How to Make Filmjölk at Home (And Why My Kids Prefer It to Kefir)

Filmjölk (also called Tykmælk in some countries) is a traditional mesophilic fermented milk that I started making in early 2026. If you've never tried it before, imagine something somewhere between drinking yogurt, sour cream, and milk kefir. My kids describe it as "drinkable sour cream".

Unlike ordinary yogurt, Filmjölk does not need to be kept warm while it ferments. It is a mesophilic culture, which means it can ferment at ordinary room temperature, making it remarkably simple to make at home.

The main thing you need is a live Filmjölk starter culture. Once you have an established culture, you can keep using a little from each batch to start the next one.

Filmjölk tastes surprisingly different from milk kefir, even though both are fermented from milk in a jar on my kitchen bench. I enjoy making both, but Filmjölk has become a favourite in our household because it is mild, smooth, and easy to make.

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Filmjölk is like drinkable sour cream

What is Filmjölk?

Filmjölk is a traditional Nordic fermented milk made using mesophilic lactic acid bacteria. Unlike regular yogurt, it does not need to be heated and incubated at a high temperature. It can simply ferment at room temperature.

I have never tried making regular yogurt or Greek yogurt. The idea of needing to heat the milk and then maintain a particular temperature has never appealed to me when there are simpler ways of fermenting milk at home.

Filmjölk is much more convenient. Add some live culture to milk, leave it in a jar on the bench, and wait for it to thicken.

It is also an heirloom culture. Once you have a healthy culture established, you can reserve some finished filmjölk and use it to inoculate the next batch rather than buying new starter every time.

What does Filmjölk taste like?

Filmjölk has a smooth, velvety texture and a mild but quite pleasant flavour. I find it noticeably more buttery and less sharp than milk kefir.

My kids describe it as "drinkable sour cream".  They love sour cream, and happily eat it by the spoonful, so their description shows how much they enjoy filmjölk.

Filmjölk can be reasonably thin and pourable, or it can become much thicker depending on how long it ferments. If I leave it fermenting for longer, I get something closer to Filbunke.

Some Filmjölk/Filbunke/Tykmælk I made at home

Filmjölk vs Milk Kefir

Filmjölk and milk kefir are both traditional fermented milk cultures. They are both made in a jar of milk sitting on my kitchen bench, but they produce quite different results.

Filmjölk is milder, smoother, and more custard like, while milk kefir is generally more tangy, acidic, and variable, and may develop a little carbonation depending on the season. Filmjölk is fermented with bacteria, while kefir grains contain a more complex community of bacteria and yeasts.

I enjoy both, but they have different uses in my kitchen. If you are interested, I wrote a blog post about the differences between them.

What is Filbunke?

Filbunke is closely related to Filmjölk, and when making it at home the distinction seems a little blurry. The same culture can produce something fairly pourable or something much thicker and spoonable depending on fermentation time and conditions.

For me, making Filbunke generally means leaving the Filmjölk to ferment for longer. The result is much thicker and closer to a custard or very thick yogurt than ordinary Filmjölk.

I am not particularly concerned about whether what I make would technically be classified as Filmjölk, Filbunke, or somewhere in between. For home fermentation, the important difference is mostly the final consistency.

Filbunke is thicker than Filmjölk

What you need to make Filmjölk

• Live Filmjölk starter culture
• Milk
• A clean glass jar
• Optional thermometer strip

You don't need a yogurt maker, incubator, expensive fermentation machine, or any special equipment.

I often use recycled jars because they're free, but a wide-mouth glass jar is much easier to clean and much more convenient if you're making Filmjölk regularly.

Where I got my Filmjölk starter culture

I started with a live heirloom Filmjölk culture rather than a freeze-dried packet. In my experience, the live culture established easily and has been simple to maintain. Once it was established, I could keep propagating it by saving some finished Filmjölk from each batch.

Live cultures can be difficult to post, however, so dried starter cultures are often easier to find. If you don't know anyone maintaining a live culture, a dedicated Filmjölk starter is probably the easiest way to begin.

This is the starter culture I would recommend for someone trying Filmjölk for the first time.

How to Make Filmjölk at Home

Compared with milk kefir and yogurt, there is surprisingly little information available about making traditional Filmjölk at home. I don't know if I am doing it "right" according to every traditional method, but I can tell you what I do and how it has worked for me.

I add some established Filmjölk starter to milk in a clean glass jar and leave it at room temperature until it thickens.

I usually use a simple screw-top lid. I prefer fermenting Filmjölk with the lid on because I have several other ferments in my kitchen and would rather minimise the chance of something else getting into the jar.

I normally leave it for around 24-48 hours, depending on the temperature and how active the culture is. If I want a thicker result, I leave it longer. Like many other traditional ferments, it doesn't need to be overly precise.

A simple thermometer strip can be useful if your kitchen temperature changes significantly through the year. You don't need one to make Filmjölk, but it can help explain why a batch takes longer in winter than it does in summer.

Once the Filmjölk has thickened, I put it in the refrigerator. I always save a little to start the next batch before I start to eat any.

Saving a little filmjölk starter for a new batch

How much starter should I use?

There are different recommendations for how much starter to use. When I first received my culture, I used a relatively large amount because I wanted to make sure the milk was well inoculated.

My first batch was roughly one quarter starter to three quarters milk. That was considerably more starter than many recipes recommend, I was deliberately being cautious with my first batch because I didn't yet know how active the culture was. It set quickly and developed the smooth, custard like texture I was hoping for.

Once a culture is established and working reliably, I don't think there is much need to obsess over exact measurements. The important thing is to use enough healthy starter to get the new batch fermenting reliably. 

Keeping the Filmjölk culture going

One of the things I like most about Filmjölk is that there are no grains to strain and maintain.

Each time I make a batch, I simply save a small amount of finished Filmjölk before eating or flavouring the rest. That saved portion becomes the starter for the next batch. I save a small amount from the finished batch before eating any.

The culture is kept in the refrigerator when I'm not actively making a batch. It continues to change slowly in the fridge, but fermentation is slowed compared with leaving it at room temperature.

Mine changes with the seasons, and with the temperature. That is normal for a living culture.

My experience making Filmjölk

I first obtained my Filmjölk starter as a liquid culture early in 2026 and wasn't entirely sure what to expect. There was much less information available than I was used to finding for kefir or yogurt.

When it arrived, it smelled a little like butter and a little like sour milk or kefir. It did not smell like rancid milk.

I was surprised by how quickly it established. After that first batch, I simply kept some aside each time and continued the cycle.

My kids like the taste because it is buttery and much more tame than kefir. With kefir they often add honey or other toppings, but they are happy to drink filmjölk without adding anything.

For me, filmjölk has also behaved more predictably than milk kefir. My kefir can vary noticeably from one batch to another, whereas my filmjölk batches tend to be quite similar.

Fermenting filmjölk turned out to be simpler than I expected. Sloshing a little live starter into milk every now and again is not particularly difficult, and the finished culture stores well in the refrigerator.

Filmjölk is not the same as kefir

What happens if you ferment Filmjölk for too long?

Once I had been making filmjölk for a while, I became curious about what would happen if I simply left a batch fermenting for much longer than normal.

My normal sweet spot is around 24 hours, but curiosity got the better of me and I once left one batch going for four weeks and documented what happened. 

Common mistakes when making Filmjölk

• Using too little healthy starter
• Fermenting somewhere that is unusually cold or hot
• Forgetting to save some finished filmjölk before eating the batch
• Mixing flavourings or fruit into the entire batch before reserving starter
• Expecting filmjölk to taste like yogurt
• Expecting every batch to set at exactly the same speed
• Confusing normal fermentation smells with spoiled milk

Filmjölk should develop a pleasantly acidic, cultured smell. If it develops mould, unusual colours, or an obviously rotten or spoiled smell, discard it rather than trying to rescue the culture.

Frequently Asked Questions

Where can I buy Filmjölk starter culture in Australia?

Filmjölk starter culture can be difficult to find in Australia. If you don't know someone maintaining a live culture, you can check current availability of starter cultures here.

What milk works best for Filmjölk?

I use A2 milk as that's what we use in our house. Full cream milk produces a richer result, while lower-fat milk produces a lighter texture. The culture can adapt to the milk you regularly use.

I would not use plant-based milk as a long-term substitute. Filmjölk is a dairy culture and is intended to ferment milk.

How long does Filmjölk take to ferment?

Mine generally takes around 24 hours to thicken, although temperature and culture strength, and room temperature make a difference. I often allow it longer when I want a thicker result.

Can I reuse Filmjölk to make more batches?

Yes. This is one of the main advantages of an established heirloom culture. Save a small amount of finished Filmjölk and use it to inoculate the next batch. 

Does Filmjölk keep fermenting in the refrigerator?

Yes, although much more slowly. I find that Filmjölk can continue to become thicker and more acidic while refrigerated, especially if it is kept for a long time.

Can Filmjölk become too sour?

Yes. The longer it ferments, the more acidic it becomes. I prefer mine relatively young, when it is smooth, mild, and buttery.

Can I make Filbunke from Filmjölk?

Yes. For me, the simplest way to make a thicker Filbunke style ferment is simply to leave the Filmjölk fermenting for longer until it reaches the consistency I want. 

Where to get Filmjölk starter culture in Australia

Filmjölk has quickly become one of my favourite fermented dairy cultures. It is simple to make, requires very little equipment, and produces a smooth, mild cultured milk that my family enjoys.

While I still make milk kefir regularly, Filmjölk has earned a permanent place in my kitchen and is one of the easiest heirloom cultures I have worked with.

Filmjölk is still relatively uncommon in Australia, and obtaining a live starter culture can be more difficult than finding kefir grains. If you want to start making it yourself, this is the starter culture I would recommend for first-time Filmjölk makers.

Once you have an established culture, however, you don't need to keep buying it. I simply save a little from each batch and use it to start the next one.

I mostly make Filmjölk for my family, but occasionally I have more starter culture than I need. When I have healthy cultures available to share, I may list them on my For Sale page, along with other things I have grown, propagated, or cultured.