For the calcium solution: Combine both ingredients using a handheld blender to dissolve the calcium. Reserve refrigerated.
For the cherry jam: Boil the cherry purée, 80 percent of the sugar, and the calcium solution in a small sauce pot. In the meantime, combine the remaining sugar with the pectin to obtain an even mixture.
Add the pectin-sugar mixture to the jam by shearing it in with a handheld blender.
Return to a boil for 1 minute while stirring with a whisk.
Pour the hot jam into a half hotel pan to cool at room temperature.
Once it is cool, fill each of the 10 tubes with 30g/1.06oz of the jam. See Note below.
Close the tubes and reserve them at room temperature if using for that day’s service. If not, keep them refrigerated for up to 2 weeks.