Working in batches, puree strawberries in a blender or food processor until smooth. Use a little of the lemon juice, if needed, to blend the strawberries.
Combine strawberry puree, lemon juice and sugar in a large Dutch oven, stirring until well mixed.
Heat the mixture to 190 degrees over medium-high heat, stirring occasionally. Do not boil. Remove from heat and skim off any foam.
Ladle hot concentrate into hot, sterilized pint jars leaving 1/4-inch headspace. Wipe rims and attach two-piece lids.
Process in a boiling water bath for 15 minutes. Makes 5 to 6 pint jars.
To Reconstitute: Mix one part concentrate with 3 parts water, seltzer or tonic water, or ginger ale.