Milk (42 page)

Spoon out a little and taste it, being careful not to burn yourself. The lightly browned fat will be still oilier than the batch you tasted at melting point. But the tiny brown scintillas will have a nutty sweetness unlike anything you’ve encountered in the earlier samples. Let it solidify at room temperature and taste it before briefly chilling it in the refrigerator and tasting it again. Both times you will find the texture still less whole—that is, grainier, more congealed, less waxy, and further from melt-in-the-mouth suavity—than the barely melted sample you tried before. And the browned bits will just reinforce the nonbutteriness, or ex-butteriness, of the flavor.

And now for something completely different: Take the fourth piece of butter and put it in a small lidded container. Find a good strong-tasting onion, cut
off a slice, and put it in with the butter. Cover the container tightly and return it to the refrigerator for a day (or until you next remember it). Remove the lid and take out the onion before smelling and tasting the butter. It will have acquired a distinct onioniness that will remain until the end of its existence. The onion, on the other hand, won’t be in the least buttery.

You have now proved something known to everyone who works with dairy products: No other food you can name exists in a state of more fragile chemical equilibrium—translating into flavor equilibrium—than butter and the
milkfat from which it is made. The old superstitions about butter spoiling or not “coming” if somebody merely looked at it the wrong way aren’t far off the mark. It can hardly sit still for a minute without risking intervention from the universe at large. The agents of drastic, irreversible change are all around milkfat as soon as it is removed from the rest of the milk and chemically turned inside out by some form of churning. And the same is true whether the milk comes from a cow, goat, sheep, buffalo, or other animal.

Some of the potential changes are delightful, some ghastly. They would not occur if the chemist’s laboratory of the
rumen and the finishing shop of the udder did not direct thousands of different substances into the milkfat, over and above those that go into the much less complex casein and whey. Butter is made up of so many components that some probably still don’t have names. The slightest shift in balance can mean an immense flavor difference. This incredible delicacy reflects the life-giving importance of milk itself.

Milkfat is the most concentrated source of energy for nurslings. And it is the crux of their first taste experience. As cooks know, fat is the soul of taste. Vegetable fats like olive or walnut oil impart their unmistakable note to anything cooked in them. But when it comes to milkfat—“butterfat” in its pre-butter state—flavor also plays a biological role. Every species of mammal, from mouse to rhinoceros, produces milk with a “lipid profile,” or mixture of fat components, peculiar to itself and not to be confused with any other creature’s milkfat. This species-to-species variation in the flavor palette of milkfat is the strongest marker by which newborns instinctively
recognize the milk of their own kind.

Divert milk into the outside world, and all the intricacies of milkfat have a new theater in which to operate. It’s a subject to defeat even textbooks of dairy chemistry, which always acknowledge that much remains to be discovered about such-and-such aspects of milkfat. The only aspects I will touch on, as the ones most related to flavor, are globule membranes, fatty-acid content, and true buttermilk.

Milkfat exists in milk as tiny globules surrounded by delicate but surprisingly
strong membranes whose composition is still not fully understood because even trying to study them under a microscope distorts their structure. To an extent, the membranes protect the globule contents—a soup of different
fatty acids, together with other fat-related substances too complicated to discuss here—against attack by outside forces.

You can think of the membranes as something like the film around soap bubbles, except that they have a much more complex architecture, with microscopically thin outer and inner layers comprising intricate mixtures of fat-related substances and numerous enzymes. If you have tried the mini-experiment in buttermaking at the start of this book, or whipped some cream by the directions on
this page
, you have explored one way to knock apart the many substances making up the globule membrane—releasing flavors that would not register as clearly otherwise—while also letting the enclosed fat flow out of the former “bubble.”

There are other conditions under which the membrane can be breached and the contents spilled out, but usually with nastier or at least trickier results. Handle milk, cream, or butter without an eye to sanitation, and eventually you will invite certain
bacteria or enzymes that dismantle fat globules, releasing the hideously penetrating flavors of
rancidity. “
Lipolysis,” or breakdown of fat, is the technical name. But curiously enough, small amounts of controlled lipolytic action are exactly what’s needed to produce the bracing sting of several excellent Italian cheeses—just one instance of the truth that harnessing the flavor potential of milkfat takes exceeding skill and experience.

The next culinary dimension of milkfat that cooks need to know something about is what kinds of fatty acids it contains. Here I must gloss over many niceties of technical definition to explain that any edible fat in our kitchens, from peanut oil to rendered lard, basically consists of compounds properly called “
triglycerides.” The last three syllables reflect the fact that they all involve a molecule of an alcohol known as “glycerol,” which is reponsible for the basic effect of suave fattiness in fats. The “tri” part means that they all contain three fatty-acid molecules tacked on to the glycerol like three pennants waving from a pole. The truly dizzying aspects of the picture are first, that fatty acids come in phenomenal numbers of different configurations; second, that any triglyceride molecule can contain a mix-and-match assortment of any three fatty acids from the whole spectrum; and third,
that all the resulting permutations and combinations will taste different.

Most of the vegetable oils used in cooking contain at least dozens of individual fatty acids. But by comparison, the fat in
cows’ milk is now known to have more than four hundred, shuffled like cards in a deck to furnish the different “tri’s” in thousands of triglycerides. Undoubtedly, milkfat from other animals is equally complex. But the unique commercial importance of cows’ milk means that it’s been better studied than any of the others.

There are several ways to distinguish different kinds of fatty acids. Most are beyond the scope of a book like this. Those important enough for cooks and consumers to warrant brief explanations start with volatility, or the tendency to evaporate at fairly low temperatures. Heat a bit of butter barely above lukewarm and, as you have just seen, the more volatile fatty acids will vanish in a puff of fragrance, never to be recovered.

Individual members of the fatty-acid tribe are also often grouped under the rubrics “short chain,” “medium chain,” and “long chain,” referring to the actual length of the molecule as measured by counting basic architectural units. These units consist of carbon atoms—in most cases from four to twenty-two—linked with one another in arrangements that can be very crudely visualized as daisy chains with many odd twists and turns in three-dimensional space. Every carbon atom on the chain has hydrogen atoms attached, but here a whole cluster of variables occurs. Each carbon atom could potentially link up with two hydrogen atoms via straightforward connections called “single bonds.” When every one actually is so linked, the fatty acid is said to be “saturated,” meaning that all potential vacancies for hydrogen are filled. If, however, some are linked with only one hydrogen atom apiece by more tricky and unstable connections (“double bonds”), there are unfilled vacancies and the molecule is said to be “unsaturated.”

For about half a century Americans have been absorbing news bulletins about the qualities of saturated and un
saturated fatty acids; at times it seems as if more pieces of nomenclature are being added every other week. Gradually the experts began explaining that there are kinds and degrees of saturation, and the names of different classifications—sometimes of different individual acids—started showing up in media coverage of health issues. What generally seems to have got lost in the fog of nutribabble is the culinary picture.

Different fats, as we encounter them in the kitchen, contain different balances of saturated and
unsaturated fatty acids. Broadly speaking, the ones more weighted toward unsaturation are liquid at room temperature and are called “oils,” while the more saturated fats are solid at the same temperature. But what’s unique about butter is that because of the huge number of different saturated and unsaturated fatty acids stuck onto triglyceride molecules in different combinations, it undergoes a uniquely subtle
transition between solid and liquid.

You must also take into account that acids of different chain lengths all have their particular
flavors. The shorter ones, which also happen to be somewhat volatile, include the pungent butyric acid and the trio of capric-caproic-caprylic acids that in large amounts produces “goaty-sheepy” effects. The longer ones are usually milder-tasting. Imagine the four hundred–plus chemically distinct fatty acids in cows’-milk butter, all contributing separate jots and
tittles of sharpness, roughness, floweriness, waxiness, mellowness, and meltability to what we taste as a single substance.

The
butter story involves many other wrinkles that can’t be dealt with here; I have ignored whole categories of compounds that enter into its taste and smell. I will mention only one final factor that sets it apart from all other culinary fats: the strategic impurities of “
buttermilk.” If you remember the concept of “
phase inversion” (
this page
), you know that churning milk or cream to butter means agitating an emulsion of fat globules dispersed in a water-based solution, thus breaking up the individual globules enough to let the milkfat inside them separate—more or less—from the rest of the milk and form the continuous mass that we call butter. But butter is never pure butterfat, unless you resort to very drastic industrial separation techniques that produce something lacking the nuances of proper butter. When the formerly dispersed milkfat comes together in a body through churning, it retains minuscule droplets of “buttermilk,” the incompletely separated liquid residue. Even after freshly churned butter is worked and rinsed to remove the buttermilk, faint traces of it remain dispersed through the body of the butter. They contain enough of the original skim-milk solids to contribute a very faint, elusive milkiness without which butter never quite achieves its full flavor potential.

These same milk solids illustrate just how close the rewards of cooking with dairy products are to the pitfalls. They have the wonderful property of browning, caramelizing, and developing a heavenly flavor when butter is heated to fairly low temperatures, somewhere around 250°F. The white stuff that you saw separating from the clear butterfat in slowly heated butter, then resolving itself into nutty browned particles, was milk solids from retained buttermilk. Unfortunately, their burning point is far below the smoking point of the actual butterfat. Let the temperature increase even slightly, and in a flash the delicious brown flecks will become acridly reeking black flecks, the hallmark of irretrievably burned butter.

Most butter as sold in the United States is only about 80 to 81 percent butterfat. The makeup of the remainder varies according to such factors as whether the butter is salted or unsalted and made from sweet or ripened cream. Most of it is water (either in the retained buttermilk or incorporated in the process of rinsing out the buttermilk) and milk solids. For some purposes such as
pastry-making (see the recipe for
Pâte Brisée
), butterfat content of 82 percent or higher is desirable. In most other kinds of cooking, the nuances contributed by trace amounts of buttermilk are actually a virtue—though too much gives the butter a leaky body and a propensity to go bad.

Why does melting butter so irreversibly change its basic consistency? The answer lies in the breaking up of fat globules in the churning process. Milk or cream is ordinarily chilled in preparation for churning. Chilling any liquid fat
to a solid state causes it to form crystals. The enclosure of milkfat within membrane-surrounded globules adds another complication. As some of the globule contents become crystallized, the sharp crystal edges are in effect primed to start rupturing globule membranes even before churning, encouraging the formation of a continuous butter mass. But not entirely continuous; even after churning, some of the original fat globules remain intact, distributed throughout the body of the butter. The cold butter takes on a triple interior structure: part crystalline (which makes it brittle), part continuous (which makes it malleable), part globular. When it melts, this unique architecture is effaced a little at a time along with other changes including the escape of volatile components. Once rechilled, the butter hardens into coarser crystals large enough to be detected as a grainy “mouthfeel.”

The ease with which butter absorbs the
smells and tastes of other foods is yet another effect of membrane disruption. Components that were comparatively impervious to outside influences while they remained locked up in the inner or outer face of the globule membrane are now distributed through the butter. They include various unstable radicals, or unattached fragments of molecules, that are ready to react with whatever they come in contact with. It so happens that raw onions or other alliums, once cut, release their own arsenal of highly reactive volatile sulfurous radicals in search of attachment points on other substances. Put butter in contact with these “allicins” (in fact, nearly anything vigorously smelly), and you have something like the meeting of two desperately lonely people in a singles bar. All fats and oils tend to be affected by foreign aromas and flavors, but the unique composition of butter makes it the most susceptible of all.