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Although kefir and yogurt are both fermented milk products which thicken the milk they are different in several ways.
| Kefir | Yogurt |
| Fermented at room temperature | May need added heat |
| Fermented with grains | Fermented using backslopping |
| Usually a thinner consistency | Usually a thick consistency |
| High number of probiotics | Fewer number of probiotics |
| Probiotic colonization | No probiotic colonization |
| Contains alcohol | Does not contain alcohol |
| Can be second fermented | Not usually second fermented |
| Tangy flavor | Creamy smooth flavor |
| Aerobic fermentation | Anaerobic fermentation |
Fermentation temperature
Starter cultures for milk fermentation come in two temperature groups.
- Mesophilic: Will culture at room temperature
- Thermophilic: Needs heat above room temperature
The difference between the two is the variaty of species found in the culture. Some species perform best in cooler temperatures and some like it warmer. When most of the species found in a culture performs the best in cooler temperatures the starter will be mesophilic. The opposite is true for Thermophilic.
Kefir is mesophilic but will culture in a wide range of temperatures.
This is because the type and number of cultures which are involved in the fermentation of milk into kefir. Milk inoculated with kefir grains will ferment slowly in the refrigerator, faster on the counter and even faster if heat is applied. Although the kefir will taste different with each method the milk will still thicken and sour in all cases. To learn more about how the temperature affects kefir read Five Reasons Why Kefir Separates: Plus the Real One.
Yogurt can be made both ways as well but the difference is that the starter cultures for mesophilic yogurt and thermophilic methods are different. This means that if you have thermophilic starter it will not ferment properly at room temperatures. Instead it needs to be heated up to between 100°-110°F. This can be done by:
- using the oven with the light on
- using a cooler with hot water bottles
- using a yogurt maker
Mesophilic yogurt starters can also be used and there are several on the market. They are to be used at room temperature within 70°-77°F. There are several types of this yogurt starter which contain different bacterial strains depending on the source of the culture.
Starter Culture Type
Kefir is made one of three ways:
- Backslopping already cultured kefir into fresh milk
- Using a powdered starter
- Using kefir grains (a symbiotic culture of bacteria and yeasts)
The three ways are expained in the post, Three Ways to Make Kefir: An Illistrated Step by Step Guide.
The only method which can be used to continuously make kefir is with kefir grains. Kefir grains are made up of polysaccharides and proteins which the various cultures in the kefir create to protect themselves from pathogenic bacterial invasion. It is made by adding fresh milk to the grains which the cultures in the grains use for food. This way the cultures can continue to multiply and produce healthy good for you kefir.
Yogurt does not have a solid culture medium like kefir does but rather it is a collection of bacterial cultures which work together to transform the milk into yogurt.
There are two ways to make yogurt
- Backslopping already fermented yogurt
- Using a powdered yogurt culture
With yogurt the backslopping method is used for making yogurt from store bought yogurt as well as the heirloom type which will continuously produce yogurt just like kefir grains will.
The difference here is that the store bought yogurt starter will only work for a few times before it gets contaminated with spoilage bacteria. When this happens the milk will not smell edible and usually curdles. This happens because the number of cultures in store bought yogurt is only a small number of the cultures in heirloom types.
Heirloom types will make yogurt as long as you keep some freshly made yogurt to inoculate the next batch.
The powdered yogurt culture can contain one time use starters or heirloom types the type depends on the cultures in the powdered packet
Number of probiotics
When kefir is made with kefir grains the amount of microorganisms in the resulting kefir is high. Studies have repeatedly shown as high as 60 different probiotic strains from a wide variety of types are present in any one kefir grain sample. Each grain has a variation of cultures depending on their heritage, current environment and time of year. Some strains are stronger in a warm ambient temperature and some are stronger in cooler temperatures. The result is a strong symbiotic culture which can produce healthy, good for you kefir indefinitely.
Here is a list of the currently known cultures which have been found in kefir. This is not a complete list and not all of these cultures are found in every set of kefir grains.
| Probiotic strains found in kefir |
| Acetobacter acetic |
| Acetobacter fabarum |
| Acetobacter lovaniensis |
| Acetobacter orientalis |
| Acetobacter rancens |
| Acetobacter sp. |
| Acetobacter syzygii |
| Acinetobacter sp. |
| Bacillus sp. |
| Bacillus subtilis |
| Bifidobacterium bifidum |
| Bifidobacterium sp. |
| Brettanomyces sp. |
| Candida inconspicua |
| Candida krusei |
| Candida lambica |
| Candida maris |
| Candida sp. |
| Cryptococcus sp. |
| Dekkera anomala |
| Dysgonomonas sp. |
| Enterococcus durans |
| Enterococcus faecalis |
| Enterococcus sp. |
| Escherichia coli |
| Gluconobacter frateurii |
| Gluconobacter japonicus |
| Halococcus sp. |
| Kazachastania khefir |
| Kazachstania aerobia |
| Kazachstania exigua |
| Kazachstania unispora |
| Kluyveromyces lactis |
| Kluyveromyces marxianus |
| Kluyveromyces marxianus var. lactis |
| Lachancea meyersii |
| Lactobacillaceae |
| Lactobacillus acidophilus |
| Lactobacillus amylovorus |
| Lactobacillus brevis |
| Lactobacillus buchneri |
| Lactobacillus casei |
| Lactobacillus casei ssp. pseudoplantarum |
| Lactobacillus crispatus |
| Lactobacillus delbrueckii ssp. bulgaricus |
| Lactobacillus helveticus |
| Lactobacillus kefir |
| Lactobacillus kefiranofaciens |
| Lactobacillus kefiranofaciens ssp. kefiranofaciens |
| Lactobacillus kefiranofaciens ssp. kefirgranum |
| Lactobacillus kefiri |
| Lactobacillus lactis |
| Lactobacillus lactis ssp. lactis |
| Lactobacillus parabuchneri |
| Lactobacillus paracasei |
| Lactobacillus parakefir |
| Lactobacillus parakefiri |
| Lactobacillus plantarum |
| Lactobacillus satsumensis |
| Lactobacillus sp. |
| Lactobacillus uvarum |
| Lactococcus cremoris |
| Lactococcus lactis |
| Lactococcus lactis ssp. cremoris |
| Lactococcus lactis ssp. lactis |
| Lactococcus lactis ssp. lactis biovar diacetylactis |
| Lactococcus sp. |
| Leuconostoc lactis |
| Leuconostoc mesenteroides |
| Leuconostoc paramesenteroides |
| Leuconostoc pseudomesenteroides |
| Leuconostoc sp. |
| Naumovozyma sp. |
| Pelomonas sp. |
| Pichia guilliermondii |
| Pichia kudriavzevii |
| Pseudomonas sp. |
| Saccharomyces cerevisiae. |
| Saccharomyces sp. |
| Saccharomyces turicensis |
| Saccharomyces unisporus |
| Saccharomycodes sp. |
| Shewanella sp. |
| Streptococcaceae |
| Streptococcus durans |
| Streptococcus sp |
| Streptococcus thermophilus |
| Weissella sp. |
| Zygosaccharomyces sp. |
Yogurt has fewer probiotic cultures which means it is not as robust. It does not do well fermented in different environments then it is used to. Yogurt which likes it warm won’t ferment if it is cooler. Yogurt which likes it at room temperature will over ferment or die at higher temperatures.
This does not mean that heritage yogurt cannot continue indefinitely like kefir grains it just means that they need more care.
Effects on the microbiome
Kefir is unique in the fermented milk family for being the only one which has been shown to provide probiotic strains which colonize the intestinal tract . This has many benefits for those who have digestive disorders such as:
- Reduction of pathogenic bacterial species
- An increase of beneficial bacterial species in the gut.
So far only a few of the probiotics found in kefir have been studied regarding colonization of the human gut so it may not be that the benefits found in the consumption of kefir rest solely on a few species but rather in the synergistic effect of the kefir as a whole.
Yogurt has not shown the same long term benefit for the recolonization of the human gut but that does not mean that it is of lesser importance for human health. Yogurt like any probiotic food helps to keep the gut balanced and healthy in a number of ways, including:
- Competing for energy with pathogenic bacterial species in the gut
- Altering the PH on the gut which negatively affects the growth of pathogenic bacteria
- Providing beneficial vitamins and enzymes which support your health
One factor in this comparison which has not been considered is that the yogurts which have been tested for their ability to colonize the human intestinal tract have all been done on commercial yogurt brands not heirloom types which have stable bacterial colonies. Since the number of bacterial species is higher than those of the commercial brands they may have colonization affects as well.
Alcohol content
In the kefir culture yeasts are in high number. The yeasts convert some of the sugar in the milk (lactose) into CO2 and alcohol. Although the amount is not enough to cause any concern it can get up to 2.5% with certain fermentation conditions. Some of the alcohol is used by the resident acidic acid bacteria which use it as energy but some remains in the kefir after it is strained and refrigerated. To learn how to reduce the amount of alcohol in your homemade kefir read Does Milk Kefir have Alcohol.
Yogurt does not have a high amount of yeast strains in the culture so most of the lactose is consumed by lactic acid bacteria. The byproducts of lactic acid respiration is lactic acid and CO2 which gives yogurt its tangy flavor.
Kefir is often second fermented whereas yogurt is not
Second fermentation means that the product is fermented once in the normal manner and then once it is finished the first fermentation another solid or liquid is added for another fermentation period. Most of the time this is done to add flavors to the ferment, carbonate it or to allow it to ferment for a long period of time without spoilage.
Kefir is regularly second fermented with fruit juices, coconut water and sweet vegetable juices like carrot or beet.
The method is simple:
- Once the kefir has fermented until the milk has thickened the kefir grains are strained out
- If you want carbonated kefir soda use bottles which are meant to hold pressure like swing top beer bottles
- If you just want to flavor the kefir you can use any bottle or jar
- Fill the container ¾ full of kefir
- Top up the container with your choice of flavoring
- For carbonated kefir soda put the lid on tightly
- For simply flavored kefir secure a cloth over the top with an elastic band
- Place the containers in a warm location for 12 – 24 hours
- Refrigerate and enjoy
Yogurt is not usually second fermented for two main reasons
- The main active culture in the yogurt is made up of lactic acid bacteria which tend to make the second fermentation unpleasant.
- Most second fermentations are to make carbonated drinks, mostly with the aid of yeast cultures which are not prevalent in yogurt.
The flavor differences
Kefir has a tangy flavor which comes from the lactic acid and acidic acid bacteria. The acidic acid becomes more active the longer the milk is fermented as the yeasts in the culture produce alcohol which the acidic acid bacteria use for energy. This can make kefir become almost too sour to drink and must be used for other things like baking, blended smoothies or cream cheese.
Yogurt has fewer bacterial strains in the culture which doesn’t include a strong presents of acidic acid. Most yogurt cultures are made up of predominantly lactic acid bacteria and the fermentation time is shorter which gives the LAB less time to acidify the milk. This makes the yogurt a milder, creamier flavor.
With or without oxygen
Kefir can be fermented with or without oxygen. This is because the number of bacterial strains in the kefir grain is high and they are varied in type. This makes them capable of using the lactose in the milk for energy with or without oxygen. Both lactic acid bacteria and yeasts can grow in an aerobic or an anaerobic environment.
It is the acidic acid bacteria which need oxygen so if the kefir is fermented in an anaerobic environment its growth is hindered, making the kefir less tart.
Yogurt is an anaerobic fermentation. The cultures which turn milk into yogurt are lactic acid bacteria which grow best in anaerobic environments.
As you can see there are several differences between kefir and yogurt but that does not make one better than the other.
Kefir has its uses as a tangy flavorful drink which can be used in smoothies, poured over cereal or just plain. It is healthful by adding probiotics to the diet which can improve gut health.
Yogurt is thicker so it is usually used as toppings for breakfast, mixed with fruit and made into thick sauces and dips. It also has live probiotics which can improve gut health.