RIGHT now my kitchen is teeming with bacteria, and I’m doing everything I can to make them feel at home. They’re lactic acid bacteria, the ones that ferment milk into yogurt and buttermilk, cream into crème fraîche. I’ve been making all of these, as well as milk thickened with reputedly beneficial “probiotic” lactic acid bacteria. And getting to know viili, a Finnish fermented milk that reminds me of the Japanese soy product natto. It’s slithery.
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Evan Sung for The New York Times
WHAT FAT GLOBULES CAN DO Make your own yogurt, then experiment with it.
I’ve made my own yogurt nearly every week for more than 10 years, beginning with a starter given to me by a friend from yogurt-loving India, and using the last spoonfuls of one batch to make the next. It’s a satisfying ritual of continuity and caretaking. And the yogurt is less expensive and better than anything I can buy. It’s free of stabilizers, sweeteners and waterlogged fruit, and it’s fresh tasting and tart, not sour. I start every day with a bowl of it.
Even if cultured dairy products aren’t part of your daily regimen, they’re worth making once in a while just to know how good they can be, and to experience the everyday miracle of fermentation. You stir a little starter into warm milk or cream, let it sit, and in a few hours the bacteria have multiplied a hundredfold and created a tart, aromatic, thickened mass, with many billions of bacteria in every spoonful.
A growing number of studies have found that some lactic acid bacteria do seem to offer health benefits, supporting the lore of traditional dairying cultures. The lactic acid bacteria are a group of microbes that share the ability to convert sugars into lactic acid, which suppresses the growth of their competitors. The lactic acid also causes the proteins and fat globules in milk to cluster into a continuous solid network, with the milk’s water trapped in its pores.
The protein-fat network is fragile — it’s holding 25 times its weight in liquid — so the watery whey gradually leaks from it. This is why whey pools up in the yogurt container after you scoop out the first spoonful, and why manufacturers add stabilizers.
Much less whey drains out of yogurt made from certain strains of lactic acid bacteria that can convert sugars into long starch-like molecules. These exopolysaccharides, or EPS, bind to the water and one another and make the whey less runny, thicker and more clingy.
EPS producers are the bacteria that dominate in Finnish viili, which is so clingy that you can stretch it a foot or more between bowl and lifted spoon. You eat viili by cutting it into pieces.
To make yogurt, first choose your starter yogurt. If no one offers you an heirloom, I recommend one of the ubiquitous global brands, sweeteners and stabilizers included. They tend to have very active bacterial cultures, including EPS producers, and the additives end up diluted to insignificant levels. Delicious specialty yogurts make less predictable starters.
Then choose your milk. I prefer the flavor and consistency of yogurt made from whole milk. Many types of reduced-fat milk replace the fat with milk solids, including acid-producing lactose, and make a harsher tasting yogurt. Soy milk sets into a custardy curd that becomes very thin when stirred.
Heat the fresh milk at 180 to 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 a finer, denser consistency.
Let the milk cool to around 115 to 120 degrees, somewhere between very warm and hot. For each quart of milk, stir in two tablespoons of yogurt, either store-bought or from your last batch, thinning it first with a little of the milk.
Then put the milk in a warm jar or container or an insulated bottle, cover it, and keep the milk still and warm until it sets, usually in about four hours. I simply swaddle my quart jar in several kitchen towels. You can also put the container in an oven with the light bulb on.
Once the yogurt sets, refrigerate it to firm its structure and slow the continuing acid production. To make a thick Greek-style yogurt, spoon it into a fine-mesh strainer or colander lined with cheesecloth, and let the whey and its lactic acid drain into a bowl for several hours. (Don’t discard the whey, whose yellow-green tint comes from riboflavin. It makes a refreshing cool drink, touched up with a little sugar or salt.)
What can you do with yogurt beyond enjoying it as is? I use it to make especially tender pancakes and waffles, and in desserts, including a soft-frozen yogurt, barely sweetened. It’s also fun to explore the unusual soups and salads and sauces and drinks and sweets made in the yogurt belt from the Balkans through Central Asia to India.
You can use the basic yogurt method to make versions of any cultured dairy product, provided your starter carries live bacteria. You can ferment cream with yogurt, or make a yogurt variant by adding buttermilk or a probiotic-drink to milk. You can combine starters and blend the apple-freshness of yogurt with the butteriness of buttermilk.
Crème fraîche is trickier to make than yogurt. Commercial versions vary a lot, with flavors from creamy to buttery to cheesy, colors from pure white to golden, some of them stable enough to boil and others oily from the beginning. None that I’ve found makes a good starter. Use buttermilk instead, stirring it into heavy cream. The cream will set faster and firmer if you preheat it and keep it warm as you do the milk for yogurt.
Heavy whipping cream comes in two main forms: one cream-colored, pasteurized and unhomogenized, the other white, ultra-pasteurized, homogenized, and stabilized with gums. The first has better flavor but tends to separate into thick and thin layers during the hours it takes to ferment, and is more likely to leak butterfat when heated.
If you’re going to cook with the crème fraîche or blend it with other flavors, then stable homogenized cream will do. If you’re making crème fraîche simply to top fruits or pastries, then seek unhomogenized cream.
And if you haven’t tasted it, try the combination that Eric Ziebold, the chef of CityZen in Washington, introduced me to: crème fraîche and french fries. Like sour cream on a baked potato, but even better.
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