Using the same stove top for cooking meat and milk:
It is highly recommended to have two separate stoves for meat and dairy in order to avoid possible Kashrus complications that can arise when sharing the same stove for cooking both meat and milk. If one is unable to purchase a separate stove top, he is at the very least to purchase separate grates for meat and milk which are to be alternated for the cooking of meat and dairy products. Alternatively, rather than buying two sets of grates, some of the grates should be designated for meat use while the others for dairy use. Alternatively, one can use the grates for one food and place a metal grate cover over the grates when cooking the opposite food. The above is all in accordance to the initial and recommended practice, however, from the letter of the law, it is permitted to use the same grates for cooking both meat and milk, so long as certain guidelines are followed:
The necessary precautions when using the same grates for meat and milk: If one desires to use the same grates for both meat and milk, one must beware of the following matters:
- Clean: One must verify prior to each use that there is no residue of food left on the grates [or bottom of the pot]. [Thus, the grate should be cleaned with soap and water. A mere glance does not suffice to detect oil and fat residues. One is not to suffice with simply turning on the flame to burn any residue, as often the flame does not reach all areas of the grates.]
- Dry: One must verify that both the grates, and the pots being placed on the grates, are completely dry. [The pot bottom should be dried with a towel if wet, while the grates can be placed on the stove top and dried through turning on the flame, prior to resting the pot on it. It is advisable to leave a towel in close distance from the stove top to use for the drying.]
- Spillage: The pot is not filled and heated in a way that will cause spillage onto the grates upon it reaching a boil. If in the event of the cooking the food boiled over and spilled towards the grates, hence making them wet, then this follows the same laws as one who cooked with a wet pot or grate, as brought below!
- One may never place any foods [as opposed to pots] directly on the grates, as the grates themselves are considered Treif and can transfer forbidden taste to the food even without liquid. One may, however, place the food on tinfoil and then rest it on the grate.
Bedieved if one cooked dairy on a meat stove top grate which was dirty or wet or vice versa? If one cooked a dairy pot of food on grates that were visibly dirty from meat, the pot and its content are forbidden unless the food contains 60x versus the meat residue, in which case the food is permitted while the pot must be Koshered. If the grates were clean but wet, or the bottom of the pot was wet, or the pot boiled over onto the grates, then if the grates had not had meat cooked on them in the past 24 hours, the dairy food and pot remains permitted. Furthermore, even if a pot of meat was cooked on the grate within the past 24 hours, the food is permitted if one does not know for certain that meat food spilled on it within the past 24 hours. If, however, one knows for certain that meat spilled on it within the past 24 hours, then even if it is now clean, according to some Poskim the food is possibly forbidden.
Cooking meat and milk on different grates at the same time: Initially, one is to avoid cooking meat and dairy foods next to each other on the same stove top at the same time. Nonetheless, if one did so, everything remains permitted so long as no spillage was witnessed. This applies even if both pots were uncovered and released steam, and applies even if the pots were touching each other [if the pots were dry]. When cooking in such a way, extra care must be taken when mixing the food and lifting up the covers, to avoid spillage onto the opposite pot.
The status of the grates and stove top area if used to cook meat and milk: In all cases that the same stove top is used for cooking meat and milk, [irrelevant of whether the same grates are used] the stove top area under the grates is considered not Kosher due to spillage of hot meat and milk. Therefore, one may not place any food there. If food falls onto the stove top while hot, the food is forbidden unless the stove top is clean and has not received spillage within the past 24 hours. Whenever the same grates are used for both meat and milk, per the guidelines set about above, the grates are considered Treif and any hot food that falls on them is forbidden unless the grate is clean and not Ben Yomo of spillage, as stated above regarding the stove top.
 See Hakashrus 1:20-30
 The potential complications: See the conditions listed below of which a lack of adherence to those conditions can prohibit the pot and its contents.
 See Erech Hashulchan 92:15 and Kaf Hachaim 92:103 that it is proper to initially avoid cooking dairy on a meat surface even if the surface area is dry and clean, if the matter is not necessary; Chochmas Adam 74:4; Kesav Sofer Y.D. 54; Teshuvos Vehanhagos 2:387; Hakashrus 1:20
 See Rama 93:1; Admur 451:41 and 67; Taz 92:29; 97:3; Kneses Hagedola 92:73; Peri Chadash 92:36; Minchas Yaakov 56:22; Lechem Hapanim 92:54; 97:1; Halacha Pesuka 97:1; Beis Lechem Yehuda 92:40; P”M 92 M.Z. 29; 97 M.Z. 1; Sheilas Yaavetz 1:103 and 113; Erech Hashulchan 92:15 that so is opinion of all Achronim; Chavos Daas 92; Chochmas Adam 45:19 and 50:2; Zivcheiy Tzedek 92:79; M”B 451:34; Kaf Hachaim 92:103; 97:29; See Tzemach Tzedek O.C. 43; Hakashrus 1:20; Pischeiy Halacha 1:30; Igros Moshe Yoreh Deah 1:40 and 2:59
The reason: a) We do not suspect that milk and meat may have splashed onto the grate, as we are not Machzik Issur. b) Even if it did splash, taste cannot transfer between two materials unless there is heat and moisture in-between. Thus if one abides by the conditions which verify cleanliness and dryness when placing the pot on the grates, there is no issue with the fact that one is cooking dairy on grates that are Treif or meaty. [Poskim ibid]
 See Igros Moshe Y.D. 2:59 who allows using the same grates and does not mention any conditions, as he assumes as writes the M”B ibid that we don’t suspect for spillage, and even if spillage occurred it gets burnt, and the grate gets Koshered through the fire. Vetzaruch Iyun as the M”B statement was said regarding the grates of previous times, in which the coals completely surrounded the grates, however, today the fire does not reach all areas and hence certainly must be cleaned and dry.
 See Beis David O.C. Pesach 208; Zechor Leavraham Y.D. 2; Zivcheiy Tzedek 87:48; Kaf Hachaim 87:65
 See M”B ibid that we can assume that the fire has burnt off all the residue. This was said regarding the grates of previous times, in which the coals completely surrounded the grates. However, by today’s gas stoves, this is not the case. Vetzaruch Iyun from Igros Moshe Y.D. 2:59 who extends the allowance even to today’s stoves!
 The reason: As if they are wet, the forbidden taste that is absorbed within the grates can enter the food.
 See Beis David O.C. Pesach 208; Zechor Leavraham Y.D. 2; Zivcheiy Tzedek 87:48; Kaf Hachaim 87:65; Chapter 8 Halacha 18!
 See Hakashrus 1 footnote 51
 See Shach 92:32; Kneses Hagedola 92:85; Peri Chadash 92:29; Lechem Hapanim 92:47; Beis Lechem Yehuda 92:35; Minchas Yaakov 56:20; Kreisi 92:26; P”M 92 S.D. 32, M.Z. 25; Biur Hagr”a 92:35; Chochmas Adam 45:14; Zivcheiy Tzedek 92:55; Kaf Hachaim 92:80
 The reason: As Ein Machzikin Issura, and hence if one did not see any spillage we do not assume that it occurred. [See Chochmas Adam 45:15; Zivcheiy Tzedek 92:60; Kaf Hachaim 92:84]
 See Rama 95:3 regarding pouring from a Ben Yomo meat pot to Ben Yomo dairy pot. Vetzaruch Iyun if the Michaber ibid who is lenient in that case would be lenient here as well; However, perhaps one can offer an additional reason to be lenient according to all, and that is because the grates are considered Koshered by the flame under them, as the grates only require Libun Kal [unless actual meat and dairy foods mixed while on the rgate], which is accomplished through heating up the metal until Yad Soledes. Accordingly, by the time spillage has occurred the grates have already been Koshered from their absorbed meat.
 See Hakashrus 1:26-27
 See Rama 92:8; Admur 451:65-67; Erech Hashulchan 92:15; Kaf Hachaim 92:103
 P”M 92 M.Z. 29
 The reason: As taste cannot transfer from the material of one pot to another [without moisture in between], and we do not suspect that milk and meat may have splashed into each other, as we are not Machzik Issur. Likewise, there is no issue of Reicha to be worried of. [Poskim ibid]
 If the area that the food fell on contains hot residue or is Ben Yomo, then it requires 60x versus the residue. If the residue is cold but the food is hot, then only a Kelipa is required. See next footnote for sources.
 See Chapter 8 Halacha 18 regarding if the stove top was clean and Chapter 8 Halacha 11 regarding if it was dirty.