I am a fan of kitchen bacteria -- the kind that ferments milk.

With its help, I can make my own tart yogurt, zingy kefir and dense, tangy crème fraîche.

I first discovered bacteria's prowess when I learned to make yogurt about 35 years ago, setting it on a sunny window in my dorm room. The yogurt maker I later got as a wedding gift did not work as well as the top of our first refrigerator did when I set out those nice glass jars with their snap-on tops.

These days, my own college-age kids whir homemade yogurt into protein shakes. One son prefers kefir (pronounced keh-FEER) blended with fruit sorbet into a cooling summer drink. I use crème fraîche (krehm FRESH) in lieu of sour cream, make light fluffy pancakes with kefir, and marinate chicken and turkey in yogurt before roasting. It tenderizes the meat and creates a lovely mahogany skin. I guess you could say we are into culture.

Making these fermented milk products is easy and satisfying. They taste better than anything you can buy in the store. Many commercial yogurts contain stabilizers and sweeteners, and the plain "all natural" varieties are often sour-tasting or bitter. Plus, these homemade products are far less expensive than any you can buy.

The primary difference between yogurt and kefir is their bacteria. Kefir contains more bacteria, and its flavor is a bit more complex than yogurt's. Crème fraîche is simply cultured full-fat cream. All of them work wonders in baked goods and marinades.

These fermented milk products are good for you, too. Their probiotic lactic-acid bacteria promote good digestion. They are loaded with the nutrients that combat fatigue and strengthen the immune system. All I know is that I feel a burst of energy when I knock back a cold glass of kefir on a hot day. It's creamy, soothing and refreshing.

I have to admit to a childlike enthusiasm for the miracle of fermentation. To make yogurt, kefir and crème fraîche, all you need is a "starter" and some milk or cream. There are commercial starters on the market and these yield predictably satisfying results. Or you can use unsweetened yogurt, kefir or buttermilk to get things going, reserving a little of the finished product for the next batch.

To thicken yogurt, put it into a cheesecloth-lined strainer to help drain off the watery whey. Refrigerate the strained yogurt (the whey makes a delicious cold drink sweetened with honey or sugar, but it does not keep, so discard if you're not drinking it within a day).

Whether making yogurt, kefir or crème fraîche, the first step is to heat the milk or cream to between 180 and 190 degrees, or to the point that it's steaming and beginning to form bubbles. The heat alters the milk's whey proteins and helps create denser consistency. Then let it cool to about 115 to 120 degrees (very warm) before introducing the starter. (If it's too hot it will kill the beneficial bacteria; if not hot enough, it will be slow getting started.)

Here are three basic recipes plus several ideas for creating great cultures. I prefer using the pasteurized (rather than ultra-pasteurized) varieties of milk or cream because of its taste, and I find that the pasteurized seems to work better in these preparations.

Beth Dooley is a Minneapolis writer and cooking teacher.