In addition to food ingredients being kosher, the equipment used in food processing must also be kosher. Equipment used to manufacture products containing non-kosher ingredients may acquire a non-kosher status. Thus, production that takes place after non-kosher production is completed, can be rendered non-kosher by virtue of the equipment used, even if the ingredients are kosher.
Non-kosher equipment usually can be restored to a kosher state in a variety of ways, usually depending upon the production process of non-kosher items. This process is referred to as Kosherization. The laws regarding what equipment can be kosher and under what circumstances they can be kosher are complex. Therefore only a trained Rabbi is competent to oversee the procedure. Usage of a non-kosher product in conjunction with liquid, e.g., a non-kosher soup, requires a thorough cleaning and the use of boiling water in order to restore its kosher status. Non-kosher products that were produced where there is no liquid cooking medium, e.g., an oven band, require a different technique. This equipment must be treated with high heat in order to restore its kosher status.