In a larger saucepan, make a stock of water, vinegar, the peeled onions, bay leaves, mustard seeds, peppercorns, juniper berries, salt and sugar. Cook the meat in the broth for about 2 hours until it is cooked through. Then take it out of the pot and cut into larger pieces.
Pour the brew through a sieve and pour it back into the pot. Add the meat again and let it steep for a few minutes at a low temperature. Remove the pieces of meat with a slotted spoon and place in an appropriately sized bowl.
Stir the instant gelatine into the stock with a whisk. Then pour the stock over the meat until it is well covered. Then let it cool down.
After a day in the refrigerator, the sour meat is ready to be eaten.
It is best eaten with fried potatoes or black bread.