Rai pickle, also known as rai mirchi pickle, is a flavorful and spicy pickle made from mustard seeds and chili peppers. It's typically made by combining mustard seeds with chili peppers and a blend of spices such as fenugreek seeds and asafoetida (hing) and allowing the mixture to pickle in oil for several days or weeks. Mustard kernels, also known as Rai dal, are the main ingredient in making pickles.