Viili (filbunke in Swedish, or simply fil) is a kind of yoghurt (a mesophilic fermented milk) found in Finland that originated in Scandinavia. This cultured milk beverage is the results of microbial action of lactic acid bacteria (LAB) and a surface-growing yeast-like fungus Geotrichum candidum present in milk, which forms a velvet-like surface on viili. In addition, most traditional viili cultures also contain yeast strains such as Kluveromyces marxianus and Pichia fermentans. The LAB identified in viili including Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis biovar. diacetylactis, Leuconostoc mesenteroides subsp. cremoris. Among those mesophilic LAB strains, the slime-forming Lc. lactis subsp. cremoris produce a phosphate-containing heteropolysaccharide, named viilian. Viilian is similar to kefiran produced by kefir grains. The production of exopolysaccharides (EPS) by the strain forms the consistency character of viili and it has been claimed to have various functional benefits toward the rheological properties of milk products and the health improving potential.
Several variants of fermented milk products are found in Western Finland and Sweden, such as filmjölk or långfil, which vary in consistency and fermentation. In Norway, filmjölk is usually named "kulturmelk" or "surmelk", while in Gotland and Iceland, the name "skyr" is used to refer to fermented yoghurt variants.
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