This fermented milk drink, originating in the North Caucasus Mountains of Eastern Europe, is sometimes known as effervescent milk. Due to the fermentation process of the kefir bacteria (where the natural products are carbon dioxide and alcohol) there may be a slight fizz to the milk, there may be a sound when you open the milk (almost like when you open a carbonated drink) or the bottle may feel firm. This is perfectly normal and no need for concern. The Kefir is made in open containers with a light covering so the alcohol can evaporate. Kefir is also fairly sour and can have a taste and aroma most commonly associated with sour dairy products – if you are not familiar with either Kefir or other cultured milk drinks (maas or buttermilk to the South African palate) this may alarm you, however it is also perfectly normal and no cause for concern.