Kefir is like yoghurt in a lot of ways and it's delicious too but it's not yoghurt.
Kefir cannot achieve the same density and set that you get in yoghurt.
Yoghurt has a smooth, creamy, rich texture that is hard to match.
There are two things that make yoghurt what it is:
Yoghurt is made from milk that has been cooked at or above 85C to modify the proteins, enabling them to bind liquid.
Yoghurt is cultured at a high temperature (45C). The heat suits thermophilic bacteria, but kills other bacteria.
The result is a richly textured creamy food and, unlike thick kefir, it is not sour.
Making yoghurt at home
I know a lot of people make yoghurt at home. They add sachets of dried ABC lactobacillus (Acidophilus, Bulgaricus, Casei) to cooked milk and get a very good product.
Most people re-use that yoghurt to make more yoghurt.
The first few batches are perfect but sooner or later it starts to go wrong and you are back at the shop buying more culture, wondering why you can't keep your yoghurt alive.
The fact is, you are doing everything right.
You can make yoghurt perfectly well when you have a good, strong starter culture.
Things only start to go wrong after a few batches because airborne yeasts and bacteria have found their way into your yoghurt .
Cooked milk is so nutritious that everyone (in the bacteria world) wants to have some.
Whether you are starting from a sachet or a dollop of shop-bought yoghurt, the commercial cultures are typically made from one or more of the ABC lactobacillus.
These milk-loving bacteria make delicious yoghurt. Unfortunately, even in combination they are no match for the many,
many different microbes that will try to colonise your yoghurt. Eventually the wild cultures dominate and you know how the story ends.
On the other hand:
Kefir contains a more diverse community of bacteria and yeasts than ABC yoghurt.
Kefir is able to suppress invasive bacteria.
Can we combine the good bits?
Kefir contains many different species and in combination they are able to maintain a stable environment that suits them and deters other species.
If we use kefir to make yoghurt can we get the yoghurt yum with kefir resilience?
Yes! We can - although there is a small "but."
"But's" don't sound good, so let's get that "but" out of the way right now. One way to put it is: the second batch will be great!
The first time you use kefir to make yoghurt you end up with a yoghurt that's OK but nothing to write home about.
There's a reason why the first batch is ok-but-not-great and we'll talk about that now.
Kefir is like a rainforest wilderness teaming with life.
When you put them into hot (45C) milk many species will die.
The species that are able to withstand high temperatures will survive.
Your first batch will reflect the struggle that was taking place at a microbial level.
OK. How do we do it?
Make yoghurt as normal using a few tablespoons of thin or thick kefir as the starter culture.
The first batch is transitional. It will make an ok yoghurt.
Depending on the state of your kefir the first batch may be almost perfect or it may be a little acidic.
Don't be deterred if the texture isn't right or it splits.
The first batch is in transition from a multi-floral kefir to a specialist community that makes yoghurt.
When you're ready to make a second batch of yoghurt, use a few tablespoons of your first batch of kefir-yoghurt as the starter culture.
This time around its like putting thoroughbreds onto open fields of clover. You are using a select group of heat-loving-specialists.
This community of thermophilic bacteria are completely happy being pitched into hot milk.
They'll produce delicous yoghurt and you can make yoghurt forever* from your kefir-sourced yoghurt cultures.
We have a friend using yoghurt culture that has travelled to New Zealand from Holland, it is said to be 25 years old.
Our yoghurt culture made from our kefir is used to make yoghurt once or twice every week.
It's not 25 years old yet, but the kefir granules that provided the culture are descendants of kefir cultures that are very old.
No-one is sure about the early sources of kefir. There is a presumption that it developed after the domestication of animals for milk.
If that is true then kefir is thousands of years old and there is no reason to think that the yoghurt cultures selected from kefir will fail any time soon.
Warning: don't ever put your kefir granules in hot milk!
Put one litre of milk into a heavy bottomed pot and bring it slowly to 85C
Use a pot with plenty of spare room. Milk expands rapidly when it boils, and you don't want it to spill.
Stir the milk as it heats to prevent it sticking to the bottom
You'll know that it's near 85C when small bubbles are forming on the surface
Hold the milk beneath boiling point for 5-10mins, stirring all the while
If the milk does boil, that's OK, just take it off the heat and continue
Now cool the milk to 45C.
You can do this by waiting and stirring.
I prefer to put the pot into a sink full of cold water, stirring to facilitate heat exchange.
Place a couple of tablespoons of yoghurt culture into a container.
Add the hot milk to the culture in stages. Add a little at first, blending thoroughly until its smooth, then adding the remainder and mixing thoroughly.
Move the container into a thermos or a place where it will stay warm and leave it to sit for 6hrs or more.
Store your yoghurt in the fridge or a cool, dark cupboard
Troubleshooting: What could go possibly go wrong?
You know the W. C. Fields gag: never work with animals or children. Things will go wrong.
At one stage or another you'll have a mishap. You can be sure it happens to all of us from time to time.
Fortunately, when it comes to kefir-cultured yoghurt, the causes may differ but the solution is almost always the same.
No matter what has happened, take a couple of tablespoons of your yoghurt culture and start again
Most common problems are caused by using old milk
Splitting, sourness, off smells and bubbling will occur when you make yoghurt from old milk
Use fresh milk, a few tablespoons of yoghurt and start again
Similar problems occur when your yoghurt culture gets tired and hungry
Regular feeding, also known as making yoghurt more often, cures these problems.
Take one tablespoon of your hungry culture, some fresh milk, and start again
You may have problems if your utensils weren't clean and dry
Clean and dry does not mean sterilised, bleached or anti-bacteria'd.
Clean means no left-over bits stuck to surfaces, no oily surfaces, no sticky goop, no dust nor lint.
Dry means no moisture left on the surface.
Always use utensils that are clean and dry.
My yoghurt has split into curds and whey
Milk splits when temperatures and acid levels are high.
Common causes are:
The milk was old (already acidic)
The milk was too hot when you added it to the culture
Your starter culture was acidic, see "tired and hungry"
You added too much starter culture
If you think your starter culture was the cause of the acidity ( tired or hungry starter culture ) then reduce the amount of culture you use to start the next batch of yoghurt.
The solution is to make a fresh batch.
My yoghurt is bubbling
Gas producing species are a normal part of the kefir community. If these species are prevalent you'll get bubbling in your yoghurt.
A little fizz doesn't affect the flavour much and sparkly yoghurt is fun.
Because the effervescent cultures are normally present in these communities,
it may take a couple of batches before your yoghurt recovers it's balance.
Always use fresh milk. Start again with a reduced amount of starter culture.
My yoghurt doesn't set
Setting occurs when the milk has been cooked at a temperature sufficiently high to denature the casein and whey proteins that are in milk.
Ensure that you are cooking the milk for 5-10mins at a temperature between 85C and boiling point.
I want to make "Greek" yoghurt
Commercial producers of thick or "Greek" yoghurts usually include milk powder to change the ratio of milk solids to liquids.
That's something that you can easily do in your own kitchen too. Experiment until you discover the perfect ratio.
The traditional method is to strain off some whey by hanging the fresh yoghurt in cheesecloth overnight or until it's at the thickness you want.
This is the method I use. It's simple and it doesn't require any effort or attention. Catch the whey in a bowl and use it instead of milk for soups, cakes, scones, batters and sauces
Reducing the volume of milk by boiling will make a dense yoghurt too. This method increases the cooking time and requires more care and effort than the others.
Each of these methods produces a slightly different yoghurt. Use whichever you prefer.
Any Other Problems?
Use fresh milk, a few tablespoons of yoghurt and start again