I have a friend who claims that regular consumption of kefir will provide her with a long, healthy, disease-free life. I hope she's right.
It seems that most kefir enthusiasts drink it for the health benefits (which are substantial) but almost apologetically claim that the flavor is an acquired one. Sure, if you're not open to the taste of sour milk, kefir can be offputting. But, by making it yourself, you can control the degree of sourness— from mildly tangy to sharp and effervescent.
For the uninitiated, kefir is fermented milk, cultured with kefir grains. The gelatinous grains are a matrix of sugar, protein, fat, and ash that harbor a garden of yeast and bacteria. It is the yeast that sets it apart from other milk cultures that are predominately bacteria.
Making kefir is as simple as adding the grains to milk (about 1 tablespoon of grains per 2 cups of milk) and allowing it to ferment at room temperature for a day or two. When the desired texture and flavor are achieved, the grains are strained from the kefir and recycled to start a new batch. If those directions sound vague, they are intentionally so. Even with careful weighing and control of temperature, the results are not always consistent. I've come to believe that this is because kefir grains are living organisms that operate with dual microbes and that the speed and efficiency with which they culture a new batch of kefir is largely dependent on their active state at the time of introduction. For example, I've found that after straining the grains from a completed batch of kefir and immediately adding them to fresh milk, fermentation (detected by the onset of a sour flavor) begins more rapidly than when a batch is started with grains that have been stored in the refrigerator between batches.
With so many variables, I no longer bother with weights and temperature, I just set it out on the counter and let it do its thing. Sometimes I catch it when it turns creamy and just begins to acquire a tang. Sometimes I let it ripen until it curdles and precipitates whey, at which point the curds can be drained to form a soft, tangy cheese. My favorite thing is to cover it tightly while it ferments to trap the CO2 released by the yeast until it gets fizzy. Milk champagne is a wonderous thing!