There will be slime

by Edith Salminen


Nordic people love fermented milks, with an average intake per person of 100g a day. We have in the Nordic region a distinctive subfamily of fermented milk and cream products sometimes referred to in English as the “ropy milks of Scandinavia”. These ropy milks are rather similar in flavour and acidity, but differ in consistency and mouthfeel. The Finnish one is called viili and it is a traditional fermented milk product involving lactic acid bacteria (LAB) that enjoy ambient temperatures between 17 and 22 °c, as well as a surface mould which makes the product unique in taste, aroma and appearance compared to all other Nordic fermented milks. The mould growing on the surface is Geotrichum candidum (the same mould which plays a crucial role in the development of certain cheeses). It feeds on the cream and forms a tasty, slightly fuzzy upper layer.

The slimy ropiness of viili is created by a specific strain of LAB called Lactococcus lactis subsp. cremoris. Other LAB strains used in industrially produced viili are Lactococcus lactis subsp. lactis biovar diacetylactis (contributes to flavour) and Leuconostoc mesenteroides subsp. cremoris. These LAB strains produce long chains of exopolysaccharides. Exopolysaccharides are long chains of many (‘poly’) sugars (‘saccharides’) that are excreted from the cell (‘exo’) as part of its metabolism. Other, more known exopolysaccharides commonly used in the food industry are Xantan and Gellan gum.

Viili was traditionally made in wooden barrels, often made of alder wood. Nowadays, one doesn’t need to carve a barrel of alder: making viili is a no-brainer. If you have full fat, good quality, unhomogenized cow’s milk, a 200ml plastic or glass jar and a viili seed you’re good to go. Go ahead and try it for yourself. Let there be slime!

Nordic people love their fermented milks, with an average intake per person of 100g a day. Finns and Danes rank highest in the bunch with a ravishing 41 kg per person per year (Fondén & et al. in Tamine 2007)! Yet what is perhaps less known is many people’s proclivity for a bit of slime in their fermented milk.

We have in the Nordic region a distinctive subfamily of fermented milk and cream products that Harold McGee refers to as the “ropy milks of Scandinavia” (McGee 2004, 50). These yoghurt-like substances are known under different names depending on their geographical origins: långfil in Sweden, tettemelk in Norway and viili in Finland. These ropy milks are rather similar in flavour and acidity, but differences in consistency and mouthfeel are noticeable even to a non-Nordic palate.

I am Finnish so viili is my bread and butter. Let me tell you a story of viili.


Viili is a traditional Finnish fermented milk product involving mesophilic bacteria[1]. In some scientific papers it has also been classified as a “mould-lactic fermentation product” (Tamine & Marshall in Law 1997). Viili is the modern version of old-school filbunke traditionally produced in Sweden, from where it made its way to Finland when the two countries were one roughly from the 12th century up to the year 1809 (Fondén & et al. in Tamine 2007). It is hard to say how long viili has existed, but there are records of it being produced and consumed in Finland since the 19th century. Somewhere along the way, distinct from its Swedish ancestor, viili gained a mould growth on the surface, which makes it unique in taste, aroma and appearance compared to all other Nordic fermented milks (Law 1997). Beautiful, delicious surface mould.

Today, viili is mostly considered as breakfast or a snack, whereas back in the days it was regarded as a full meal, especially in summertime (Linquist 2009, 79). Nowadays viili is most often consumed topped with sugar and cinnamon, or served with fruit. To give viili a modernising face-lift, fruit-flavoured and -coloured industrial viili called Viilis was introduced to the market in the 1980s and continues to be popular among children (Tamine & Robinson 1988).

The reason why I decided to get to know my beloved slimy friend more deeply is because I have been taking it for granted all these years. Available in any little kiosk or food store in Finland, viili is no longer an artisan product as it used to, the viili seed passing from mother to daughter. I want to change that.

Once upon a time…

The first commercially sold viili was produced in a sauna hut by a riverbank close to the town of Sipoo in South-eastern Finland in 1929 (Ingman 2013; Wallén 2003). A young man called Hjalmar Ingman made his first trip to Helsinki to sell his viili – thirty 1-liter wooden jars of it to be exact – on June 23rd of that year. Safe to say his efforts paid off. Ingman’s viili was a succulent success. Except for a brief halt in business from spring to October 1941 due to WWII, Ingman’s viili business kept growing. In 1960, he founded Hj. Ingman Ky, a public organization owned by a group of municipalities. That is also when his viili would become available in the first milk shops such as Wickström, HOK and other Finnish supermarkets (Wallén 2003, 220).

Determined and young Mr. Ingman (Wallén 2004).

As mentioned above, viili was traditionally made in wooden barrels. According to old sources, the best wood to use was alder wood. Whether the wood added some important aromas or flavour to the final product or had some other particular function is uncertain, but one could guess it did. When time to eat, the viili barrels (hence the Swedish name filbunke, or ‘viili bowl/barrel’) were placed in the middle of the table for shared consumption. The unwritten eating rules were common knowledge: one should always keep to one’s own corner of the barrel and one was never to only skim the creamy surface that for many was the most delicious part. From the 1920s onward the wooden barrels were gradually replaced by single serving glass jars (Lindquist 2009, 78). Nowadays, viili is sold in plastic single-portion-sized (250g) containers sealed with an aluminium foil cap.

It’s all in the slime

What is so precious and exciting about viili is its distinctive ropy and gelatinous consistency, which gives it its characteristic mouthfeel. Other Nordic fermented milk products with mesophilic bacteria have this to some degree, but viili is downright the slimiest I’ve encountered. Slurp a spoonful of viili and you can feel how it holds together firmly but softly. In fact, viili is so cohesive that if some of the viili spills out from its container the rest of it will most probably be dragged out of the container too. It’s like a dairy slinky. As a kid I remember thoroughly enjoying and playing with this feature.

Ropy viili.

The slimy ropiness is created by a specific strain of lactic acid bacteria (LAB) called Lactococcus lactis subsp. cremoris. Other LAB strains used in industrially-produced viili are Lactococcus lactis subsp. lactis biovar diacetylactis (contributes to flavour) and Leuconostoc mesenteroides subsp. cremoris (Meriläinen 1984). These LAB strains produce long chains of exopolysaccharides at the correct fermentation temperature to create the characteristic consistency and also contribute to the aroma and flavor profile of viili (Kahala & Joutsjoki 2012, 177).

Exopolysaccharides are long chains of many (‘poly’) sugars (‘saccharides’) that are excreted from the cell (‘exo’) as part of its metabolism. They have multiple applications in various food industries, as their properties are almost identical to different plant and algal gums currently in use (e.g. xantan gum, gellan etc.). In general, the various exopolysaccharides are increasingly used to attain certain wanted textures and consistency as well as to improve physical stability in food items (Giavasis & Bilideris 2007). To give you a concrete and more familiar example, Gellan gum (E number E418) forms soft, elastic, transparent and flexible gels, but forms hard, non-elastic brittle gels once de-acylated. Xanthan gum (E number E415), another common exopolysaccharide and often used in gluten-free baked goods, hydrates rapidly in cold water without lumping to give a reliable viscosity, encouraging its use as thickener, stabilizer, emulsifier and foaming agent.

[1] Gellan gum molecule. Source: Water Structure and Science, Martin Chaplin, 2012.
[2] Xantan gum molecule. Source: Water Structure and Science, Martin Chaplin, 2012.

Moreover, the naturally-occurring exopolysaccharides that give rise to sliminess also prevent syneresis (the expulsion of water from a gel) and graininess, resulting in a pleasant natural thickness in the product (Macura & Townsley 1983). According to Sundman, It is thanks to these exopolysaccharides that the Nordic ropy fermented milks, and viili in particular, keep longer than many other fermented milk products under the same conditions (Sundman 1953). 

[3] Lactococcus lactis subsp. cremoris, bar: 1 µm. Photo by Bart Weimer, Utah State University.

Certain LAB strains, but also yeast and fungi, excrete exopolysaccharides as part of their metabolism. Research shows that these molecules have beneficial effects to human health, being antitumorous, immunostimulatory, hypocholesterolic and hypoglycemic (Giavasis & Bilideris 2007.) The exopolysaccharides do not interact directly with the pathogenic agent, but they do stimulate the immune system to respond and are therefore referred to as “biological response modifiers” (Giavasis & Bilideris 2007).

(For more on lactic acid fermentation, read this article on the blog and listen to this podcast of one of our talks for noma stagiaires and staff.)

Delicious mould

Often, moulds and fungi tend to not tolerate lactic acid bacteria very well, that is why you rarely find, for example, green mould on your yoghurt (unless its very old) (Frisvad 2014, personal communication). But what distinguishes viili from its other Nordic counterparts is in fact its delicate mouldy surface. When making viili, the milk cream rises to the surface (a normal occurrence when unhomogenized milk is left to stand). Many Finns consider this upper layer the most delicious part of viili, as do many of us at the lab. This deliciousness is not only because it is composed of cream (duh) – the mould Geotrichum candidum (which plays a crucial role in the development of certain cheeses, particularly small-format goat’s cheeses from the Loire Valley) feeds on the cream and forms a tasty, slightly fuzzy upper layer (Kurmann et al. 1992). 

[4] Geotrichtum candidum x1000 LPCB stain. Photo by George Barron 2013. 

The G. candidum also contributes to viili’s overall flavour formation giving it some fruity and mushroomy notes. Like most other moulds, G. candidum is aerobic and therefore only develops on the surface of the viili (Frisvad 2014 personal communication). This mould also consumes lactate (any salt or ester of lactic acid). This process lowers the acidity in viili resulting in a mild and delicate, slightly acidified milk flavour – less acidic than the similar Swedish långfil, for example. As moulds consume oxygen and produce carbon dioxide, an airtight viili jar bought from the store can be slightly carbonated when opened – totally fine, and totally tasty (Kahala et al. 2008,105). Some of this carbonation could also be due to heterofermentative LAB. In addition to G. candidum, traditional viili also contains the yeast strains Kluyveromyces marxianus[2] and Pichia fermentans. In industrially-produced viili, however, these two yeast strains are considered contaminants.

All for slime and slime for all

Making viili is a no-brainer. If you have full fat, good quality, unhomogenized cow’s milk, a 200ml plastic or glass jar and a viili seed you’re good to go (unless you happen to be located in a very warm climate). When in Finland, one can walk into practically any little food store or kiosk and find viili next to milk, butter and yoghurt. In Denmark on the other hand, viili is nowhere to be found, but that’s what kind mothers are for. A quick call to Finland and I had both a viili seed and my mother in Copenhagen a week later. That’s what I call a special delivery.

But do not worry, fellow viili-lover – there is another way to get your viili going if you don’t happen to have a mother in Finland. To my delightful surprise while reading Sandor Katz, I discovered that a viili seed, a real traditional one, was transported dried in a piece of cloth to the United States over a 100 years ago. The family with Finnish origins, now American, run a webstore called GEM Cultures selling various microbial cultures that have been in their family for ages, and among them a viili culture. Similar online stores selling viili seeds are Happy Herbalist, Cultures for Health, and Yemoos Nourishing Cultures. I tried the latter, just out of curiosity and because they send you the seed dried. I also discovered a woman from Norway named Eva Bakkeslett, an artist and cultivator who as a part of her artistic work uncovers forgotten or rejected practices, concepts and cultures which she then cultivates and shares with others. Eva has made a whole anthropological art project on my beloved slimy milk! Check out her work here.

It never ceases to amaze me when, concentrating on one single esoteric subject, one finds leads and connections all over the world. We often become so used to our distinctive cultural food items that we forget their peculiarity and their beauty. Stumbling upon these viili lovers all the way in the United States really made me appreciate this odd Finnish dairy product even more.

This is not a drill.

As we speak, there are containers of different sizes all over the lab breeding slimy deliciousness. Though I have to admit that stepping outside of my culturally constructed box when it comes to viili has been challenging. What to do and what to create with something that is already so good and special as it is? How to give a new angle to it without losing its essential character? Luckily this is what we do here at the lab and I’ve got a great team pushing me to rethink viili and all its potential. The full results of my viili experiments remain to be seen, but what I know without a doubt is that I have an important mission to spread the seed. Getting the sporadic visitors and curious passers-by to take home a few tablespoons of viili is my immediate aim. So far viili seeds have travelled to Norway, Austria, Greece and back home to Finland. Slowly but surely, my humble Finnish ropy milk will take the world over. There will be slime –

to be continued…


[1] Mesophilic bacteria are medium temperature bacteria, a group that grow and thrive in a moderate temperature range between 20°C and 45°C. The optimum temperature range for these bacteria in anaerobic digestion is 30°C to 38°C.

[2] This yeast is also produced commercially as a nutritional and bonding agent for fodder and pet food, and as a source of ribonucleic acid in pharmaceuticals.


[1] (Accessed March 24th 2014).

[2] (Accessed March 24th 2014).

[3] (Accessed March 18th 2014).

[4] (Accessed march 18th 2014).


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Frisvad, Jens Christian, personal communication at the Lab on March 12th 2014.

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Sundman V. “On the protein character of a slime produced by Streptococcus cremoris in Finnish ropy sour milk”, Acta Chem. Scand., vol 7, 1953: 558-560.

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Wallén, B  Juusto-Uusimaa: Itä-Uudenmaan kadonnut juustonvalmistusperinne/Ostnyland : Den försvunna osttillverkartraditionen i Östra Nyland, ETC-consulting, Finland, 2004.