Goal of the Class

The goal of this class is to transition from basic background principles/ laws of basar b’chalav to understanding a number of common basar b’chalav issues that arise during cooking in the kitchen.

Issue of Basar b’Chalav when using the Stovetop

Stovetop Grates

The Mishnah Brurah and Rav Moshe Feinstein permit the use of the same stove top grates for both meat and milk based on the presumption that the flame reaches the grate and burns away any “mamashos” of food. If you happen to see some food on the grate then you should wipe it away before placing the other type of pot on there. Dayan Weiss contends that this presumption is not safe enough to rely on and therefore encourages the purchase of separate grates or the “yichud” of certain grates for use only with one type.

Electric Stove Ranges

  1. Without Glass – Open Coil – The halacha follows the same pattern as above by grates
  2. With Glass – Covered Coil – Here there is more need for concern of treif. If one uses the ‘burner’ for both the presumption is that through spillage of both types on one area that area becomes treif. This in turn will treif up the pot used there if it is ever “wet” in any significant way while a pot is sitting upon it. Provided it was always known to be dry we won’t treif up bidieved but there is much more of a need in this situation to designate one burner for one type of food. There is more room to be lenient here also since some poskim hold that glass doesn’t absorb and become treif.

Pots Cooking on Top of the Stovetop

  1. Touching – The golden rule is that two dry pots that touch one another don’t transfer tastes to one another. Therefore a meat pot and a dairy pot cooking on the stovetop together that “touch” don’t create a problem. It should be avoided l’chatchilah though. Furthermore if there is steam on the side or any liquid then it becomes a “shaylas chacham” (some may treif up, some may rely on bitul b’shishim against small amt of liquid, some may ignore bidieved)
  2. Two Open Pots Near Each Other – The Shach holds that it is assur l’chatchilah to put open pots next to one another cooking on the stove top since splattering may occur. Some disagree with the Shach but we don’t rely on them l’chatchilah.
    • Steam Contact Above and Between Two Pots – The same concern applies even when splattering is not practically going to happen but “steam contact” from both pots will.
    • Rising Steam to a Nozzle– A spout on an urn could easily become a kashrus issue if it absorbs steam from one cup below it that had dairy and another that had meat in it since the steam that rises could have still been hot when it rose to touch the nozzle)
    • Steam Rising to things Hanging or Suspended over the Pot– This principle should cause us to be aware of things like low hanging stove hoods, covers, or fans. We should be careful as well for salt and spice shakers held over the pots, as well as “utensils hooks” suspended above a stovetop
  3. Splattering – When we arrive to judge a situation in progress we don’t automatically assume that splattering has happened (even by open pots). If the pots were covered then we for sure don’t worry that splattering occurred. Some have the custom to put a tin barrier in between different type pots cooking on the stove as a precaution.Milk or meat spilling into pot of other type – This is a very detailed topic. For our purposes it is important to know that the basic rule of spillage is as follows. If a solid piece of meat falls into a dairy (liquid) pot while cooking then you must first remove the meat and the remaining milk will either be treif or mutar depending on whether there was 60 parts of milk against the volume of the piece of meat that fell in. If a drop of milk fell into a pot with meat cooking in it then there are certain distinctions that can make a difference and you need to keep them in mind when asking the Rav. Did the drop fall straight into the tavshil or onto a piece that was protruding? Was the tavshil stirred immediately after the drop fell in? Was there sixty parts of the protruding meat against the drop? Was there sixty parts in the tavshil against the drop that fell in?
    • If Splattering Definitely Occurred – This poses a complex halachik question and a Rav should be consulted. The important details for presenting the question are 1) How much splattered approximately and what is the approximate size of the pot that got hit, 2) Did it splatter on a pot that was cooking, 3) Did the splatter hit the side of the other pot or the top, 4) Was the place that the splatter hit above or below the “food level” in the other pot? We can have a whole shiur dedicated to this if you want one.
  4. Stirring pots with opposite type ladle or utensil

Basic Factors to Note when Formulating a Shayla

  1. Status of ladle and pot (meat , dairy, pareve)  – see below
  2. Size of pot and amount of food in it
  3. Depth to which the ladle was inserted and size of ladle
  4. Was the ladle a ben yomo or not – see below
  5. Was the tavshil yad soledes – If not, then assuming the ladle was clean everything is mutar b’deved and don’t refer to below cases.
  6. Was the ladel clean – If not then the shaylah is more complicated than the below rules – (see above in spillage)


  • Ben yomo ladle into opposite type food – The ladle is treif. If the food had sixty against the volume of the ladle that was inserted it and the below pot remain kosher.
  • Ben yomo ladle into ben yomo pot with pareve food cooking in it – Sefardim are more meikal in this case. Ashkenazim hold that you need sixty in the food in the pot against the amount of ladle that was inserted. If not the food, the ladle, and the below pot are all treif.
  • Aino ben yomo ladle into ben yomo pot with pareve food cooking in it – The food and the below pot are mutar. The food however, should be eaten only together with foods that are the same type as the ben yomo pot unless there was sixty in the food against the amount of ladle that was inserted. The ladle  should be kashered.
  • Aino ben yomo ladle into opposite type food – The ladle needs koshering regardless of how much went in or how much food there was. The food is mutar even if there wasn’t sixty in the food against the ladle.
  • Ben yomo ladle into pareve pot – If there is sixty in the food then everything is mutar. If there is less than sixty then the food shouldn’t be eaten with the opposite type of food than what the ladle was.
  • Issues of Basar b’Chalav when Using One Oven for Both Meat and Dairy

Ideally one should have separate ovens for meat and dairy if this at all possible. When it is not there are three main issues to be concerned about in the usage of the same oven for meat and dairy

Contact (Negiyah)

Two foods meat and dairy that touch each other in an oven will lead to part or all of the foods becoming assur (though may not be real derech bishul min hatorah). We must be concerned for gravy or melting dairy oozing across or dripping below to the other food. Another contact issue is one of splattering from two foods or two pots of food in the oven.

Aroma (Reicha)

The general rule of aroma or “reicha” is that l’chatchilah we are concerned that aromas will transfer and thus we avoid cooking any meat and milk (or treif and kosher – or kosher in a treif oven) together in the same oven at the same time even when touching is definitely not an issue. However with regards to our ovens which are large and we commonly open them during use, any time this question of reicha arises, post-facto we will be lenient to allow the foods to be eaten. This leniency will not be so simple in microwaves since there we do not commonly open them during use and they tend to be smaller. If one or both of the foods are in a closed pot then we can be lenient even l’chatchilah.

Steam (Zeiah)

There is a potentially more serious issue though than reicha and that is one of “steam” or zeiah. When we cook foods (other than dry solids) in the oven, “steam” is emitted from them (some say only liquids or non solid foods emit steam but we aren’t that lenient l’chatchilah). The halachik concern is that steam may have been emitted from the food and then rose and absorbed into the oven surface (if this happened by meat and dairy the oven is potentially treif). In addition there is fear that the absorbed drop (whether meat/ dairy or treif) then could condense and fall back into your food. If a person cooks in covered pots than we don’t need to worry about subsequent uses of the oven and potential zeiah problems.

Kashering an Oven from Meat to Dairy Use

In general, when koshering treif items the rule is “k’bolo kach polto” which means the way it went in is the way it goes out. A form of heating or cooking that you want to use to kasher an item must therefore simulate the type of method similar to the one which is normally used with the utensil you are koshering. With regards to ovens the normal method of absorption is through either steam or spillage. This would have to be simulated with pouring hot boiling water on the sides of the oven. This is not very practical with regards to an oven. Therefore the way to kasher an oven is through a more intense form of kashering (i.e. that of LIBUN). The normal rule with regards to libun is that when the item absorbed “heter” (like meat or dairy alone) then you can use libun kal. This libun kal means to get something so hot that it could singe a piece of straw. In today’s regular ovens this is accomplished by putting the oven on the highest setting for about an hour. If the item absorbed treif taste (i.e. basar b’chalav mamash) then you need libun chamur. This can only be accomplished with a blow torch for seven minutes on every square inch, or a self cleaning oven of today.

Regular Oven

There are poskim who don’t require kashering an oven from meat to dairy use. They hold that the issues of reicha and zeiah are not serious enough to assur subsequent use of the other type. With regards to splattering one must make sure the oven is clean in between intermittent usages. One who wishes to be strict and kasher a regular oven for intermittent meat and dairy use should utilize the following practice. Clean any grease or splatter with a good oven cleaner. Some say to wait twenty four hours (others are lenient with this issue). Put the oven on the highest temp for one hour.

Self-Cleaning Oven

This type of oven simulates a libun chamur and poses no problem. One need not clean the oven out with cleaner first or wait twenty four hours.

Continuous-Cleaning Ovens

These types of ovens don’t reach the same temperature as self clean ovens and therefore are treated like regular ovens with regards to kashering.

Issues of Basar b’Chalav with Microwave Ovens

Basic issues with a microwave

Microwaves have the same three problems we mentioned above by ovens. However, here the zeiah problem is worse because the micro is smaller and has less ventilation. Also the nature of this process of cooking produces more steam and splatter.

Intermittent meat and dairy usage

There is a way to permit using the microwave for both meat and dairy use intermittently. Here is what needs to be done:

  1. Clean off all residue between uses
  2. All meat or dairy foods should be covered (in well sealed paper bag or in micro containers)
  3. Insure no direct contact with food and the bottom glass tray or use separate trays

Kashering a microwave

Some say this is possible and allow it if you clean it well, wait twenty four hours and then boil a cup of water to simulate “k’bolo kach polto”. Other poskim hold this is unkasherable because the filter and vent collect residue and can’t be cleaned out. Also the method of kashering isn’t full-proof since the way the micro absorbs isn’t always just through steam and therefore steaming is not necessarily good enough.

Nat bar Nat (“Secondary Taste” – or nosen ta’am bar nosen ta’am)

Basic Rule and Principles

Nat bar Nat of Issur

The poskim say that the kulah of nat bar nat doesn’t apply when the nat bar nat is treif taste. Some poskim hold that this goes on forever transferring and assuring until there is 60 against the whole previous amount, others say that treif taste is more durable and thus keeps going at least until it is no longer recognizable at all.

Nat bar Nat of Heter

  • Double Transfer at Once – When the food passes two stages during one continual cooking process there is a dispute. The Chavas da’as calls it nat, the Yad Yehudah calls it nat bar nat.
  • Food to Food – The Pri Megadim calls any transfer of ta’am through food tam rishon. The Yad Yehudah is willing to call taste transfer through food a ta’am sheni as long as a kli is involved at one of the steps.
  • Food Boiled in Water – What is absorbed in the pot is still called ta’am rishon l’chatchilah
  • Vessel to Vessel (wetness in between) – With the exception of a l’chatchilah chumrah from the Rema (see ahead) lemaseh the ta’am in each kli is ta’am sheni as it comes out and doesn’t treif up the other kli

Primary Case

The primary case of nat bar nat mentioned in the Gemara is when yad soledes hot fish WAS placed on a ben yome meat plate. The main opinion we hold of in the Gemara says one may eat that fish with dairy in the same bite

Defining Lechatchila

The Gemara is clear that one may not make nat bar nat lechatchilah with intent to eat with the opposite food type. The fear is that you will ultimately come to eat meat and milk together. However if it was done, bidieved you may. There is a disagreement as to how to define lechatchilah:

  • Shulchan Aruch – Once cooked, roasted, or derech tzli has been done it is called bidieved
  • Rema – Only once the pareve has been mixed with the dairy or meat is it called bidieved

Halachic Opinions

There are factors (1) Derech Tzli, (2) Tzli, and (3) Cooking Boiling

  • Rivan / Rashi – Only derech tzli has the kulah of the gemara
  • Rosh/ Smag/ Smak  – derech tzli and cooking have the kulah of the gemara
  • Ramban/ Rashba/ Ran  – All three cases cooking, derech tzli, and roasting have the kulah of the gemara


  • Shulchan Aruch – Ramban
  • Rema
  1. Shach – Halacha is like Rosh and Smak
  2. Chachmas Adam – Halacha is like Ramban
  3. Chachmas Adam – No
  4. Gra- Yes

Ben Yomo / Aino Ben Yomo

  • BY – All of the above is true
  • ABY – Same as above on bidieved level (Rema no need for already mixed), However lechatchilah there is a discussion:

Sharp Foods

  • Cooking (all agree it is ta’am rishon from the pot here, if a lot of oil maybe onions lost charif status first)
  • Cutting w/ clean meat or dairy Knife (discussion about whether taste is ta’am rishon or nat bar nat)
    1. Magen Avraham – Ta’am rishon (as if the whole cutting and sharp food together was a cooking)
    2. Even Haozer – What is in the onion is nat bar nat

Soaking (Kavush) and Nat bar Nat

  • Lechatchila – We are concerned about soaking for 24 hours
  • Bidieved / Shas Hatzorech – we say that by the time 24 hours passed the ta’am is pagum


  • Boil water in meat pot to make coffee
  • Melt margarine in milchig pot to use in kneading challos
  • Served hot fish on a meat plate
  • Fish fried in meat pot/ or on meat grill
  • Potato boiled in meat pot planning putting sour cream/ or pasta w/ cheese
  • Serving pareve foods cooked in meat pot during dairy meal
  • Sharp food cooked in ABY meat pot now or cut w/ meat knife mixed with dairy
  • Boiling water in meat pot to be served in ben yomo dairy cup (no milk) – No diff bet Sef /Ash here