Almost all the butter Animal Farm makes is bought by Thomas Keller to serve in his top-flight restaurants, the French Laundry and Per Se. Each year, a small amount is sold to the public via New York’s Saxelby Cheesemongers, where it’s snapped up fast—even at premium price. And understandably: Each little knob of the stuff is radiantly yellow and delicately fragrant. Spread on bread, it’s cool, rich, and unusually complex in flavor, with a lingering nutty nuance.
The butter from New York’s Ronnybrook Farm, which doesn’t go through the culturing step, is delicious in a different way—paler and firmer, with a clean, milky taste that remains on the palate for minutes on end. What makes these butters so different from each other, and so much better than the sticks you get in the supermarket?
“Especially for sweet cream butter [that is, butter that’s not cultured], you want the cream to be as fresh as possible,” says food scholar and author Harold McGee. As cream spends time outside the cow, it undergoes a number of changes. Tiny air bubbles that get into the milk during processing and transportation, as well as changes in temperature, disrupt some of the fat. globules and make them clump. Enzymes, both those naturally present in milk and those created by bacteria that grow at low temperatures, start to break down some of the milk fat, which can cause subtle off-flavors, as can the presence of oxygen.
And these changes are magnified when cream is concentrated into butter.
Much of the lush nuance of farmstead butter is due not just to the cows’ excellent diets of grasses and flowers, but to the seasonal variability of those diets. “In late summer, with lusher grass and more flowers, there’s more intense flavor, and the texture is much more spreadable,” says St. Clair. The hay the Animal Farm cows eat in the winter is no less carefully assembled: “clover, second-cut grasses, trefoil—and terroir. If I fed a herd the same things in California, the butter would taste completely different.”
When cows are raised on a fixed diet, the cream tastes the same year-round. And a lot of consumers, and therefore producers, prize this consistency. As a result, even many artisanal butter producers buy cream in bulk from creameries that batch together the output of numerous farms and mechanically separate the cream.
Historically, culturing wasn’t something you did to make your butter better—it was just what happened. If you were a farmer with a cow or two, it’s likely you needed a few days’ worth of cow’s milk to amass enough cream for a batch of butter. As your bucket of cream sat around, waiting in vain for refrigeration to be invented, wild bacteria naturally found their way into it and soured it a bit.
Nowadays, culturing cream is a careful science. Elaine Khosrova, author of the recent book Butter: A Rich History, showed me how she makes butter in her home kitchen, starting with a powdered culture of freeze-dried bacteria made by Danish biotech company Chr. Hansen. The culture contains a precise mix of four different strains of bacteria. Two strains are primarily responsible for creating lactic acid, which gives a tart flavor and lowers the pH of the cream.
As the cream becomes more acidic, the other two strains start to create new aroma compounds; most importantly diacetyl, which is the molecule responsible for what we think of as buttery flavor. Synthesized diacetyl is added commercially to a wide variety of foods—margarine, microwave popcorn, pancake syrup. In the supermarket, it’s increasingly possible to find cultured butters, but commonly, industrially made butter is not cultured. Instead, it has diacetyl added after the fact, to give it the desired aroma. Diacetyl is also produced during fermentation of wine, especially buttery-tasting Chardonnays, and beer, where it’s usually considered undesirable.
Meanwhile, in the now-acidic cream, some of the strands of protein that make up the fat globules’ membranes slowly split off and knit together into microscopic webs throughout the cream, causing the liquid to thicken. The disruption of the membranes also means there’s more free fat floating around and clumping together.
Apart from the magic of witnessing the process firsthand, the main compelling reasons to make butter at home are if you have access to excellent cream or “a really interesting culture,” says McGee. Store-bought buttermilk—which is mostly made by culturing low-fat milk, not as a by-product of butter making—has the right kind of culture for making homemade butter, so it can be a good starting point.
Only a few butter makers culture longer than 48 hours, but long culturing can produce unique, delicious effects, as the bacteria work their flavorful wonders for days. Grant Harrington of England’s & [Ampersand] Butter lets his cream culture for a full week to make it “as buttery as possible.”
Elaine Khosrova has traveled the world tasting butters, and she gave me tastes of a selection of butters that varied widely not just in taste but also in consistency. “The aspect I’m most interested in these days is texture,” she says. She cut a long, thin slice from a block of French butter and held it up by one end. It was firm yet smoothly bendable, and its yellow surface was shiny and dry. “There’s a lot of moisture in it, but it’s all tucked away in tiny droplets.” We ate the slice. It was delicious.
The texture of butter is mostly a factor of the solid fat crystals that make up its framework. Nestled within the matrix of crystals are bubbles of water, milk solids (mostly protein and sugar), air, and noncrystallized fat.
The majority of the fat in butter is part of that crystalline network, but fat globules that survive churning intact, still snug in their membranes, don’t link up with the crystals. As a result, they don’t contribute to the butter’s firmness, so all else being equal, the more intact globules are in the butter, the softer it is.
Both St. Clair and Rick Osofsky, president of Ronnybrook, emphasize how gently they treat their cream so as to keep the fat globules intact. St. Clair ladles the cream layer off the milk by hand as it slowly rises, and Osofsky keeps all his milk unhomogenized, so even the bottles of Ronnybrook milk for sale in supermarkets have a layer of cream at the top.
The ratio of harder to softer fatty acids in the cream is also a major contributor to texture. Corn-fed cattle give milk with more palmitic acid, a fatty acid that’s solid at room temperature. A diet of grass leads to much more oleic acid, which is unsaturated, and hence liquid at room temperature. When cows are pastured, as St. Clair points out, the summertime milk tends to have a higher proportion of softer fats. The more of the unsaturated fat that’s present in the cream, the softer the butter will be.
The churning method—fast, slow, how much water comes out—and the way the cream was stored prior to churning, also affect texture.
Robert L. Bradley, professor emeritus at the University of Wisconsin-Madison, notes in his technical butter maker’s manual Better Butter that spreadability of butter out of the refrigerator is a surmountable issue. “Considerable research has focused on ideal spreadability . . . The quick fix is to leave butter at room temperature for 2 hours. Mission accomplished!”