Wash, peel and finely dice the quinces. Weigh 700 g of flesh. Mix in a large pot with approx. 1⁄4 l water and lemon juice. Bring to the boil covered and simmer for about 30 minutes. Let cool down in the pot.
Meanwhile skin, stone and finely dice the peaches. Add to the quinces with jam sugar. Bring to the boil while stirring constantly and cook thoroughly for at least 4 minutes until bubbly.
Immediately fill into prepared twist-off glasses (approx. 200 ml each). Close, turn upside down for approx. 5 minutes, turn over and let cool.