Mustard powder has natural compounds that helps to emulsify the ingredients in high fat recipes. This means it makes the oils in the cheese become creamy instead of greasy when it melts, which is why dry mustard is the perfect addition to Macaroni and Cheese sauce. It also has a very subtle acidic flavor that gives a tangy balance to the rich and creamy dish without being noticeable, and the bright yellow color enhances the cheesy macaroni.