Start by washing and chopping the apples and cucumbers. You can leave the seeds in the apples since they will be strained out after blending. Remove the kale leaves from the stems and discard the stems.
Pour water into a high-speed blender, then add in the kale leaves, stuffing them down to create room. Add in the apples and cucumbers. The ingredients will likely come all the way to the top of the blender but will shrink down after blending.
Blend on high until all the ingredients are mixed and it resembles a liquid. Pulse or stop to mix in the ingredients with a spoon if needed.
Get a large bowl and place a fine mesh strainer over it. Pour the contents of the blender over the strainer so the bowl catches the liquid while the strainer keeps out the fiber and pulp. Use a rubber spatula to gently mix the pulp in the strainer to get out any excess juice. The pulp may be very foamy. Once the juice is strained, you can discard the pulp.
Squeeze the juice of half a lemon into the bowl of juice, and be careful not to get any lemon seeds in the juice. Pour the juice into a glass to enjoy as is, or store it in a mason jar in the refrigerator for up to 24 hours.
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Notes
You'll need a high-powered blender, like a Vitamix or Ninja blender, for this recipe. Other blenders may not adequately process all the high-fiber vegetables.
All of the unprocessed vegetables and fruits will take up a lot of room in the blender at first but then will shrink down a lot once they're blended. The capacity of the blender should be about 64 ounces in order to fit all the unprocessed ingredients.
You'll need a fine mesh strainer to make this green juice. You can also use a cheesecloth.
You can leave the seeds and core intact when you chop the apples since they will be strained out after blending.
For storage, keep this juice in an airtight container, like a mason jar, in the refrigerator. This fresh juice won't last long, so be sure to consume it within 24 hours.