Choosing the Right Container For Making Dairy Kefir

So you have tried a friend’s wonderful kefir brew and perhaps they have offered to share some spare kefir grains with you or you are going to purchase some from a reputable supplier but you are wondering what the best container is to hold your precious brew.

Wonder no longer as this article will explain all the best options, as well as steering you away from the wrong options. Make sure you read our how to make kefir article first!

Fermenting kefir essentially only takes one initial container although there are other requirements should you choose to make a second fermentation or store some either in your refrigerator or a cool spot in your home.

All containers are not created equal but whichever one you choose make sure it does not affect your kefir in any way.

Note, this article relates to Milk Kefir, not water kefir. While both ‘kefir’ types can be made in the same sort of container, there are some differences in the brewing methods. You’ll probably want to use different types of containers for Water Kefir and Milk Kefir due to the radically different textures of each kefir type.

Types of Containers Suitable for Kefir Making (especially milk kefir)

Glass Containers

# 1 Glass containers with thick walls and wide open mouths are often first preference. Glass, as a stable inert material, will not react to kefir acidity nor does it break down over time with a danger of releasing any toxic chemicals such as bisphenol A (BPA) into your kefir. Glass is transparent so that you can see how the fermentation process is developing, is resistant to scratching and easy to clean. Glass containers are easy to obtain and relatively inexpensive.

The only real negative is that they are fragile in the event of an accident and you may lose your precious grains (another plus for having extra grains in storage). Some people do not wash their glass containers every fermentation, perhaps only every second or third or once a week, without causing any problems which avoids risk of damaging or breaking the container. Crystal contains lead so best to avoid using crystal glass.

Clay Containers

Clay containers made with various types of clay may also be suitable for fermenting kefir. Ceramic containers have some similarities to glass but it does depend on the glaze used to seal the clay. It is important to check that it is indeed a food grade glaze. The colors of glazes are produced by various elements so any glaze that contains a heavy metal, again such as lead, should be avoided. Food grade porcelain is generally acceptable to use for kefir.

Care must also be taken with terracotta as it can also be contaminated by heavy metals so should be used with caution. You can take the precaution of sealing ceramic, terracotta and stoneware containers with quality natural beeswax – see note below. However these containers have the disadvantage of being opaque so you cannot check how the kefir is fermenting.

Plastic Containers

Plastic containers are also an option but as always it must be food grade plastic to ensure there is no possibility of leaching of any toxic substances like BPA as the plastic breaks down in the presence of kefir acids. Plastic is durable and can be transparent or translucent which allows you to see the progress of the fermentation process. However there is still a possibility of scratching damage that may make it difficult to clean completely and all plastic does tend to start degrading over time.

Metal Containers

Metal containers and utensils cause quite some discourse and debate so I will try to give you the facts so you can decide for yourself. some dedicated kefir ‘fermenters’ vow and declare never to let so much as metal pin touch their kefir, while others alternatively continue to regularly ferment in food grade stainless steel containers with ongoing success. Others err on the side of caution and use metal utensils but shy away from actual containers. So where does that leave you?

Kefir production was only spread among the wider world early in the previous century but food grade stainless steel was not available then, nor was plastic so it was only natural that people might attempt to ferment acidic kefir in durable metal containers. However in those times, metal containers used for food traditionally were made of iron, brass, and copper.

The organic acids in traditional milk kefir would have reacted with these metal containers releasing metallic ions and tainting the kefir with unpleasant flavors, perhaps even colors. Of course any heavy metals in alloys, like old pewter would have been dangerous to ingest over long periods too if they were being degraded by food acids. Now that inert food grade stainless steel is readily available it is possible to ferment milk and water kefir, which is not acidic anyway, in such containers. They are of course very durable but like ceramics do not reveal the fermentation process.

So to summarize, it should be fine to use food or medical grade stainless steel for fermenting milk kefir but all other reactive metals like cast iron, brass, copper, zinc, pewter, or aluminum should be avoided. Kefir made with water and sugary kefir grains (SKG) is not acidic so is not subject to the same limits however I feel it is wise to use the same precautions regarding container choice.

Leather Containers

Leather… last and possibly least with today’s refined attitudes, you could always use leather as the natives of the Caucasus used in days gone by. Goat skins were used to carry and store milk and it was a happy accident that the milk turned sour but remained safe to drink and over time, reusing the same leather carriers it appears that the lactic acids and bacteria from the milk and skins gradually formed polysaccharide matrices known as kefiran that developed along with the original kefir grains. These pouches were never completely emptied so a continual fermentation process developed.

To summarize and make a personal recommendation I prefer open mouth strong glass containers over any of the others – glass is obtainable, inert, non reactive, easily cleaned, transparent and attractive however ultimately the choice is yours.

What Container Material is Best For Making Kefir

Typically, we say that glass is the best. It’s cheap, widely available in many shapes, and non-reactive to the fermenting kefir. You can opt for stainless steel, leather, or plastic, but with the wide availability of glass containers, there is no reason why NOT to use glass.

Whichever options you choose always make sure that your chosen container is filled only to 3/4 to 2/3 full at the beginning of your ferment.

Fermenting kefir releases carbon dioxide so the liquid thickens and bubbles, increasing in volume so the gap is needed to ensure it doesn’t bubble over or increase too much pressure in a small air space.

How Large a Container?

Just how large the container needs to be will of course depend on how many grains you are starting with ad much kefir you and your family intend to consume, so choose one large enough for your daily ferment. It is usually better to make small regular batches, than to stop, start and have to put grains in storage.

See other articles to learn how to “rest” grains should you decide to have a break from making kefir.

Note: For an exact list of actual product recommendations for brewing kefir, please read our Best Containers for Making Kefir article and our Best Equipment for Making Kefir article.

Should You Seal Your Kefir (Sealing vs Unsealed Lids for Kefir Making)

Kefir Fermentation is primarily Aerobic

The initial fermentation process to make kefir from milk or sweetened water is aerobic, that is, it needs oxygen to complete the process well. That is one of the reasons that one should never fill your container more than 2/3, ¾ full to allow an air space, which of course is full of life giving oxygen. The other reason is that carbon dioxide bubbles will form within the kefir making it fizzy and also increase in volume to fill the space at the top of the container.

However, Kefir can still be made in an anaerobic (no oxygen) environment too. If you seal your kefir, it will still ferment.

However, kefir grains reproduce BETTER in an aerobic environment. If you take two bottles with kefir, seal one and leave the other unsealed, you’ll find the unsealed bottle after several days has more kefir grain reproduction than the sealed version.

We know it needs air but we also know kefir is delicious and other creatures think so too, like fruit flies, ants and other bugs that may try to take a last breath swimming in your kefir so need some way to keep them out. You also want to make sure dust, hair from pets, or any other foreign objects do not contaminate your kefir.

When to Do Anaerobic Kefir Fermentations Over Aerobic Fermentation

There may be some occasions when you prefer anaerobic fermentation:

1. to block out wild yeast from landing in your kefir adding unwanted flavors
2. during a second fermentation with extra flavors added to the kefir once the grains are removed

Personally, if it’s a very hot environment and / or there is risk of yeast penetrating into the kefir (which can happen, even when you put a napkin or cloth over the top), I will do a sealed kefir fermentation. As long as you shake the kefir and don’t keep the kefir fermenting for more than a couple days, you often get a BETTER tasting kefir because you bock wild yeast populations from blooming on the surface of the kefir.

What to Seal Your Kefir With

At very least you should cover your kefir with a paper towel, coffee filter or smooth cloth (nothing that will lose lint) secured with a strong rubber band or other cord. You might also opt for a mason jar with a metal band, (refer my previous paragraph regarding what metal is suitable) and replace the metal disc with a plastic one or gauze as a breathable cover. I have used a plastic lid and cut the center out with success before, using a mesh across the top.

Kefir fermented in an unsealed container is less fizzy and you can always do a second ferment if you want to increase the fizz later over a few days.

Shake Your Kefir For Better Flavors

Kefir also prefers gentle agitation during ferment to ensure all the milk is exposed to the working grains. If you don’t shake it (like the goat skins used to get gentle knocks by passersby in the entrance way) the grains don’t do a full fermentation and the kefir surface area can be more easily exposed to “wild” organisms. So gentle shake ups during the daily fermentation are a good thing and to do this you may prefer a sealed top.

Sealed tops are good for shaking but not so suitable for releasing gases built up during fermentation. You can either leave the lid slightly loose to release gases and just tighten when needed. Or you can schedule to burp your “baby” kefir regularly during the day to make sure built up gases are released. If you forget and leave it sealed though be aware there may a fizzy explosion, not mention overflowing mess, when you try to open it later. What you choose will depend on your lifestyle and working day.

What Happens If You Seal Your Kefir Too Long

If you are particularly forgetful or some other disaster struck and you had to leave your sealed kefir for a longer time, say over 36 hours or more, you may return to find you have produced carbonated wine of kefir which may or may not be to your taste. The build-up of gases can also be dangerous as the pressure could cause breakages in glass containers (like my mother’s exploding ginger beer) or popped up metal lids stretched to capacity. Approach with caution!

So there you have a fairly comprehensive list of what sort of containers are suitable to make your kefir in whether it be milk kefir or SKG water kefir. I prefer to use a strong glass container like a mason jar, taking the extra care because of its fragility and I cover it using a plastic rim and a breathable material across the center. I still agitate it whenever I am in the vicinity or remember but my lifestyle means a sealed unit would not be suitable if I couldn’t release the gases regularly.

Get by with a little Help from Bees

Here is some information for those interested in sealing any containers or utensils with bona fide beeswax (never paraffin or candle wax). Beeswax will give the extra assurance that no toxic materials can contaminate your precious kefir.

Place the desired container into a warm oven at 230oF (120oC) until warm through. Remove with care and rub beeswax all over the inner surfaces, sides and bottom to makes sure the wax can penetrate to form a complete seal. If the walls are too cold the wax will only set on the surface then peel off rendering it ineffective. If you do not have a suitable oven then you could use a heat gun or hair dryer to warm the surface before applying the beeswax. The latter is preferable for coating plastic surfaces as at no stage do you want the plastic near melting point.

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