Wash, clean and cut the strawberries into pieces. Mix with the jam sugar. Wash the untreated orange, grate dry and peel the peel in zests. Squeeze all oranges and measure 1/2 litre juice.
Pour into the strawberries, stir and bring to the boil while stirring. Cook for 3-4 minutes until bubbly. Fold in the zest and vinegar. Pour the jam into the prepared twist-off jars, place them on the lid for 5 minutes, turn them over again and let them cool down.