(), also known as , is a traditional fermented milk product from Sweden, and a common dairy product within the Nordic countries. It is made by fermenting cow's milk with a variety of bacteria from the species Lactococcus lactis and Leuconostoc mesenteroides. The bacteria metabolize lactose, the sugar naturally found in milk, into lactic acid, which means people who are lactose intolerant can tolerate it better than other dairy products. The acid gives a sour taste and causes proteins in the milk, mainly casein, to coagulate, thus thickening the final product. The bacteria also produce a limited amount of diacetyl, a compound with a buttery flavor, which gives its characteristic taste. has a mild and slightly acidic taste. It has a shelf-life of around 10–14 days at refrigeration temperature. Overview In the Nordic countries, is often eaten with breakfast cereal, muesli or crushed crisp bread on top. Some people add sugar, jam, apple sauce, cinnamon, ginger, fruits, or berries for extra flavor. In Norwegian it is called () ('sour milk') but the official name is (). The drink is also popular in Latvian kitchens, where it is called , ('fermented milk' or 'sour milk') and can be bought ready from stores but is more commonly made at home. It can also be purchased and is popular in the neighboring country, Lithuania, where it is called or ('sour/fermented milk'). Due to its popularity, it can be bought in many stores alongside kefir. Manufactured is made from pasteurised, homogenised, and standardised cow's milk. Although homemade has been around for a long time (written records from the 18th century speak of -like products, but it has probably been around since the Viking Age or longer), it was first introduced to the Swedish market as a consumer product in 1931 by the Swedish dairy cooperative Arla. The first was unflavoured and contained 3% milkfat. Since the 1960s, different varieties of unflavoured have been marketed in Swedish grocery stores. , a more elastic variant of was introduced in 1965; lättfil, with 0.5% milkfat was introduced in 1967; and , with 1.5% milkfat, was introduced in 1990. In 1997, Arla introduced its first flavoured : strawberry-flavoured . The flavoured was so popular that different flavours soon followed. By 2001, almost one third of the sold in Sweden was flavoured . Since 2007, variations of include with various fat content, flavoured with fruit, vanilla, or honey, as