If you are making a recipe that calls for whole grain mustard and you don't have any in the cupboard, then you need to find a substitute in a hurry. Additionally, if someone you know is not fond of the mustard taste, then you might need to find a condiment that still has the heat mustard offers, without using actual mustard.
Stone ground and celery seeds
Stone ground mustard is not quite dry mustard, and it is not quite whole grain mustard. This is because the stone ground process partially grinds the mustard seeds. So you end up with some of the texture of whole grain mustard, while still maintaining the mustard flavour. Adding celery seeds to the stone ground mustard will give the stone ground mustard more of a whole grain mustard texture while not affecting the flavour. This is because the celery seeds are whole like whole grain mustard seeds. Simply add celery seeds until the textures is to your liking.
Horseradish is a root vegetable that contains an immense amount of heat. After harvesting, it is often combined with vinegar and other spices to temper the heat. If you want the bite or heat of whole grain mustard without actually having the mustard, try grated horseradish available in your supermarket's condiment aisle. There are also other "creamy" varieties that are more like a sandwich spread that you can try for the same effect.
If you are looking to retain the heat of mustard, without the actual whole grain mustard seed, then try a wasabi sauce. It can be simply made by adding 10 ml (2 tsp) of wasabi powder to 15 ml (1 tbsp) of water. Allow that to sit for 10 minutes so that the water and wasabi really mix well. Then add that mixture to 125 ml (1/2 cup) of mayonnaise. Stir until well mixed. You can then spread it on sandwiches or meats in place of whole grain mustard.
There are many different varieties of mustard on the market that are made throughout the world. If you do not like the texture of whole grain mustard, then try switching to a smooth or stone ground mustard. If the heat of the mustard is your issue, then try varieties that add sweeteners like honey, sugar or maple syrup. There are also exotic mustards such as cranberry or even beer mustard. Try substituting one of these items into your recipe based on the flavour profile you are seeking.