The Five Grains

• The five forbidden grains for Passover are barley, oats, rye, spelt and wheat. These grains can't be consumed because they might have come in contact with water, which makes them non-kosher. Consequently, all foods which contain any of these grains, like bread, are also deemed non-kosher. Only a special type of bread, called matzo, is allowed. In a similar manner, any type of food which requires yeast is labeled as non-kosher as there might be a chance the yeast was produced from one of the forbidden five grains.

Meat

• Apart from all animals having to be slaughtered in a kosher way, there is a list of animals whose meat can never be kosher. Any mammal which doesn't have cloven hooves and doesn't chew its cud, like a camel or pig, is non-kosher and forbidden during Passover. Shellfish, like lobsters, oysters, shrimp, clams and crabs, are also not allowed because they don't have fins and scales. The non-kosher label applies to any products that come from these animals.

Dairy

• Any type of dairy product which is made from non-kosher animals is also not kosher. Additionally, it's forbidden to eat dairy products with meat at any point during Passover. There is a prescribed amount of time that must pass between meat and dairy consumption, although this differs between countries. There is also a difference between how strictly kosher rules are applied to dairy products. For example, cheese is hardly ever considered kosher because it's hard to oversee its production and guarantee it is in fact kosher, while milk is usually commonly accepted even though it's also not very strictly monitored.

Grape Products

• While fruits, vegetables and all that is made out of them are generally accepted as kosher foods, grape products are a different story. Grape products like wine and grape juice are only kosher if they were produced by a Jew. Consequently, other juices may be considered non-kosher if they have been sweetened with grape juice. The same goes for baking powders, which are made with cream of tartar, a side-product of making wine.