Koop's™ Mustard Stone Ground. Since 1897. Gluten free. Full rich flavor and robust texture in a classic stone ground mustard. Net Wt. 12 oz (340 g). In 1897, a young adventurer named Peter Koops set out from Holland to create his own American dream. He began with a simple hand-crank mill and the finest ingredients to produce robust, stone-ground mustards sold by the ladle from his horse-drawn cart. Our delivery methods may have changed, but our attention to quality and freshness remain the same. Certified Gluten-free. Visit www.koopsmustard.com.