Despite some variation in the interpretation of halal requirements, they are generally minor. Main food items that are prohibited (haram) under Islamic dietary laws include: swine/pork and its byproducts, animals improperly slaughtered, alcohol and intoxicants, carnivorous animals, birds of prey, land animals without external ears, blood, contaminated foods and foods containing questionable ingredients such as gelatine, emulsifiers and enzymes.
Preservatives are also questionable food ingredients, as well as other products used in the production of food including processing aids, lubricants, cleaning agents, sanitizers and packaging material.
Genetically-modified organisms and biotechnology raise new challenges for halal certification. Regarding transgenic foods, plant to plant gene transfer is acceptable; however, animal-to-plant or animal-to-animal gene transfer is questionable and may, or may not, be acceptable.