The process of making Homemade Yoghurt Cheese. Hanging the cheese. You can massage the cheese from time to time to make it lose liquid faster. (Mette Randem/FTWP)

While I lean back and do nothing, millions of bacteria are multiplying in my kitchen. They will continue for hours, long after I have gone to bed.

Normally, the words “kitchen” and “bacteria” don’t go so well together. But although the proliferation of bacteria is hardly an ideal scenario in most cooking operations, it is crucial for making one of my favorite ingredients, the staple of our family breakfast. In the morning, the bowl of milk I fed to the bacteria will still be warm to the touch, and its contents will have transformed into yogurt.

I eat yogurt for one main reason: I like it. I like the smooth texture, the refreshing ever-so-sour taste combined with my homemade raspberry jam, and the fact that it allows me to eat without cooking or resorting to bread. (And I appreciate the fact that my kids will eat it, too, without much fuss, leaving me to meet the new day with a newspaper and relative quiet.)

Yogurt has been around for centuries, if not millennia. It most probably originated as an accident; according to legend, somewhere in Central Asia. Milk left out overnight was attacked by naturally occurring bacteria, and the result not only tasted good but kept well. Having been assailed and partially eaten by good-natured bacteria, yogurt was much less likely to become the target of other, harmful ones. It had one additional advantage: a much lower lactose content — the milk sugars are mainly what the bacteria eat — that made it much easier for humans to digest. (Lactose intolerance is far more common among Asians than among Europeans.)

The use of benign bacteria is one of the triumphs of cooking, an introduction of culture into a world where fire had been considered the only way to make food safe. Much like breadmaking, this ancient craft hasn’t been fully understood until quite recently.

Yogurt is the result of a chemical miracle conducted principally by two bacteria. Streptococcus thermophilus, bacteria that love warmth (and don’t leave behind harmful spores), work with Lactobacillus bulgaricus to transform lactose to lactic acid. As the milk’s pH lowers, its proteins coagulate, creating yogurt’s creamy texture.

Even though yogurt probably originated in Asia, the world’s yogurt belt stretches from Northern Africa up through Greece and parts of Eastern Europe and east through the Caucasus to the Indian subcontinent. Yogurt lovers in those parts of the world use it for all kinds of purposes, including sauces, marinades and cheeses. While consumption in the United States still lags far behind that of Europe, popularity has been growing; U.S. sales of refrigerated yogurt rose by 55 percent between 2005 and 2010, according to the research firm Mintel.

I started to make my own yogurt a few years ago. At first I was curious whether it could be done without such special equipment as a yogurt maker. Luckily, the level of precision required at entry level is not high, especially if you don’t mind if the results vary. The only things you need, really, are clean kitchen equipment and a starter culture. This starter can be bought from specialist cheese-making shops or found in other plain yogurts.

I inoculate my milk with a few tablespoons of my last successful homemade yogurt or, more often, with the best candidate I can find in the store, preferably organic. Because most yogurt is made using the same bacteria culture, the only thing I make sure of is that it does not contain starch or modified starch. (Some types of commercial yogurt are really nothing more than thickened milk with yogurt flavor.) Whenever I can, I make my own yogurt, using milk from a local farmer who sells me fresh, organic, non-homogenized and unpasteurized milk that I heat to 175 degrees to kill off unwanted germs.

I cannot claim that my yogurt is the best I have ever tasted; in France I am always struck by the delicate balance and fine nuances of farm-made yogurt from Normandy, where naturally occurring bacteria add to the complexity of flavor and centuries of craftsmanship ensure a delicate and well-controlled process. But my yogurt is far better than the commercial stuff I resort to otherwise. And although the variable results would be a drawback if I were to sell it, they make the home process all the more charming. I like to think I can taste the difference between yogurt made from milk from a cow that has been on a summer pasture and that from one on a winter pasture, and even between yogurt made on a cold and rainy or a warm and sunny day, although the temperature of the milk when I mix in the starter and the climate in the kitchen probably are more important.

Whenever I make a lot of yogurt, I use the surplus — whatever I do not expect to eat within a few days — to make cheese, from the simplest cream cheese to interesting four-day cheeses that are firm on the outside and creamy on the inside, with a texture almost like that of buffalo mozzarella or burrata. Although real cheesemaking demands the careful application of different bacteria cultures and rennet, plus equally careful control of temperature, fat content and storage, I find it fascinating what you can achieve with just yogurt and cheesecloth.

The more yogurt I leave to hang in one single piece of cheesecloth (or in a kitchen towel), the bigger difference there will be between the texture on the inside and the outside. Adding herbs allows me to make use of my garden and to explore combinations of flavors even those millions of bacteria can’t manage to create.


Homemade Yogurt

Yogurt Cheese

This is Viestad’s last Gastronomer column for the Food section, but he will continue to write occasional pieces.