From Wikipedia Kosher foods are those that conform to Jewish law. Invalidating characteristics may range from the presence of ingredients derived from non-kosher animals or kosher animals that were not properly slaughtered, a mixture of meat and milk, wine or grape juice (and their derivatives) produced by gentiles, the use of produce from Israel that has not been tithed properly, or even the use of cooking utensils and machinery which had previously been used for non-kosher food.   Video Source: www.youtube.com