I went there 3 times last week, and each time, i was very careful to figure out what they have in it. After all, Pinkberry is from Korea, Japanese and Koreans eat somewhat similar things, especially snack wise, we have a lot of stuff in common. So I thought about what this sour/sweet flavor is all about. I googled everywhere, and some blog site said to use Yakult.
[Here is wikipedia info on Yakult for those who are not familiar with it]
"Yakult is a Japanese probiotic yogurt-like product made by fermenting a mixture of skimmed milk with a special strain of the bacteria Lactobacillus casei Shirota. It was created by Minoru Shirota who graduated from the Medical School of Kyoto University in 1930. In 1935, he started manufacturing and selling Yakult. Official claims state that the name is derived from jahurto, an older form of jogurto, the Esperanto word for "yogurt"."
It definitely has that tangy yet sweet, and yogurt-ish flavor. Although regular frozen yogurt recipe calls for strained Greek style yogurt such as Fage, it's too creamy. Pinkberry stuff has A LOT of water in it, that's why it's so refreshing. All the Japanese ice cream use less fat, and that's why it's lighter.
Enough bullshit, and here is the recipe, and trust me, it is damn good.
1 pint of fat free plain yogurt -strained
3 yakult (each is about 2 oz)
2 tablespoon of sugar
After straining the yogurt (it renders a lot of water, and since we are adding liquid (Yakult), it's important to strain yogurt first), mix it with Yakult and sugar, put them into ice cream maker, and churn it for about 20 minutes.
As Aya Orangeoilgwa says, it gets way too firm once you freeze the mixture (due to high water content), so the key is to eat either right away, or thaw it pretty good before you eat them.
Due to the lawsuit against Pinkberry, we might get the exact recipe soon, but until then, this recipe will do the magic. I am making a batch tonight using Bikkle (similar to Yakult). I will report the result soon.