At the heart of every spreadable mustard are ground mustard seeds, which provide the condiment’s characteristic bite and aroma. The seeds themselves are used around the world as a seasoning in their own right, adding a unique, nutty flavor you might not immediately recognize as mustard. In the Bengali region of India, for example, black mustard seeds are a common flavoring for fish, and in other parts of India, mustard seeds are a common flavoring for yogurt-based sauces, rice, and curries. A common technique for showcasing the flavor of mustard seeds is to lightly fry the seeds along with a handful of curry leaves in oil, then fold this aromatic oil into rice or yogurt or toss it into cooked dishes.
Mustard seeds are also used in other cuisines and make regular appearances in familiar dishes such as pickles, where they’re added to the pickling brine, as well as cured meats such as corned beef, where mustard seeds (along with coriander seeds, juniper berries, and black pepper) are used in the curing process. They can also be enjoyed as a condiment on their own — simmered in a mixture of vinegar, water, and brown sugar, they become pickled mustard seeds or mustard caviar, a vibrant, close cousin of grainy mustard that makes for a refreshing changeup from regular mustard.
Mustard oil is an often-overlooked flavoring, but if you have an adventurous palate, it’s worth seeking out. Popular in many Asian cuisines (it’s a signature flavor in the cooking of West Bengal in India as well as in Pakistan and Bangladesh), it has a distinctive bite reminiscent of wasabi that’s even more intense when the oil is heated. It can be used in a number of ways — as a flavoring in pickling brines, as a frying medium, and as a flavor accent for salad dressings and other dishes.
Enticing as mustard oil may be, it’s never become a popular condiment in the U.S.
If you venture into an Indian specialty market and find mustard oil, every single bottle will be labeled “for external use only.” This is because mustard oil contains high levels of erucic acid, a fatty acid (also found in related plants such as kale) that was found in animal-based experiments in the 1950s to be associated with heart disease. Out of an abundance of caution, the U.S. banned mustard oil for human consumption. It’s worth noting, however, that more recent human-based studies on the effects of erucic acid have been inconclusive, and Asian diners have been cooking with and enjoying mustard oil with no apparent ill effect for centuries.