Meat is only the beginning
The origin of the meat is the best-known condition, but on its own it says little. What matters is the whole chain: purchasing, storage, preparation and serving. Halal-certified meat cooked in the same fryer as a non-halal product no longer meets the standard your guests have in mind.
Alcohol is the most common gap
Alcohol turns up in a kitchen in places you do not think of first: as a wine reduction in a sauce, rum in a dessert, deglazing a pan, an ingredient in bought stocks and marinades. A kitchen working consistently alcohol-free has to decide that at purchasing, not at the stove.
Our restaurant kitchen in Köpenick has worked fully halal and alcohol-free since 2010. It is not a separate catering line but how the house works generally — which is why there is no parallel production here from which the wrong thing could accidentally reach the tray.
What to ask a supplier
Is the entire kitchen halal or only one line? Is alcohol used in the house — including for cooking? Are there separate fryers, boards and equipment? Which supplier does the meat come from? Is there a certification, and from which body?
A supplier who dodges the last question is not automatically dishonest — many small operations are not formally certified but work cleanly. A supplier who cannot answer the first three clearly should give you pause.
For mixed guest lists
The practical advantage of a fully halal kitchen is that nobody gets a special meal. There is one buffet and everyone stands at it. Those observing for religious reasons do not have to ask; those who are not notice no difference. That is exactly the point.