1. The prohibition of meat and milk relating to domestic animals is the following:
a. They cannot be cooked together.
b. If they were cooked together, they are forever forbidden to eat.
c. One cannot even derive benefit from this forbidden mixture. (This is a common problem with dog and cat foods, which often contains cheese, whey, and beef.)
Although these laws extend to fowl as well, the øåñéà of deriving benefit does not apply here. An example of this is dog food, which contains chicken and whey, and is allowed to be used by the kosher consumer for his pets.
2. Once meat is eaten, one must wait a period of time before eating dairy foods. According to most authorities one must wait 6 hours before eating dairy. This is the common practice among most Jews. However, some communities have a tradition of allowing dairy to be eaten following meat after a wait of 1 to 3 hours. People should follow their family tradition. This opinion follows the ruling of Tosfos. This Halacha of separating meat and milk extends even to the point of not allowing two people to eat at the same table while one is eating dairy and the other is eating meat. (When necessary, however, some sort of divider can be placed between them.) This is true only when the people know each other. In the case of two strangers in a restaurant, for instance, this does not apply.
3. The only time that it is necessary to wait after eating dairy foods is in the case of hard cheese. Cheese is considered hard only after being aged for 6 months or longer. Currently in the U.S., almost all cheeses that are available to the kosher consumer are aged only 60 days.
4. Utensils: In order to observe the above laws carefully, we use separate utensils for dairy and meat products. This separation affects cooking utensils as well as eating utensils. It is therefore necessary to keep one set of cookware and utensils for dairy use and another set for meat use. Unfortunately, at times, we find that the two sets of utensils get mixed up and confused. When this happens, it is necessary to consult a competent Rabbi.
Generally speaking, the following rules apply:
a. Cold utensils don’t contaminate each other and when they have been used only in a cold state, they do not require kashering. The exception is if they become kovush, such as in the case where milk drops on a meat plate. If the milk remains there for 24 hours or more, the utensil becomes non-kosher.
b. Even cold utensils that were used for “cold” foods, if the food was of a sharp nature, such as onions, they follow the rules of “hot” foods. This is true only in the case of Duchka Desokino, where a knife was used to slice the food. This is due to the pressure caused by the slicing.
c. In a case where food that was cut by utensils of the opposite type (i.e., a dairy knife cutting hot meat,) the cutting utensil requires kashering. The food may not be kosher depending on its size.
d. Glassware is usually considered pareve and cannot take on the characteristic of either meat or dairy when they are used for drinking or eating but not for cooking. This is true of Arcolac and Corelle. Note: Pyrex is not included in above.
5. The general rules of kashering a utensil are as follows:
a. Only metal utensils can be kashered.
b. We only kosher utensils from dairy to meat or vice versa when they have become non-kosher, or when we are kashering them anyway for Pesach. It is not allowed to kasher from one status to the other (meat and dairy) year round for mere convenience.
c. Plastic, synthetic rubber, melmac, porcelain, pyrex, Corningware, Teflon and Silverstone cannot be kashered.
d. When an article can be kashered, the rule is that “as it absorbed, so it will expel”. Therefore, items used with liquid can be kashered with liquid. However, items used directly “in the fire”, without liquid, such as a cookie sheet, are harder to kasher. These would need to be heated directly with a very hot temperature such as a torch.
6. Dishwashers, according to Rav Moshe Feinstein, ZT”L, can be used for dairy and meat utensils. This is true even with the porcelain lined dishwashers. Care must be taken to clean the drain before switching. However, it is necessary to maintain separate racks for dairy and meat dishes. It is recommended, as well, to run the dishwasher with soap (empty) in between dairy and meat use. This leniency does not apply to using the year round dishwasher for Pesach.
7. Tablecloths and napkins can be used for dairy or meat provided they are cloth and not plastic. The tablecloth must be washed between uses.
8. A hot water urn can be used to place water in dairy or meat utensils. This is only true when the urn is not used for anything other than water or other pareve substances.
9. Sinks should be used separately for dairy and meat utensils. In case of a sink that is not kosher, or when only one sink is available, a plastic tub or insert should be used. Only sinks made of metal can be kashered.
10. A blender or food processor needs separate containers and blades for dairy and meat use.
11. The range (cooktop) can be used for dairy and for meat according to most opinions. The reason is that the metal prongs are always in contact with the fire, making them kosher.
12. A refrigerator and freezer can be used for both dairy and meat products. Care should be taken not to allow anything to drip from the dairy to the meat products or vice versa.
When moving into a new home, where the dishwasher was not kosher, Rav Moshe Feinstein, ZT”L, is of the opinion that one should wait for 12 months before using the dishwasher. During this time, the dishwasher should not be used at all. After 12 months, the dishwasher should be run 3 cycles with detergent. At the completion of this procedure, the dishwasher and racks may be used.
13. There can be a problem when one has a non-Jewish maid in the house. Meat, as well as other kosher items (utensils etc.) cannot be left unattended where a mishap can occur. If the non-Jewish maid knows that a Jew will be coming into the house, periodically, unannounced and unscheduled, this would alleviate this problem. It is highly advisable for one who has a non-Jewish maid to have locks on utensil and food cabinets to avoid this problem. Another alternative is to arrange with a Jewish neighbor to come in at irregular intervals during the day.
14. A toaster oven cannot be used for both dairy and meat. It must be designated for dairy or meat only. Since some companies test the toaster first with non-kosher bread, check for breadcrumbs. If found, ask your Rav what to do.
15. Meat and fish may not be eaten together. Nevertheless, fish may be cooked in either a dairy or meat pot and eaten with the appropriate cutlery corresponding to the status of the pot in which the fish was cooked.
16. If a person is cooking soup with meat in it and tastes it to see if the flavoring is right, and then spits out the soup, without swallowing any, he is considered to be “meaty” (fleishig).
17. Meat vitamins, such as liver pills, do not make a person “meaty”. It is not necessary to wait 6 hours after swallowing these pills.
18. Although normally, it is not permissible for a person to kasher his silverware from milk to meat (or visa versa,) if he receive expensive silverware as a gift, he may kasher it.