A few months ago a friend of mine gave me just over a teaspoon of kefir grains. I have practiced several different forms of fermentation over the past several years. I've made home made sour cream, yogurt, kombucha, and kim chee. I can honestly say that kefir is the easiest and most dynamically useful fermentation that I have played with. It is also the easiest. As I just gave some kefir grains to some other friends I thought it would be worth while to writeup my process for creating kefir, and the various ways that I process it.
First a teaspoon of kefir grains is enough to culture about a cup of milk over the course of a couple days. If you use warm milk the process goes more quickly, but the kefir grains and milk can both be cold when you combine them, and everything will still culture correctly. The culture needs to breath while it is cultivating. To accomplish this I culture my kefir in a mason jar with a 2 layers of cheesecloth held in place by a mason jar ring. However, the friend who first gave me his culture just left the lid loose on his kefir jars and never ran into any problems. After a day you will want to taste your kefir to see if it is as sour as you would like it. When the culture tastes how you would like it to taste then you strain out the grains. I generally put the grains back into the mason jar that I did the culturing in, replace the cheesecloth with a normal lid and put the culture in the fridge till I am ready to use it again. The culture is very hearty and I haven't had any problems leaving it for a week or longer between cultures. Every few batches I rinse the grains off to avoid too much milky solid buildup.
If you let the culture go long enough it will become a full yogurt consistency at which point the curd will separate from the whey of the kefir. This isn't necessarily a problem, and I often strain the whey for use in other products such as bread. However, when you have a thick product it is difficult to get the kefir grains out without damaging them. I take a fine mesh strainer and put the liquid in to it and then take a spoon or butter knife and run it sideways across the bottom of the strainer. It's important to keep the side of the spoon vertical as opposed to angled so you don't push the grains down into the strainer making your product lumpy, and damaging the culture. If you do this regularly it will breakup your grains, but as long as they aren't actually pushed through the strainer it won't cause any problems with future batches.
That is a basic rundown of how I make kefir. It's nearly impossible to messup a batch. The worst you can do is let it go "too long" and have it fully separate when you wanted a lightly sour smooth batch. It's still a wonderful product, just a little different. Kefir can stand in for buttermilk in all of it's uses. I've used kefir to make buttermilk biscuits, pancakes, and even as a base culture for sour cream. The sour cream turns out a bit less nutty and a bit more yogurt like than when you use buttermilk, but it still works in pretty much all the same ways. I've also strained the whey as a I said above and used it to make bread. If you get a particularaly thick batch it eats almost exactly like yogurt. We got through a ridiculous amount of kefir every week in my house, and I highly recommend this to anyone who's up for making some. As I just gave out some culture it will be a little while before I have more to spare, but I'm sure I'll be able to give some away in a couple weeks.