On three separate occasions, the Torah tells us not to "boil a kid in its mother s milk." (Ex. 23:19; Ex. 34:26; Deut. 14:21). The Oral Torah explains that this passage prohibits eating meat and dairy together. The rabbis extended this prohibition to include not eating milk and poultry together. In addition, the Talmud prohibits cooking meat and fish together or serving them on the same plates, because it is considered to be unhealthy. It is, however, permissible to eat fish and dairy together, and it is quite common. It is also permissible to eat dairy and eggs together.
This separation includes not only the foods themselves, but the utensils, pots and pans with which they are cooked, the plates and flatware from which they are eaten, the dishwashers or dishpans in which they are cleaned, and the towels on which they are dried. A kosher household will have at least two sets of pots, pans and dishes: one for meat and one for dairy. See Utensils below for more details.
One must wait a significant amount of time between eating meat and dairy. Opinions differ, and vary from three to six hours. This is because fatty residues and meat particles tend to cling to the mouth. From dairy to meat, however, one need only rinse one s mouth and eat a neutral solid like bread, unless the dairy product in question is also of a type that tends to stick in the mouth.
The Yiddish words fleishik (meat), milchik (dairy) and pareve (neutral) are commonly used to describe food or utensils that fall into one of those categories.
Note that even the smallest quantity of dairy (or meat) in something renders it entirely dairy (or meat) for purposes of kashrut. For example, most margarines are dairy for kosher purposes, because they contain a small quantity of whey or other dairy products to give it a dairy-like taste. Animal fat is considered meat for purposes of kashrut. You should read the ingredients very carefully, even if the product is kosher-certified.
Utensils
Utensils (pots, pans, plates, flatware, etc., etc.) must also be kosher. A utensil picks up the kosher "status" (meat, dairy, pareve, or treyf) of the food that is cooked in it or eaten off of it, and transmits that status back to the next food that is cooked in it or eaten off of it. Thus, if you cook chicken soup in a saucepan, the pan becomes meat. If you thereafter use the same saucepan to heat up some warm milk, the fleishig status of the pan is transmitted to the milk, and the milchig status of the milk is transmitted to the pan, making both the pan and the milk a forbidden mixture.
Kosher status can be transmitted from the food to the utensil or from the utensil to the food only in the presence of heat, thus if you are eating cold food in a non-kosher establishment, the condition of the plates is not an issue. Likewise, you could use the same knife to slice cold cuts and cheese, as long as you clean it in between, but this is not really a recommended procedure, because it increases the likelihood of mistakes.
Stove tops and sinks routinely become non-kosher utensils, because they routinely come in contact with both meat and dairy in the presence of heat. It is necessary, therefore, to use dishpans when cleaning dishes (dont soak them directly in the sink) and to use separate spoon rests and trivets when putting things down on the stove top.
Dishwashers are a kashrut problem. If you are going to use a dishwasher in a kosher home, you either need to have separate dish racks or you need to run the dishwasher in between meat and dairy loads.
You should use separate towels and pot holders for meat and dairy. Routine laundering kashers such items, so you can simply launder them between using them for meat and dairy.
Certain kinds of utensils can be "kashered" if you make a mistake and use it with both meat and dairy. Consult a rabbi for guidance if this situation occurs.
