Fine Tuning and Trouble Shooting the Kefir Making Process


What should it taste and look like?

The kefir should taste yoghurty and tangy but it lacks the slightly sweet aftertaste of yoghurt. If you’ve tasted shop bought-kefir, you might be in for a bit of a surprise at first, but you really can learn to love it. If it makes you wince or tastes very yeasty or sharp, ferment it again in fresh milk and try again. Home made kefir is not as smooth as yoghurt either and might be slightly grainy. It it might take a couple of ferments for your kefir to settle down and get used to its new home – the grains are, after all, an extremely complicated living thing.


What sort of vessel is best for fermenting?

The bacteria and yeasts in the kefir grains work efficiently in an anaerobic environment – that’s without oxygen. When they start to ferment the milk, some carbon dioxide is produced. So you need something that will let this gas out, as well as stopping to much oxygen and air borne bacteria and fungi in.

Clip-top jars with rubber gaskets – Kilner jars or similar, are perfect for this. Kefir seems to like glass containers, and it allows you to see what’s going on.   The sealed jar, with just a couple of centimetres of head room, stops too much oxygen being present, while the rubber gasket allows enough expansion to let out some of the CO2 that’s produced ( perfect for an overnight fermentation).

If you don’t have a kilner jar, or are making a smaller quantity of kefir, you can use an ordinary jam jar. Just be sure to leave the lid a turn undone so that there is not too great a build up of pressure. Always make sure that you clean the lid ( especially metal lids which have a lip) as well as the jar. If you don’t have a jar, you can just use a bowl and clingfilm or a plate over the top.

Technically there’s nothing wrong with using plastic containers. Personally I think that they make milk smell funny but if you are’t worried about plastic things, go ahead – come to think of it, you could just put the grains straight into a plastic pint milk bottle ( as long as you don’t get confused about what is milk and what is kefir – could make a nasty cup of tea!)


How full should the jar be?

Fill the jar with milk so that there are no more than a couple of centimetres of head room. The bacteria and yeasts in the kefir grains are able to grow well without oxygen, or with just a little oxygen present. Many surface moulds, however, require oxygen to thrive. By having just a little headroom in your vessel, you will make it very difficult for contaminating moulds to grow.


What type of milk should I use?

Use fresh milk that is not on the turn – pasteurised milk contains some non-harmful bacteria that can grow at low temperatures and eventually change the flavour of the milk which can make your kefir taste odd. Most people settle on whole milk ( i.e. blue top in any UK supermarket), which gives a good combination of taste, texture and ease of processing but any fresh animal milk works, from skimmed to full fat Jersey ( yum!), goat, cow or even sheep! You can use homogenised or unhomogenised milk. But it’s worth noting that with high fat varieties of unhomogenised milk, sometimes the grains get stuck in the cream and don’t make the milk curdle – if you are using this kind of milk you’ll need to stir or shake it a few times whilst it’s fermenting. My milk of choice is full fat homogenised Jersey which makes a very thick and luxurious kefir, and as I only use 100 mls a day, I figure I can withstand the extra calories. Basically, the richer the milk, the thicker the kefir.

You can use raw milk if you want. I am not personally advocating the use of raw milk, in fact I am not sure about it at all. There is some evidence to suggest that turning it into kefir could be a safer way of consuming raw milk: there are so many “good” microbes in the kefir grains that they can usually inhibit the growth of small numbers of pathogenic (harmful) bacteria that could be present in unpasteurised milk. But on the other hand, studies have also shown that the very nastiest pathogens can survive and even proliferate in kefir cultures ( REF). If you are keeping raw milk at room temperature for 24 hours to make kefir, you would have to accept the risk that if pathogens are in your starting milk, there could be more of them in the finished kefir. Don’t feed to children, the elderly or immunocompromised.

Although UHT milk gets rather bad press as it is felt to be comparatively nutrient poor, if it happened to be the only milk you could get, it would definitely be better than no kefir. The proteins are denatured by the treatment and it doesn’t seem to make a particularly unctuous kefir, but will still have nutritive value from the action of all those microbes. Also, there’s a Russian type of kefir called Ryazhenka made from baked fresh milk which is delicious!


What about metal?

Most domestic grade stainless steel isn’t made for fermenting as the acid tends to corrode it, so I don’t recommend using a stainless steel fermentation vessel.   But short term contact with a metal spoon and sieve for mere moments? – your kefir, and grains, will be fine. Many folk do end up using plastic sieves and spoons though because of all the anecdotal advice that suggests plastic and glass things are better.


When will it be ready?

The grain/milk ratio and the temperature both affect how quickly your milk will become kefir. Put your jar somewhere (out of direct sunlight is best) where you can keep an eye on it. I prefer to catch my kefir when it has just set solid but before it separates into curds and whey. Although they can be mixed back in, the flavour is less strong before this happens. With practice you’ll be able to time it just right. It’s harder to tell with skimmed milk which gives a much softer set. Poke with a spoon if you aren’t sure if it’s thickened. I also like to give it a sniff – if it smells slightly yoghurty or mildly cheesy it’s done. You don’t have to wait until it sets solid – it will still be full of probiotic bacteria if it is thicker than usual milk. Try it at various points.


What should I use to strain my grains?

The hardest thing about making kefir is the logistics of getting the kefir out of the fermenting vessel into the storage jar! At the beginning I used to use a big plastic sieve to strain into a bowl and then transfer using a funnel into a jar. Very messy. After much research I worked out that a funnel strainer is the answer.

My very favourite thing is the Oxo good grips funnel strainer. It’s perfect for straining into a jar or bottle. The strainer comes out so it can be washed. The only thing that is a worry is losing the strainer bit.   They’re a ridiculous price for what is ostensibly a plastic funnel, but you can get cheaper stainless steel versions ( see “what about metal” above!). If you think a daily dose of Kefir is going to work for you and your family, it’s definitely worth investing in one of these.

I have seen some people try to solve the logistical problem by keeping their kefir grains in a little muslin bag attached to an external string that can be pulled out of the fermentation vessel instead of straining. Whilst on many levels this seems practical, it’s not for me.   The milk curds can build up on the bag and become quite sour and it all ends up looking a bit grubby … I like to look at my kefir grains every day – see how they’re doing, and know that the only thing in my kefir jar is my milk and grains.


How many grains should you use? What’s the ratio?

In my instructions I specify a thumbnail amount of kefir grains. “But what if I have small thumbs?” or “ what if I have large thumbs?” you may ask. The thing is, it doesn’t need to be exact. The microbes in the kefir grains multiply exponentially by cell division. That means that when they are ready to grow, one cell splits to become two cells, two become four, four become 8, then 16, 32,64,128, 256,1024, etc….. Here’s an example. At room temperature, many Lactobacilli double about once every hour or so. So after 18 hours from one single bacterium you will have over 200,000 bacteria. You’re already starting off with millions in the kefir grains so you’ll probably end with about a billion per 100 ml – though I am not counting them!   At any rate, if you start with a big, small or even tiny lump, you will end up with A LOT. Besides unless you have electronic scales it’s hard to measure less than 10g, so the fingernail guide will do just fine!

I also recommend that you use a much smaller ratio of grains to milk than other kefir-producers suggest. I wouldn’t use more that 20 g/litre – so that’s effectively 2% w/v grains/milk. If you have too many grains, you end up with quite a different composition in your kefir – It can become rather yeasty and fizzy and taste extremely sour or vinegary L. Then the yeasts and acetobacter sp. will predominate giving you stronger flavours as opposed to the better balance of lactobacilli, streptococci and leuconostocs you get with fewer grains.

This becomes more important if you want to give your kefir to children. If you use too many grains and the kefir becomes fizzy it’s a sign that a lot of carbon dioxide and a small amount of alcohol are being produced ( though likely to be less than 1%).



This can be tricky as 18 hours is not a very convenient time! Try and find somewhere in the house that is slightly cooler and then you might be able to get them to work every 24 hours. If not, they way I get around this is by putting them in the fridge when done and straining/placing in new milk at the same time every day at my convenience.


My grains are growing what is to be done?

Good! That means that they are happy! If there are too many grains in your fermenting jar, as explained above, your kefir will start to taste different. When your grains have about doubled in size, take out half of them and give them to a friend. Or the dog. Or freeze them just in case you murder yours at some later stage J.


How should Kefir be stored? How long does it keep for?

Once strained, your kefir absolutely must be kept in the fridge. It is jampacked full of bacteria and yeasts that will keep on fermenting for as long as a food source is available. I suggest that you keep it near the back of the fridge where it’s coldest.   This will stop the microbes in their tracks and is the very best way of helping it keep. It should remain pleasantly useable for up to 5 days. Gradually it will become sourer and sourer until it’s good for nothing except baking with (see below!).


My Kefir looks funny

Upon storage, it can separate into tiny little curds in whey. Don’t worry – just whisk it up with a fork or small balloon whisk and it will re-incorporate. If it doesn’t smell or taste unpleasant it is fine. If it has a dry white mould on top see below……


Contamination Problems

Contamination is not going to be a huge issue, especially if you use an almost-full clip-top jar with a gasket, or jar with a clean lid. This provides a good low-oxygen environment and it’s difficult both for surface moulds to grow, and for contaminants to enter the jar. There are so many millions of bacteria in the kefir and grains that it is difficult for pathogens and moulds to take hold. Bacteria and yeasts produce antibacterial substances that inhibit growth of other species. Also, kefir is acidic, which inhibits the growth of many pathogens. If you are using pasteurised milk, it has already been treated to kill pathogenic bacteria.

Contamination is more likely to occur post fermentation – putting used spoons into your kefir jar for example… and even then, the same protection from billions of protective bacteria applies. If there’s a dry looking white mould growing on the top of your kefir, which is the only type of contamination I have ever come across, rescue is certainly possible. Strain the grains and wash two or three times in small amounts of milk. Then place in a smaller than usual jar ( so you don’t waste lots of milk) and fill it very full to eliminate as much air as possible. Ferment as usual and see if it’s done the trick. Try once more if the mould is still present, or start again from your frozen spares.


When you’ve got too much

Sometimes people get going with great gusto then find that they are over run with the stuff sitting in jars in the fridge. If this happens, the first thing you need to do is stop making any more! There are various things you can do, depending on how long a break you want to take.

  1. Short break ( < 3 days)

Put your kefir in the fridge either

a) when it has set before you strain it, or

b) after straining in its fermentation jar full of fresh milk.

When you want to get going again, just put the jar out on the worktop to get going again. It might take a little longer as it will need to come up to room temperature first for growth to begin apace.

  1. Longer break (> 3 days < 2 weeks)

put grains in a smaller jar of fresh milk ( 10% w/v grains/milk approx.). They will still grow but slowly and set kefir may or may not result. If if does, it might taste fine, but it might well taste a bit odd, as the bacteria that make milk go off will be active too over that timescale (these won’t hurt you, but it is a reaction that is going on in the background). Use a smaller amount of milk because if it’s been a fortnight you’ll just want to start again.

  1. Even longer break (> 2 weeks < 4 weeks)

Put grains in larger jar of fresh milk ( 5% w/v) and expect to dispose of this milk and start again.

  1. Even longer break – put grains in a bag in the freezer.

The second thing you want to do is look at the recipes at the end.


Can Everyone Have Kefir?

Almost. It’s worth bearing in mind that these are uncharacterised kefir grains – the exact bacterial and yeast composition of them is not yet known (though I am working on it!). I have not been able to find any reports of serious illness arising from kefir consumption, but if you are immunocompromised, or with an underlying serious health condition please do check with your GP. It’s even suitable for many lactose intolerant people for multiple reasons. Firstly, during fermentation much of the lactose is broken down into glucose and galactose by the lactobacilli which are the predominant bacterial species in kefir. Secondly, some of these lactobacilli die during transit through the gut, relseasing the enyzymes that can digest lactose into the small intestine. Thirdly, the kefir microbes that do survive the passage through your upper intestines are able to help your existing gut bacteria to eliminate undigsested lactose.


How much kefir is a good idea?

Please Start Slowly. Occasionally, people have gone at it with gusto and the massive sudden influx of new bacteria species has caused diarrhoea. Please start with just a teaspoon or two the first day, and build up slowly – 5, 10, 20, 50, 75 to a maximum of 125 mls I would suggest. This is a perfect sized portion for some muesli or to form the basis of a daily smoothie. Stomach acid levels are lower in the morning. For this reason it is often suggested that kefir is taken in the morning to increase the chances of the bacteria and yeasts surviving their passage through your gut to your colon!


You’ve made your kefir – what should you do with it?

Your strained kefir can go straight in the fridge if you want to have it plain. Refrigerating it for a few hours certainly improves the flavour and also the texture as it tends to thicken a little. It might separate upon standing – don’t worry, a quick whisk with a fork will re-homogenise it.


Add some flavour

Many people prefer to flavour it up a little to disguise the slightly worthy flavour. Lemon works particularly well – just add a little slice of lemon rind before you pop it in the fridge, or a little lemon zest. If you are feeling extravagant, you can add a single drop of lemon oil, which gives the flavour without causing the kefir to curdle which can happen with the lemon. Some people add lemon juice which can make it fizzy, which is not something I personally need in my kefir, but up to you! Orange or grapefruit can be nice too. Other types of fruit don’t necessarily impart their flavour particularly well just sitting in kefir and are best mixed in as smoothies. Try and avoid the temptation to sweeten it with sugar or honey. This is supposed to be good for you after all, and we all eat enough sugar.