Meanwhile, combine vinegar, sugar, 3 cups water, white peppercorns, and bay leaves in a medium pot. Bring to a boil, then set aside to cool.
Pour vinegar mixture over herring, cover with plastic wrap, and refrigerate for 3 days. While the herring can be eaten as is, it is common in Denmark to go one step further and flavor the fish with ingredients such as cloves or curry powder. Remove bay leaves before eating.