Another concern is the conditions in which the food was cooked or prepared. i.e. it is possible that cooking utensils were "un-kosher" due to the fact that non-kosher foods were previously prepared in them. These foods are absorbed in the walls of the utensil, constantly adding non-kosher "flavoring" to all future products prepared in that utensil.

Few food manufacturing facilities are naturally sensitive to the above issues as to be relied upon for our spiritual well-being and the fulfillment of G-d's laws. For example, most cheeses and cooking oils do contain meat derivatives.

Factories often cook meat products in the same vessels as milk products, and rarely do "vegetarian" items undergo the to rigorous check for insects and worms common in the preparation of a meal in a standard kosher household.

[Furthermore, the Sages banned most foods which were entirely cooked by a non-Jew. See What are the rules regarding food which was cooked or baked by a non-Jew?]

If a person can be sure, beyond a reasonable doubt, that a certain uncooked food is truly absent of animal products, insect-free, and prepared in kosher utensils, then kosher certification is unnecessary.

There are certain products -- such as beverages, spices and dry fruit -- which do not require kosher certification. Click here to view some lists of foods which do not require certification.