’chidush) believe it does not qualify as nat bar nat since the taste transfers occur simultaneously. In the classic case of nat bar nat, one cooks meat in a pot, and only later does one cook a pareve item. The taste transfers from the meat to the pot and the pot to the pareve item do not occur simultaneously. The sous-vide does not match the classic nat bar nat since the taste transfers simultaneously. Thus, it is the equivalent of the meat being absorbed directly into the sous-vide wall and then directly back to the milk (i.e., it is the equivalent of cooking milk in a meat pot). Shulchan Aruch 92:5 seems to support the Chavat Da’at.

However, Pri Megadim (Y.D. 95: Mishbetzot Zahav 2) disagrees with the Chavat Da’at and applies nat bar nat in this case. The Pitchei Teshuva also cites Teshuvot Beit Ephraim (Y.D. 37), who is lenient, as is the Pri To’ar (95:4).

Shulchan Aruch Y.D. 95:2, as explained by the Be’er Heitev (Y.D. 95:4, citing the Rashba), supports the lenient view. We may not eat an unshelled egg cooked in a pot with meat because its shell is porous. This Rashba implies that if the shell were not porous, it would be permitted to eat the egg with milk since it constitutes nat bar nat (meat taste absorbed into the shell, which the shell then imparts to the egg) even though it is cooking simultaneously. The Beit Efraim also cites the Shach Y.D. 94:15) to support his view. The Aruch Hashulchan (Y.D. 95:4) and Badei Hashulchan (95:7) conclude with uncertainty regarding whom we follow.

Rav Ovadia Yosef (Halichot Olam 7:79 and Yalkut Yosef 95:7) follows the lenient view. It is not surprising since Rav Ovadia places no limitations on the nat bar nat principle. Thus, Sephardic Jews may cook consecutively meat and milk in sous-vide since Rav Ovadia does not codify the Chavat Da’at followed by OU Kosher.

Conclusion: Ashkenazim Eating at Sephardim Who Use a Sous-Vide for Consecutive Meat and Milk Uses

Simultaneous use of one sous-vide for milk and meat is not permitted. Sephardic Jews may use a sous-vide consecutively for meat and dairy, but Ashkenazim may not. However, b’dieved (after the fact) even an Ashkenazi may eat dairy cooked in a sous-vide previously used to cook meat, even if it was cooked within the prior 20 hours if the foods were cooked in an industrial-grade vacuum-sealed bag. In such a case, we have a s’fek s’feika (double doubt), one safek (doubt)is perhaps the seal prevents meat ta’am from leaking out of the bags (a safei set forth by Rav Moshe Feinstein in Teshuvot Igrot Moshe Y.D. 3:14). The second safek is maybe we follow the Pri Megadim, Teshuvot Beit Ephraim, and Pri To’ar ruling that even simultaneously cooking qualifies as nat bar nat.

Rabbi Jachter serves as the rav of Congregation Shaarei Orah, rebbe at Torah Academy of Bergen County, and a get administrator with the Beth Din of Elizabeth. Rabbi Jachter’s 17 books may be purchased at Amazon and Judaica House.