Counters:[1]

Initial custom: It is proper and customary to have separate counters for both meat and dairy uses.[2] This especially applies in commercial kitchens and homes with large families and guests. Doing so prevents many Halachic issues from potentially arising in the kitchen, and saves one the trouble of constantly cleaning the counter between uses. [Some also have a Pareve counter top which is designated for Pareve use. It is best to initially build the kitchen in a way that the dairy and meat counters are in opposite ends of the kitchen, as explained in Halacha 1A.]

If one only has one counter: In the event that there is only one available counter and one desires to use the same counter for both meat and dairy, one must be careful to wash and clean the counter prior to placing any meat, dairy, or Pareve foods that will be eaten with meat or dairy, on to it. [Experience shows that counter dirt is often camouflaged and blended into the counter color, and hence a mere glance, and apparent clean look, does not suffice. One should therefore wipe the counter area with a sponge and then feel with his hands to verify that in truth no residue has remained.] Likewise, one must be careful to never place hot foods or hot pots directly on the counter.[3] A simple solution to avoid the above hassle is to designate the counter for only one use, whether it be meat or milk [whatever is more common in the household], and purchase a separate counter lining made of PVC, plastic, and the like, to be placed on the counter and used for the opposite food. Another option is to designate half of the available counter space for meat use and the other half for dairy use.

Bedieved if one placed a cold dairy pot on top of a meat counter, or vice versa: If a cold meat pot was placed on a counter that contained cheese, or vice versa, then everything remains Kosher and the pot is to be rinsed with cold water to remove any possible residue of dairy products.

Bedieved if one placed a hot meat pot on top of a dairy counter, or vice versa: If a hot [Yad Soledes] meat pot was placed on a counter that contained dairy residue, then the pot becomes forbidden and requires Koshering, although the food that is inside the pot remains Kosher.[4] If the counter was clean but wet, then that area of the counter becomes Treif and requires Koshering.[5] The pot and food, however, remain permitted unless one knows that this area of the counter absorbed hot dairy within the past 24 hours and the counter was wet.[6] If the counter was clean and dry, and likewise the bottom of the pot was clean and dry, then both the counter and the pot with its food remain Kosher.[7]

Bedieved if one placed a dairy food directly on top of a meat counter: Bedieved, if one placed dairy food directly onto a meat counter, everything remains permitted, so long as the food was cold and the counter was clean, and the food did not soak on the counter for 24 hours.[8] In such a case, the counter requires a mere washing in cold water. If, however, the counter was dirty with meat, then the area of the dairy which contacted the food must be washed or peeled off.[9] If the food contains liquid [i.e. milk] and it remained on the counter for 24 hours, then the counter is forbidden and needs to be Koshered.[10] If the counter was clean but the dairy food was hot, then if the food was a Keli Rishon, or Iruiy Keli Rishon, then the counter is forbidden[11] while the status of the food is dependent on whether the counter was Ben Yomo or not.[12]    

Cut a Charif food on a meat counter: See Chapter 5 Halacha 3 in Q&A!

[1] See Hakashrus 1:9-12

[2] Yad Avraham 88 “Nevertheless, the Jewish people are holy and are accustomed to have separate tables for meat and milk.”; Darkei Teshuvah 88:9-11

The reason: This is done in order to prevent possible mixtures of meat and dairy from occurring. Many counters contain leftover foods either due to placing food directly on it, or having food spill. Often, it is difficult to tell that the counter is truly clean and one may come to place a meat food on dairy leftovers or vice versa. This especially poses an issue if one places hot food on the counter, in which case it will absorb the taste of the leftover meat/milk. [See P”M O.C. 173] Furthermore, even if the counter is clean, if it is used for both meat and milk it will most certainly become Treif, either due to spillage of hot meat and milk onto the counter, or due to leftover meat and milk soaking on it for 24 hours in the moisture that is commonly found on the counter. This will then require one to be very careful to never place hot food directly on the counter, including hot pots, as if one does so and the counter is wet, it can prohibit the pot and food, as explained next. [See Admur 451:58; Hakashrus ibid footnote 14]

[3] The reason: As the counter is most likely Treif due to hot spillage, as explained in the previous footnote, and if one places a hot pot or hot food directly on the counter, even if clean, it can prohibit the pot/food, as explained next. Nonetheless, if in truth the counter is clean and dry, then from the letter of the law it is permitted to place a hot dry pot [not food] onto it directly, as explained next.

[4] See Chapter 8 Halacha 16! Likewise, seemingly the counter also remains Kosher as the cheese is in the place of the Kelipa.

[5] This applies even if the counter was clean and not Ben Yomo. See Chapter 8 Halacha 20C

[6] P”M 92 M.Z. 29; Regarding Ben Yomo versus non-Ben Yomo -See Chapter 8 Halacha 2D and 20C!

The reason: As if there is moisture in-between the two materials, it serves as a conduit to transfer taste and prohibit the food.

[7] See Rama 93:1; Taz 92:29; 97:3; Admur 451:41 and 67; 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 103; Erech Hashulchan 92:15 that so is opinion of all Achronim; Chochmas Adam 50:2; Zivcheiy Tzedek 92:79; Kaf Hachaim 92:103; 97:29; See Tzemach Tzedek O.C. 43

The reason: As this is similar to two pots touching each other in which we rule that both pots are Kosher, even though both pots contain absorption of taste of the opposite food. [Taz ibid]

[8] Shach 121:11

[9] See Taz 91:2; Rashal Kol Habasar 44

[10] See Rama 105:1; Chapter 8 Halacha 7!

[11] This, however, only applies if the counter has been used in the past for hot meat, or has been washed with hot meat, or has had meat soak in it for 24 hours. Otherwise, the counter remains Kosher and is now dairy.

[12] See Chapter 8 Halacha 18B-C!