If you’ve spent any time at all on a general fermented foods forum, you will know the huge variety of cultures that are out there.
If you’re looking for fermented vegetable recipes, you’ll be hearing about saurkraut, kimchi, cortido, kvass, dill pickles. If you want something fizzy to drink, there’s kombucha, jun, and water kefir.
If you want a dairy ferment, there’s milk kefir, lassi, ordinary yoghurt and Caspian Sea yoghurt (sometimes known as Caucasian yoghurt). There’s the coconut milk versions of each of them, too. And that’s not even touching on the cheese options available.
Then there’s the whole vast array of fermented grains, which are all variations of sourdough of one type or another.
And of course, all these cultures have different recipes, different culturing conditions, and can be very vulnerable to cross-contamination.
It can all get very, very confusing and overwhelming.
What if you already have a kombucha culture growing at home, but you’d like to try your hand at some dairy ferments? Of course, you can source some milk kefir grains, or go get a starter culture for yoghurt.
But can you also just use your kombucha? Will the good microbes in the kombucha work to ferment the dairy?
Today I’m looking at a pair of research papers that say yes. Yes, you can.
The research papers
These research papers both come out of a laboratory at the University of Novi Sad, in Serbia. Unlike the research papers I usually look at, this is food technology research. Which means the researchers are mainly concerned with how they can make new food products, and whether or not consumers will like the food enough to buy it.
Consequently, the research is not about whether or not the fermented dairy product is any good for you. They pretty much take that on face value, based on the other research that has gone into kombucha – they’re producing a fermented dairy product made from a known probiotic, and assume it to be at least as probiotic as yoghurt. Which I think is a totally fair assumption.
What they do spend time looking into is how to make a good yoghurt out of this stuff. How long should you leave it? How acidic does it get, and how quickly? Is 1% fat better than 2% fat? What temperature is best? Which method gives the better consistency? Which tastes better? Which gives a good ‘mouth feel’?
So, what did they find?
Basically. they found that kombucha works pretty well to ferment dairy milk.
They tried it with milk of 1% fat and 2% fat, and found that the 2% fat milk gave a better all over product.
They also tried it with different amounts of kombucha as the starting culture, and found that it didn’t matter at all whether you added 10%, 15% or 20% of the volume to the milk – the results were the same.
In one of the papers, the scientists refer back to some of their previous research into how kombucha ferments sucrose, and state that the temperature of the ferment is also not very significant.
They consider the most significant factor to be time. It’s important to leave your ferment for long enough for the process to finish. In ordinary kombucha, this can be up to a week. But in dairy kombucha, the process is comparatively very fast. When they fermented the milk at 42degC (108degF) it only took 6 to 7 hours to get a good yoghurt.
What makes this worth doing?
The finding that I found to be most interesting was that when kombucha is grown in milk, there is very little alcohol produced.
In normal kombucha, the final percentage of alcohol is usually between 0.5% and 1.5% – not very much, but enough that it’s important to know it is there. Some people can’t have any alcohol at all, due to health concerns, and so kombucha is not a drink they can have.
This research group refers to another research paper which looks at how kombucha ferments different types of sugars. Ordinary kombucha is brewed using plain white sugar – also known as sucrose. According to this other research, when kombucha ferments lactose (the sugar found in milk), little to no alcohol is produced.
I am very keen to get my hands on this research paper, as people are often asking about using different types of sugar with their kombucha, and it would be great to have some concrete information to share with them. Sadly, it looks like the paper is in German, and available by subscription only, so it’s not looking likely.
Personally, I also think it’s worth trying out this new thing because you can! Just like when we tried out kombucha to see if it would work as a sourdough starter (hint: it does), you might find that this makes better yoghurt than you’ve been able to achieve any other way. Or you might hate it. But you won’t know until you try.
I know for me, it’s handy to know that if I want some plain, unsweetened yoghurt for any reason, then I can easily make some up overnight, even if I don’t have any already in the fridge.
But does it actually work?
Well, dear readers, you’ll be pleased to know that I have put this recipe to the test.
Here is my recipe for kombucha yoghurt, complete with photos and little notes that I made along the way (scroll down for those).
- Sterilize your jar(s).
- Okay, so I don’t usually bother to sterilize my yoghurt jar, so long as it has been washed in hot water or just come out of the dishwasher. But because I was doing this for science, I decided to do it properly. I have an old microwave sterilizer from back when my toddler was a baby and needed supplemental feeding, so I used that. Scalding the jars with boiling water would work fine too, for this recipe.
- I used two slightly-larger-than-pint-sized jars, and fermented half the milk in each, because I wanted to see if there was any difference between adding liquid kombucha to the milk or adding a scoby.
- I used 3% fat milk, because that is what we had in the fridge.
- Scald 1 Liter of milk (1 quart) by heating it on the stovetop to 85degC (180degF).
- I used a dairy thermometer because I have one. But if you don’t, heat the milk until it is thick and frothy, but not boiling. Then remove it from the heat.
- Let the milk cool to about 45degC (115degF) and pour into your jar.
- If you don’t have a thermometer, let it cool until it is about ‘hot bath’ temperature – you should be able to hold it without being burned.
- Add the kombucha.
- If using liquid kombucha, add about 10% of your total volume. For instance, I added 50mL of kombucha to ferment 500mL of milk. You’ll need to do your own math to work that out if you’re using weird non-metric measurements, sorry! It’s about three tablespoons for half a quart.
- Or, since if you’re reading this blog you’re likely to have an overabundance of kombucha scobys in your house anyway, add a scoby to the milk.
- As you will see, the scoby worked much better than the liquid kombucha. If you have access to a spare scoby, use it.
- Cover with a clean cloth or paper towel.
- Place the milk cultures in a warm place to ferment.
- I stuck mine in the oven, and turned the oven on very very low for about 10 minutes before turning it off and leaving the door shut. Every 3 to 4 hours I turned the oven on again to keep it warm. I stuck the thermometer in there too, and it says the temperature ranged between low 20s (degC), or about 70degF, and 45degC (about 113degF)
- After 9 hours, my ferments were still just as runny as milk, but they did smell fermenty. When this happens to me with normal yoghurt, it usually comes right if I just leave them alone in a warm place for a whole lot longer. So I did.
- In all, it took about 24 hours for the yoghurt to set nicely. I didn’t get up in the night to reheat the oven (!), but when I checked on the ferments at breakfast time I decided they still needed a little longer, so heated it up to about 42degC (110degF) again and then turned it off, keeping the oven door shut. They were nicely finished by the time we got back from the Saturday morning music lessons and sports games, about 11am – roughly the same time that I had got them started the day before.
And what were the results?
After a 24 hour ferment, I had two jars of quite decent yoghurt.
But if I had to choose between them, the batch I made using the scoby was the definite winner. It was thick, creamy and utterly delicious.
The one made with liquid kombucha was a little bit … slimy. This has happened to me with ordinary homemade yoghurt in the past, and it seems to happen when the ferment takes a bit long to get going. With normal yoghurt I usually blame it on the milk being too cold when I start, or the jar getting too cold, but I know that wasn’t the problem this time. I think it was that the 50mL of liquid kombucha was just too small an amount of starter culture.
Why did I get a different result to the researchers? Well, for a start we have different kombucha scobys. And, as we all know, each scoby is a slightly different mix of microbes. It may be that their scoby was just a bit more vigorous than mine.
Also, I just grabbed the kombucha that was sitting on the bench ready to drink. Currently, we’re only letting the kombucha brew for about 4 days before bottling it, whereas the brew used in the research papers had fermented for a full 6 days at 29degC (84degF). So their liquid kombucha would have been much stronger than mine.
But the scoby-made yoghurt was excellent. So all in all, a great success! I will definitely be using this recipe again in the future.
And don’t worry, I didn’t let the slimy yoghurt go to waste. If you ever get a batch of dairy ferment that is a bit of a dud, you can just use it to replace buttermilk or sour milk in a baking recipe – just thin it down with a bit of milk if necessary.
I used it to make a delicious batch of yoghurt and banana muffins for our afternoon tea.