Kefir is a complex fermented product very similar to drinkable yogurt. Unlike yogurt, the fermentation process is incredibly vigorous and strong enough to not need sterilization, works best at room temperature, and doesn’t require much care at all: you can pretty much drop “kefir grains” into a glass of milk, cover it with a sheet of paper, and have kefir after a day or two…it’s truly that simple.
It results in tangy liquid drink and is probably the most potent probiotic you can add to your diet. I use substantial amounts in my daily breakfast smoothie.
What is kefir, besides something that’s nearly identical to drinkable yogurt? It’s a diverse group of of bacteria, fungus, and yeast species that over time form a biofilm colony we call “kefir grains”. With varying conditions, different organisms may “come out ahead” slightly but in general at room temperature and with milk as the food source, the end product of their cohabitation is the fermented food we call kefir.  If you’re the type who likes to read, this is probably the single best reference available on the internet for learning about “what is kefir”: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626640/ (mirror: fmicb-06-01177)
While folks use a lot of different things to make kefir from (such as A2 milk), I use organic whole milk myself:Â I find it created a very rich and satisfying kefir.
When starting up production with a freshly acquired set of grains, it’s customary to get the grains back up to speed by discarding the first few batches. This allows the ecosystem to stabilize and acclimate to your local environment.
Grain to milk ratio of 1:4 usually works well around room temperatures and a 2 day fermentation cycle, but every situation (and desired outcome) is different.
Longer fermentation makes a more tangy kefir, and less time seems to make a cheese flavor more pronounced. Experiment and find what works best for you: taste the spoon after each stirring to get used to the flavors that develop, and how long that flavor takes.
Usually stir it three times: briefly when the fresh material is added, briefly after 24 hours, and briefly right before straining the grains out for the next batch.
As things ferment, solids and water will begin to separate. I find it’s a good reminder to stir when I see this:
If you don’t stir it at all for a few days and don’t keep it in the fridge, it can get an orange-ish discoloration on top which seems to be some relatively harmless organism (likely an airborne bacteria.) You can feel free to skim it off the top and then stir things back up again…I may occasionally simply stir this directly in and try not to think about it too much…
To separate the grains from the kefir, first stir briefly, then place a fine strainer in the plastic container, then a coarse strainer in the fine strainer, and finally pour the fermentation vessel contents in.
Use a spoon to move things around and start gently separating things.
Finally scoop the grains into a new clean glass jar.
In the fine strainer, you’ll often have things that don’t go through into the finished product.  You can eat it directly, add it to the finished kefir, or add it back into the fermentation vessel. I’m not sure if they’re free-floating proto-colonies, an independent bacteria but they taste like fresh yummy cheese.
Makes sure your fermentation vessel doesn’t seal tight (I removed a plastic seal from mine.)Â If you use a ball jar, replacing the metal lid with a paper towel works nicely.
Put a lid on the container and stick it in the fridge. Regarding storage, it’s usually safe to keep strained kefir in the fridge for up to a month…I keep mine in covered containers and that seems to seal things in nicely. I’ve read some folks end up getting mold on the top, so if that happens throw out that specific batch (never seen it myself.) Â
It will separate a little if it sits untouched for a while, just stir to blend it again.
It’s nearly impossible to screw up. Just keep things reasonably clean while you’re working, no cross contamination, and that’s 99% of it.
Eventually, you’ll have too many grains: they’ll take up a lot of space in your fermentation vessel, and they’ll start making kefir faster than you can drink it! While you can compost or flush the excess grains, I’d recommend you try to find a health-conscious friend who’s interested in adding some fresh homemade fermented foods to their diet!
Light additional reading:
