Color-enhanced SEM of a freeze-fractured kefir grain, showing bacteria in the interior. Kefir grains are a yeast/bacterial fermentation starter used to make kefir, a fermented milk beverage. Lactic acid bacteria produce lactic acid from the milk sugar - lactose. The acid coagulates the milk. Yeasts produce carbon dioxide and a low concentration of ethanol (alcohol). Kefir thus tastes somewhat like an acidic carbonated drink. Image width: 13.85 micrometers. Magnification: 7,220x if the image is printed 10 cm wide.