Japanese mustard refers to oriental (yellow) mustard and is a condiment with a strong spiciness. It is used for cooking Japanese and Chinese food. Western style mustard refers to white mustard, which has a more subtle flavor and fragrance and is not as spicy. It is used for sandwiches and sausages. Whole grain mustard is made by mixing white mustard with black mustard seeds and used for things like flavoring vinegar. Sushi chefs use Japanese mustard to offset the greasiness of fatty fish such as bonito and tuna.