To remove mustard stains, first rinse in cold water. Then you can either wash the item in cold water while rubbing with laundry bar soap or rub a liquid enzyme detergent into the stain and allow it to sit for a few minutes. Soak 12 hours in soapy water. If necessary, you can try a bleach solution on white garments. Glycerin applied to the stains and allowed to sit for about an hour may remove stubborn mustard stains.