Orthodox Conversion to Judaism
Forbidden mixtures
They can not be cooked together.
If hey were cooked together, they are forbidden to eat.
One cannot even derive benefit from this forbidden mixture.
If you have a pet, you may not feed them the mixture.  This is a common problem with dog and cat foods (which often contains cheese, whey and beef.)

Once meat is eaten, one must wait 6 hours before eating dairy.  This is common practise amongst most Jews. 

Dairy food is often refered to as milchig and meat food as fleishig.  Things used in the preparation of these items are also often refered to as this.  Israelis and sephardim tend to use the terms chalavi for milk and basari for meat.

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.  However most restaurants are either one or the other, anyway.

In order to observe the above laws carefully, we use seperate utensils.  It is therefore necessary to keep one set of cookware and utensils for dairy use and another set for meat use.
Meat and dairy....
Meat and fish...
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 in.
When a person eats fish, and then meat, or the opposite, he should eat some bread and drink something in between.  Thus, it will be as if he had cleaned and washed out his mouth.
One must be carefull for human sweat, for all human sweat is like poison, with the exception of sweat from the face.  Therefore, a person should not place food between his clothes and skin because of sweat.  Similarly, a person should not place coins in his mouth, because they might have come sweat upon them.  Furthermore, they are handled by many people and may carry infections.
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