Kefir Fermentation

How Long Does it Take Kefir to Ferment?

Generally, the time needed for kefir grains to complete fermentation can be determined by:

  • Microbial/culture activity of your kefir grains.
  • Grain-to-milk ratio.
  • Temperature.
  • How much lactose one intends to reduce in their kefir (longer fermentation = less lactose).
  • Type of kefir you want to prepare.
Kefir Fermentation

The optimum time for fermenting milk kefir is 24 hours at moderate room temperature of about 22°C with established kefir grains and that is when it should be strained. However, kefir can be fermented for shorter or a little longer period, depending on how you prefer your kefir including room temperature. The latter has a larger influence of how long it takes the kefir to be ready for straining. For best results regarding optimum quality, strain not too long after the milk has thickened and has a moderate sour taste, which should give good viscosity and a creamy texture. For the technical minded, when kefir reaches pH 4.5 indicates that it’s time to strain. If you strain let’s say 10 hours after the kefir has reached pH 4.5, over fermentation may result even though the kefir remains stable at about pH 4.5, which shall give variable results. Because of over fermentation, quite often and for most batches of kefir grains, a thin watery kefir with possibly a gritty mouth feel due to unfavourable curd texture formation may result. This is often the case during change of season, such as during autumn and spring, when the culture is trying to adapt to varying daily temperatures. However once temperature reach a reasonable stability the kefir should also become stable in regards to a smooth, creamy texture as apposed to a water thin gritty consistency.

Under certain conditions sourness increases while possibly taste, texture and consistency degrades the longer kefir is left to ferment with the grains. But this may not always be so, for there are many factors to consider that have an influence. Milk type and quality has much to do with this, where milk with lots of organisms already present, will give a different result compared to say, ultra heat treated or long life milk, which is 100% sterile which does not need to be refrigerated until the carton of UHT milk is opened. My experiments have shown that kefir made with freshly milked raw goat’s milk fermented for 24 hours produces kefir with a creamier texture, even during mid season such as autumn and spring.

NOTES For individuals interested in reducing lactose levels, kefir is best cultured for 24 hours with the grains, and then after strained the liquid-kefir is ripened in a separate container for some days before consumed.

What is the Best Temperature for Fermenting Kefir

The optimum temperature for making milk-kefir and water-kefir is 22°C or 71°F.

In a moderate to warm climate, kefir is cultured at room temperature. If room temperature reaches below about 16°C [61°F], then it’s probably best that the kefir is kept at a warmer temperature during fermentation. This is not 100% essential but anything below about 16°C means that the kefir will take longer to complete fermentation. You may also find that going from a high to lower temperature will result in a thinner kefir, until the grain’s microflora stabilizes at the low temperature over a week or 2. Generally, kefir can be cultured at extreme temperatures, ranging between 4°C to 30°C [39°F – 86°F]. However, the latter temperature figure should only be maintained over a short period, lasting no longer than 12 hours and then refresh the milk, or for 24 hours fermentation but for not longer than over 4 to 5 batches. Otherwise, if this high temperature is maintained over extensive 24 hours brewing cycles, the grains will degrade and begin to show signs of no growth or become mushy in texture somewhat like cheddar cheese when squeezing a grain between two fingers and eventually disintegrate and shall no longer grow.

in the sun when the sun was shining during the day or hung near a fireplace. I believe that the freshly obtained milk was relatively warm when added to the grains in the leather bag, and such bags kept milk warm for some time. So keeping the bag in the sun or near a fireplace, would keep the milk at an average of 22°C. The best kefir is thus produced at around that temperature because over many centuries the organisms of kefir grains have evolved and well adapted at that temperature.

NOTES The colder the temperature the longer it takes to ferment kefir, while kefir cultures more quickly under warmer conditions. Also, kefir cultured at very low temperatures for a length of time, inhibits or slows down the growth of certain strains of organisms over other strains. As an example, acetic acid bacteria proliferate under colder conditions in comparison to lactic acid bacteria, except for Bifidobacterium psychraerophilum [ from the Greek words psychro meaning cold loving and aero meaning air loving], which can are viable and reproduce at temperatures as low as 4°C. Certain strains of organisms may be reduced in numbers from the grain’s microflora over other strains or genus group. Fermenting above 40°C [104°F] for longer than a few days, will have an adverse effect on the grain’s growth factor. This is due to inhibition of enzyme activity of organisms at that temperature and beyond, which effects their ability to survive and reproduce.

In a tropical climate, kefir grains may suffer and not increase very well due to ongoing excessive heat. With temperatures above 28°C [82°F], it is advisable to culture your kefir in the fridge during the day, and then transfer the container to room temperature in the evening to set the kefir overnight, making it ready for straining in the morning. Another idea is to use an icebox, putting an ice pack in the icebox along with the kefir fermenting jar. Use 2 ice packs, keeping one in the freezer while the other is kept in the icebox, then alternate the ice packs when the one in the icebox thaws and becomes warm..

I find that during extensive hot spells during our dry hot summer months here is South Australia, after a given period, the overall size per each grain becomes small, like the size of cooked white rice. The grains self-propagate or self-seed as smaller bodies happening over a short period, and the texture of each grain becomes soft or mushy which easily breaks apart when squeezed between two fingers. The grains lose the more firm, rubbery texture that they have when cultured in cooler conditions during winter months. However, this doesn’t seem to cause any problem for the mother-culture, if the temperature is maintained below 28°C [82°F] and the milk is changed daily while making sure that the grains are not overcrowded by halving the volume of grains every 5 days. As cooler conditions arrive in winter, the grains should grow larger with a firm rubbery texture once again if the room temperature is in the range of 19°C to 23°C [66°F to 73°F].