How to keep a green smoothie from getting 'frothy'?

I don't know how to solve it once it's happened, but it's caused by the high speed of your blender. I use an Oster blender and never have froth in my green smoothies, so maybe trying a different blender will prevent it. If you juice greens they get frothy, so it's not the fibre NOT breaking down - maybe the opposite. Pulsing the blender a few times at the end might get rid of some of the froth. I always pulse a few times at the end to get some of the incorporated air out of my smoothies. High speed blenders incorporate a lot more air than my blender does, though. Not sure if that'll cut it for you.

As Catohound already mentioned, it's a symptom of using a high speed blender. You may find this technique useful.

Tcrn the blender to its lowest setting and then slowly ramp it up until the top of the liquid just starts to circulate (usually around speed 4 or 5 on a Vitamix). As you run it at this low speed, you will see bubbles coming out in the center.

My wife and I do this with our Vitamix and it generally gives good results.

Add a tablespoon or two of chia seeds - they magically eliminate the froth.

Two major sources of foam are (1) air whipped into bubbles, and (2) insoluble fiber.

To help with #1, after blending everything the way you normally do, turn the blender to a lower speed setting for a few seconds to allow bubbles to coalesce and burst. Article with video.

For problem #2, you can

• Reduce the sources of insoluble fiber (leaves, peels, apples)

• Add some soluble fiber sources for a creamier mouthfeel (bananas, mangoes)

• Add some oil to pop some of the bubbles. Ideally a healthful oil such as flaxseed oil or coconut oil, but if you don't want to impart any flavor regular neutral cooking oil will work. DO NOT use extra virgin olive oil because it will turn very bitter in a blender.

This article goes into more detail.

After blending, turn the mixer to low and add a few drops of canola oil. It will knock out the froth and replace it with a more "liquidy" product.