The soured juice (white borsch) for the zur should be prepared earlier. It is made the following way:
Scald 2 cups of whole-wheat flour with boiling water, pouring it enough to get a thin dough. When it cools, add 1 � pints lukewarm water and place a piece of whole wheat bread crust in it. Pour into a glass jar, tie with gauze and leave in warm place for three days.
Cook 1 � pints of vegetable stock with dried mushrooms and add � pint white borsch to the hot stock. Do not strain, as the soup should be slightly thick. If the zur is not sour enough, add some more white borsch. Add a crushed garlic clove along with 4 potatoes cut into cubes. When the potatoes are ready, salt to taste.