The phrase "to reserve the juice" means to save or keep a valuable or important part of something for later use or enjoyment.
Sentences with «to reserve the juice»
If you're really having trouble sourcing tomatoes, buy canned whole tomatoes (reserve the juice for the blender). (soupaddict.com)
Transfer turkey to a cutting board and let rest at least 30 minutes (internal temperature will climb to 165 °); reserve any juices in skillet. (bonappetit.com)
Combine reserved juice, cherries, 1 cup sugar and cornstarch in a 2 quart saucepan. (easydessert.org)