The Jewish religion has strict rules regarding food that is considered acceptable to eat. These rules affect both the ingredients of a food and the way a cook prepares the food. For these reasons, even though the ingredients of a donut may be kosher, if a baker made it in a kitchen that does not follow specific rules, then the donuts are not considered kosher. Kosher donuts are those that were prepared adhering strictly to the rules, and devout Jewish people therefore find them acceptable to eat.
Kosher donuts must have all kosher ingredients. Typical ingredients of a donut include flour, salt, and eggs. Milk and sugar are also added, and yeast promotes the rise of the dough. These ingredients are not intrinsically non-kosher.
Most basic foods can be kosher, with the major exception of common foods like pork, shellfish and certain varieties of fish, including catfish. As well as a prohibition on certain foods, kosher food authorities state that a cook cannot prepare dairy products and meat together. A donut that contains animal lard instead of butter, for example, along with milk, would not be kosher.
Sometimes the ingredients seem kosher at first glance. Complex causes of non-kosher ingredients include such situations as a filling that contains animal glycerin. Consumers may only know a donut is kosher if the manufacturer has certification from a kosher authority.
Food preparation areas that are kosher require the workers to follow certain practices inside the kitchen. These include the rule that a cook may not use a utensil for a kosher purpose and for a non-kosher purpose. He or she cannot handle kosher donuts with a spatula, for example, and also use the same spatula to handle bacon strips.
This prohibition also extends to the equipment inside the kitchen, or in the manufacturing process. If the ingredients of the donut contain fat that a manufacturer has treated with a particular machine, but previously produced animal fats using that same machine, then the entire donut would not be kosher. Inside the preparation area, all equipment, including the baking trays, have to be restricted specifically to non-kosher and kosher use. Sinks, stoves and dishwashers are all common pieces of equipment where kosher practices can come into contact with non-kosher practices.
As keeping food kosher is a complicated process, many commercial establishments do not attempt it. Some donut franchisers may provide kosher donuts, but if franchise owners demand that the business sell the entire range of the products, then staying kosher becomes impractical. A menu that includes bacon, for example, will not fit within kosher guidelines in practicality.