prostokvasha

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A thick soured milk product, similar to unsweetened yogurt but less sour or kefir but thicker. In Russia or other former USSR republics, commercial and home-made prostokvasha comes in different varieties, as "varenets" (варене́ц), "ryazhenka" (ря́женка), katyk/qatıq (каты́к), etc.