Based upon Chris Banker's talk at NHC 2013. Procedures here.
Adding a blend of tart cherry juice and black cherry juice at kegging. Carbonate to
Ferment as usual. FG should in the 0.098 range for fully fermented cider.
At kegging, add the stabilizing agents (campden and potassium sorbate), cherry juices, and apple juice to backsweeten.
This recipe uses fresh-pressed cider juice. Acids and tannins will be present. If using store-bought apple juice, measure pH - should be in the 3.6 to 4.2 range, targeting 3.0-3.8. If reading is above 3.8, adding malic acid will help to acidify the solution. Add at 1 tsp per gallon according to taste. See this article for how to precisely adjust to taste with acid and tannins.
Target 2.7 volumes of CO2. For a CO2 saturation volume of 2.7 at 42° F, 15.5 PSI will be needed.