Filmjölk (“fil”) is Sweden’s everyday fermented milk: mild, slightly thick and gently sour, eaten from a bowl with muesli or cereal, or with jam. Unlike yogurt, it sets at ordinary room temperature, because it’s made by mesophilic lactic acid bacteria – mainly Lactococcus lactis and aroma-producing Leuconostoc – rather than the heat-loving cultures of yogurt. That makes it one of the easiest fermented milks to keep going at home: a few spoonfuls of the last batch in fresh milk, a day on the counter, done.
Filmjölk, Långfil and the Butterwort Story
Scandinavia has several related fermented milks. Långfil (Sweden), tettemelk (Norway) and Finland’s viili are “ropy”: they stretch into strings because some strains of Lactococcus lactis subsp. cremoris produce exopolysaccharides. Norwegian folklore says leaves of the carnivorous plant butterwort (Pinguicula vulgaris) were added to milk to start tettemelk – and when researchers sequenced the microbes on butterwort leaves from five rural Norwegian sites, every sample carried Lactococcus, along with the genes for making those ropy exopolysaccharides (Porcellato et al., 2016). Ordinary filmjölk is the non-ropy cousin.
What’s in Filmjölk
The Swedish Food Agency lists vitamin D–fortified 3% filmjölk at 57 kcal, 3.3 g protein, 2.8 g fat, 4.6 g carbohydrate, 114 mg calcium and 1.0 µg vitamin D per 100 g (Livsmedelsverket) – close to milk, with some of the milk sugar used up by the bacteria. Homemade filmjölk contains live cultures. The European Food Safety Authority accepts that live yogurt cultures help digest lactose (EFSA, 2010); filmjölk’s cultures are different, but many people who find milk hard to digest do well with fermented milks.
Making It Safely
Use pasteurized milk: raw milk can carry harmful bacteria, and fermentation doesn’t reliably make it safe (CDC). Start with a few spoonfuls of plain filmjölk from the shop, or a freeze-dried filmjölk/mesophilic starter, and leave it at about 18–24°C until it sets (recipe card below). If a batch hasn’t set within about 24–30 hours, or turns pink, slimy in the wrong way, moldy or foul-smelling, discard it and start again from fresh culture.
Other room-temperature fermented milks on the site: South Africa’s amasi and Morocco’s raib. For a fermented milk with yeasts as well as bacteria, see kefir. The same kind of room-temperature culture makes cultured buttermilk, sour cream and crème fraîche.