producing kefir grains from commercial kefir?

The dynamics of the Grain growth are not currently well understood, much less its formation. Some researchers attempted to create grains in laboratory, but failed.

There are over thirty or fourty strains of microbes in the kefir, and their ecological relationships are very complex. One could call the whole kefir culture an ecosystem of its own.

The grains grow either because the matrixes of existing grains entice the microbes to create more grain matrix, or because there are specialized microorganisms inside the grain that are responsible for creating more grain.

What is known is that the grains need Kefiran to grow, and Kefiran needs Alcohol in its synthesis. Commercial cultures of kefir often omit the alcohol-creating yeast for obvious reasons, so it too adds to the impossibility of getting Kefir grains from commercial kefir.

Either way, the fact is there grains do not come into being on their own. New grains are split from existing grains.

There is a small possibility that a kefir culture from grains that was strained could form new grains, but its not confirmed.

The commercial cultures are sold with around five to ten strains, much less than full blown kefir grains. They won't form grains, since the strains were hand-picked in lab by their function, and probably the grain-forming ones were left out.

Store bought kefir is made with a powder and thus will not produce grains. When you are making kefir (milk or water) at home the product is quite different as you actually have to strain the grains out. I've had much better experience with water kefir than milk kefir (with respect to grain reproduction).

I have successfully produced kefir grains from about a teaspoon of dried commercial kefir from Ukraine. It was just dried on a cloth for a week or so of transit and then carefully rinsed out again with milk. It took a few weeks of adding more milk and sieving off every couple of days to get there.

Over the last year though, my grains haven't expanded much so I'm not sure if I've figured out the optimum conditions for grain growth. The nature of the grains has become more yellow. When I first grew grains they were white.

One strain I have produces a thick cottage cheese consistency and cheesy taste kefir, especially if I tip off the whey and feed it with another batch of milk before straining it.