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The real reason kefir separates is because the milk has become acidified. The kefir grains are made up of bacteria, yeasts and fungal cultures which use the milk sugars for energy. Specifically the lactic acid bacteria produce an acidic environment which protects the culture from invasion from pathogenic bacteria.
As a result the kefir becomes acidic and once it reaches a PH of 4.6 the protein in the milk will begin to solidify and float to the top of the jar.
This is a good thing because you don’t want pathogenic bacteria in your kefir. You want fresh good tasting kefir to drink.
This happens in any milk with a lower PH. In fact it is a trick for those who want to make buttermilk pancakes but don’t have any buttermilk. They simply add some vinegar of some type and the milk curdles.
Here are 5 reasons why your kefir may be separating
1. Long fermentation time
Kefir is a living collection of bacteria, yeasts and fungal cultures which require food to live. This food comes in the form of milk sugars (mostly lactose) which the various cultures in the grains break down and use for energy. In the process of milk carbohydrates are converted into energy and lactic acid is produced and the milk acidifies.
This is a natural process and is why kefir has that nice slightly tangy flavor when it is freshly made. The key is to determine at what point you need to stop the fermentation and refrigerate or consume your kefir.
The longer the grains are left in the same batch of milk the more acidic the milk will become. This causes the curdling effect and the kefir will continue to separate until all the food energy are consumed.
To prevent separation you could try a shorter fermentation time but since kefir production is continuous to maintain a routine try to keep it in 12 hour increments.
2. The number of grains in the milk
Another factor is the number of active cultures which are consuming the milk. This is controlled by the amount of kefir grains which you add to the fresh milk. The more grains the more LAB which will be present to convert the carbohydrates in the milk to energy producing lactic acid and lowering the PH of the milk.
It is like ordering pizza for a bunch of teenagers. You know that all the pizza will be eaten but the ratio of pizza to teenagers will determine how long it takes them to eat it all. The more teenagers the faster the pizza will disappear.
The ideal ratio for kefir grains to milk is one to ten. This will produce kefir which is thickened nicely, will not be too sour and will have a nice slightly tangy flavor. The one to ten ratio helps the grains to remain healthy and grow well.
To keep your kefir from separating use less kefir grains for each batch but make sure your kefir thickens within a 24 hour period as too few grans may not be able to acidify the milk before unwanted bacteria start to grow giving the kefir an off smell.
3. The temperature of the room
The bacterial cultures in the kefir grains are affected by the ambient temperature of the room which they reside. This is why when you want to take a break from kefir production you put your grains in the fridge.
The range which kefir grains are active is between 60 to 90 degrees Fahrenheit. Therefor your kefir grains will be active anywhere in this range but the cultures are more active if they are cultured between 70-80 degrees Fahrenheit.
Each temperature change will favor a different selection of the population of the grains culture. If you are in the hotter zone then the cultures will be very active and produce lactic acid quicker than if they were cultured in a cooler temperature.
To slow the grains down place the fermenting kefir in a cooler place.
4. The type of milk
All milks contain different amounts of energy which ferments at different rates. Milk with high amounts of available sugars in it will ferment faster than milk with sugars which are harder to ferment.
Lower fat milk tends to acidify faster than milk with a high fat content. The percentage of available sugars in the milk is lower with high fat milk. This means that the kefir culture will first have to convert the milk fat into sugars which are then made available to the lactic acid bacteria. This process takes time and as a result will prevent the kefir from separating as quickly.
The type of animal the milk comes from also determines the available sugars in the milk.
The percentage of lactose in cow’s milk is about 5%, goat’s milk is 4.33% and sheep’s milk weighs in at 4.76%. Each of them have a different amount of easily fermentable sugars and therefor will acidify at different rates.
Try using milk with a higher fat content or a different type of milk. They will all produce a kefir with a different flavor and constancy and separate at different rates.
5. How active the grains are
This is determined by the history of how the grains have been treated.
If they just came out of the fridge after you have taken a break from making kefir it might take a little longer, it may have been hot in the kitchen for a while so the grains will be extra active or you have not paid attention to how fast your grains have been growing and there are too many grains for the amount of milk.
Active grains is good. This shows that they are healthy and growing which is something you want for your grains. The challenge is to figure out a balance between the rate your kefir grains make kefir and what works for your schedule.
What to do about it
The first thing to do is to strain the grains out of the kefir if you have not already done so and then shake the jar to disperse the milk proteins to mix the whey back in. Pour yourself a glass and taste it. If you like the flavor then refrigerate it and consume it within 24 hours or so.
The kefir cultures in the milk are still alive and require energy to live so they will continue to acidify the kefir even in the refrigerator so don’t be surprised if you leave your kefir in the fridge for a week and then pour a glass only to find it is too sour to drink. It is best to consume your kefir quickly once it has reached the flavor you like.
If you find the kefir too sour then you will need to adjust your method of making your kefir.
Sometimes it is difficult to determine just which factor to change to get the kefir which you like the best since each of these variables effect the flavor of the kefir in varying degrees.
To determine the best mix of these variables you will have to do some experimentation.
A longer fermentation time will change the population of the various cultures in the kefir. Yeasts and lactic acid bacteria which can survive lower PH levels will continue to grow whereas the ones which are sensitive to the PH will be inhibited.
The same goes for the other variables
As the population of the culture changes so does the flavor of the kefir. Each yeast and lactic acid bacteria will produce a different flavor. To get the flavor you want in a convenient period of time you will have to change the conditions which you ferment your kefir in a systematic way.
Keep a logbook or diary which records the time the kefir fermented, the temperature, how many grains were added and what type of milk you used.
Then change one of the variables for each batch. Note which changes improved the flavor and which ones were not to your liking.
Make a few batches before determining the results as it may take a while for the kefir flavor to stabilize with the new conditions. Keep notes about what changed and if you liked the result.
Some variables favor the yeast growth and some favor the lactic acid bacteria. The goal is to find the conditions which produce the kefir which you like the best and then have a record of it so you can closely reproduce it over and over.
It may be that you like your kefir like I do
I like to ferment mine for 24 hours at 18-22 degrees with about 1:8 ratio grains to milk in homo milk. I then strain the grains and sometimes if I want to make cream cheese or almond pancakes I will leave the kefir to ferment without grains for another 24 hours under the same environmental conditions. This further acidifies the kefir and will produce a well separated kefir which is ideal for making cheese and the lower PH also helps protect the cheese from spoilage as well as helping the pancakes rise better.
What the specific conditions are which make the kefir which you like may be entirely different than others. It doesn’t matter just as long as it produces a kefir you like.
Can I still drink it?
Of course! Kefir which has separated has not gone bad. In fact for some of us it is better to ferment for a longer time. Those who are lactose intolerant will find it easier to digest kefir which has a lower PH because this means there is less lactose (the sugar in the milk) present.
Kefir grains produce an environment which has a lower PH. With a lower PH the unwanted microorganisms which are present in your environment cannot grow in the kefir. This protects it and you from pathogens which can make you sick.
What to do with kefir which is too sour to drink
You may not like the taste of kefir with a low PH but that does not mean that it has gone to waste. It may not be to your liking to just drink but there are lots of things to do with kefir which is to tart.
You could add it to a smoothie, make thickened soups and sauces or make cheese.
Check out my post on things to do with over fermented kefir. It will provide you with a wide variety of options.
If this seems like it is too complicated it’s not. Making kefir is one of the easiest fermentations you can make. It only takes a little bit of time and once you have found the method which produces kefir which you really like you can continue to make it indefinitely.
Which is a great thing. It is cheaper, is always fresh and has more probiotics in it then most store bought versions. You can make it with any type of milk including nut milks like almond, soy and cashew milks. I even make kefir with pumpkin seeds which is great for a morning smoothie or to pour on top of a bowl of cereal.
The bottom line
Feel free to experiment and try different things. Kefir grains are very resilient and can take a fair amount of abuse but to get consistent kefir you enjoy you need to know what the conditions are which will produce that kefir. The only way you can do that is to try different things until you get what you want.