What is
Yogurt, in simple terms, is the bacterial fermentation of milk which is often sweetened or flavored. Lactobacillus & Streptococcus are the vital bacteria's for the yogurt's thick texture and consistency.
Quark is a type of fresh dairy product, common for the cuisines of German-speaking countries made by warming soured milk until the desired degree of coagulation (denaturation, curdling) of milk proteins is met, and then strained.