Schmaltz herring is a fatty herring cured in salt and pickled in a brine sweetened with brown sugar. Despite some claims to the contrary, schmaltz -- a Yiddish term for rendered chicken fat -- is not used in the preparation of schmaltz herring; the term simply refers to the high fat content of the fish. Ask the seafood vendor for mature, late-season herring when preparing to make this dish.
Place a thin layer of kosher salt in a rectangular glass dish with either no or low side walls. Place the herring skin-side-up on the salt. Cover with remaining salt.
Cover the dish with cling film. Place a heavy pan or skillet over the wrap to press the salt into the fish.
Refrigerate the herring for 2 to 3 days. You do not need to turn the herring or add salt.
Remove the herring from the salt and rinse in water. Soak the herring in fresh water for 2 to 3 hours.
Place the onion, mace, bay leaf, cloves, allspice, salt, peppercorns, brown sugar, water and wine vinegar in a saucepan and bring to a boil. Simmer for 5 minutes.
Remove the herring from the water and place them in the glass jar.
Pour the hot liquid over the herring in the glass jar and allow to cool before covering.
Refrigerate at least three days before serving.
Some people prefer to cut the herring into bite-size pieces before placing it in the glass jar. Removing the skin at this point is an option, too. The salting process kills much of the bacteria in the fish, and the vinegar in the pickling solution does the rest of the job. It also softens any remaining bones in the fish. Schmaltz herring preserved in this way will keep in the refrigerator for up to five months.
Always use at least a 50-percent vinegar solution to pickle herring. Lower amounts may allow the development of bacteria, particularly botulism. Always keep the pickled herring refrigerated as an added safety precaution. Use heavy glass canning jars for the pickling and storage steps; thinner glass jars may crack when hot liquid is poured into them.