Milk kefir is a fermented dairy product that's similar to yogurt but in a drinkable form, and it actually has a much higher level of healthy probiotics. It's just as good when added to smoothies, as here, where it is combined with kiwi, apple, and fresh mint leaves. If you have a hand (or immersion) blender, you can use that to blend the drink. Otherwise just combine everything in a regular blender.