Wash and clean the strawberries. Cut them into small pieces.
Put the strawberries in a large pot and fill with tap water. Cover with a lid and bring to a boil. Let the strawberries simmer for at least 15 minutes.
Get a large bowl ready and line a fine sieve with a muslin cloth. Pour the strawberry juice through the sieve and squeeze them really well in the cloth.
Mix citric acid and birch sugar and add them to the pot. Pour in the strawberry juice. Let the mixture boil and then simmer gently for 5 minutes. Taste the syrup and add more citric acid if necessary.
Fill the syrup into the prepared bottles with a funnel. Close the bottles and let them cool. Now you are ready to make your own strawberry syrup.