Milk kefir is a probiotic drink that can be found next to yogurt and other dairy products in the refrigerator case of supermarkets and health food stores. Be sure to buy the unsweetened variety for this recipe, since you add fructose. Strawberries are pureed with the kefir for a quick and easy smoothie, and a fresher tasting alternative to the pre-flavored bottles of kefir. Mint makes a lovely garnish, as would basil.