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Fermented milk

Ingredients: milk
Taste: sharp and buttery flavor, stringy or ropy texture
Popular in: Finland, northern Europe
Time: 12-48 hours
Dominant microbes: Various Lactobacillus strains and Geotrichum candidum (yeast)
Tools: jar, coffee filter cover




Basic Viili

viili starter

coffee filter
rubber band

  1. Using 1 cup of pasteurized milk in a glass jar or cup, add 1 tbsp of viili starter or one packet of freeze-dried yogurt cultures (following the instuctions provided)
  2. Cover with a coffee filter or cloth, and tighten with a rubber band to prevent bugs from getting in, but allowing the yogurt surface to be exposed to air
  3. Let ferment at room temperature (70°-78°F)
  4. After 12 hours, check the texture of your viili (it should be thicker and slimy), after which the viili is ready. You can keep fermenting at room temperature for up to 48 hours
  5. Once the viili looks ready, place it in the fridge for at least 6 hours, after which it is ready to eat
  6. Add 1 tbsp of the newly made viili to fresh milk to continue the process, or store your starter for future use
viili starter
viili starter is either 1 tbsp of villi, or can be purchased as freeze-dried cultures

why pasteurized milk?
According to the 1939 Milk Ordinance and Code, pasteruization is “the process of heating every particle of milk to at least 143°F (61.7°C) and holding at such temperature for at least 30 minutes, or to at least 160°F (71.1°C) and holding at such temperature for at least 15 seconds, in approved and properly operated equipment” (PHS, 1940)

Pasteurizing milk creates an environment where the starter can thrive uncompeted, while raw milk would require the starter to compete for nutrients with other microbes already in the milk, making the fermentation process slower.

viili texture

Exopolysaccharides (EPS) give viili its characteristic ropy texture, mainly produced by Lactococcus lactis ssp. cremoris. Viili EPS are called viilian, which are phosphate-containing hetero polysaccharides. The structure can differ depending on the strain of L. lactis ssp. cremoris that produces the EPS, from repeating units of galactose, glucose, and rhamnose to homopolymers of galactose. More EPS is produced when glucose is a substrate (compared to high fructose substrate).

EPS production is not unique to viili

EPS are also produced by different microbes in in kefir, used to form the polysaccharide structure of the kefir grains; 
 however, the EPS produced in viili cannot auto-aggregate, thus cannot form grains. Instread, it is responsible for the ropy texture

viili microbiology

Mesophilic lactic acid-producing bacteria (LAB)
Lactococcus lactis subsp. lactis
lactic acid producing strain that contributes to the acidification

Lactococcus lactis subsp. cremoris
lactic acid producing strain necessary for the production of EPS, contributing to the ropy structure

L. lactis subsp. lactis biovar diacetylactis
lactic acid producing strain that contributes the aroma (buttery diacetyl)

Leuconostoc mesenteroides
lactic acid producing strain that contributes the aroma (buttery diacetyl)

from meso- meaning middle, and -philic, to love or like; mesophilic bacteria grow best from 20 to 45 °C (68 to 113 °F)
Consistency is produced by bacteria that produce exopolysaccharides
Geotrichum candidum
fungus that consumes lactate and contributes to flavor formation. It produces lipase and proteases that break down fats and proteins into fatty acids and peptides, creating the distinct viili flavors.

When villi is made commercially and sold in sealed cups, G. candidum will consume the oxygen in the cup and produce carbon dioxide, making commercial viili slightly carbonated. (Oberman and Libudzisz 1998)

Kluyveromyces marxianus
yeast that ferments lactose and galactose, and contributes to the yeasty flavor; key player in the formation of the ropy texture of the viili

Other fungal players
Saccharomyces unisporus

Oberman, H. and Libudzisz, Z. (1998) Fermented milks. In Microbiology of Fermented Foods ed. Wood, B.J.B. pp. 308–350, Vol. 1, 2nd edn, London: Blackie Academic & Professional.

additional resources 

Viili mini review
Bakry, A. M., and P. H. Campelo. "Mini-review on functional characteristics of viili and manufacturing process." J. Food Biotechnol. Res 2.7 (2018).

A brief history from the Nordic Recipe Archive
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