Measuring: I measure the grapes in dry measuring cups first, before dumping them into my blender – I find that the grapes absolutely DON'T measure out the same way once they're in the blender, due to the fact that the blender's measurement marks are geared to measuring liquids. (For example – 2½ cups of grapes, once dumped into my blender, actually measures in the blender as 3½ cups – a big difference!)
Quantities: As I mentioned in the post, popsicle molds with six 3-ounce compartments seem to be the most prevalent (although the molds I own, which you see in my photos, are Norpro's highly-rated 10-pop molds). So I wrote this recipe for that amount. If your mold has four 3-ounce compartments, start with 2 cups of grapes (measured in dry measuring cups). Alternately, if your mold has eight 3-ounce compartments, start with 4 cups of grapes.
Varieties: Any seedless table grape will work for this recipe, but the quality, sweetness and flavor of the grapes you start with will have a big impact on how your grape popsicles taste once frozen. Green grapes tend to be a little less sweet, for example. Regardless of the variety, always choose good grapes – ones that are fresh and really flavorful.
To make striped popsicles: To make six 3-ounce pops, you need to begin with 2½ cups of grapes, in whatever proportions or colors you choose. For the two-color pops pictured in this post, I started with 1¼ cups of green grapes and 1¼ cups of red. Blend each type of grape separately, and then carefully spoon each type of grape into your popsicle molds in 3-5 stripes, layering one on top of the other and gently pressing down on the grapes as you layer them so there are no air pockets to prevent the pops from holding together. Once you've spooned all the grapes into the molds, pour the remaining juice evenly over the pops, noting however, that you may choose not to use darker juice from red or black grapes, as that may slightly discolor lighter layers of green grapes
Long-term storage: Once your pops are frozen, if you want to remove them from the molds (so, for example, you can use the molds to make more pops!), the best way to store your pops is individually wrapped in plastic, and then stored together in a large freezer bag.