The strawberries need to be thoroughly cleaned and washed with water, in which you've dissolved the tartaric acid (1 1/3 tbsp (20 g) tartaric acid for every 4 1/5 cups (1 liter) of water).
Add the sugar and water to the strawberries and boil initially on low, then on high temperature, to the desired consistency of the syrup. Be sure to constantly remove the foam.
Several minutes before removing from the heat, add the tartaric acid. Leave the jam to cool and pour it into jars.