Yogurt + tahini = paste?

Question

I had dip made with Target store brand plain nonfat Greek yogurt, minced garlic, powdered ginger, lemongrass paste, salt, and nothing else; the dip was soft and creamy. I added some Sprouts store brand tahini, which is VERY runny, about the consistency of soy milk, with about a 2 to 1 ratio of dip to tahini. You'd assume that adding liquid to a creamy dip would make it thinner… but instead, it became dense, sort of stiff, and very sticky! Can anyone explain what happened here?

Answer 1

Adding a small amount of water to tahini causes it to thicken into a paste because of carbohydrate binding. Clearly, the yogurt had just that amount of water. The solution to getting it to thin out again is to continue adding water or other liquid until it "unbinds", just as you do for tahini sauce.