Whatever else may be said about them, fats are to be welcomed in cooking.
FATTY FOODS ARE ACCUSED OF BLOCKING our arteries and making us fat. Unsurprisingly, perhaps, one hears calls nowadays for banning fats from the kitchen. Nonetheless, fats are an indispensable part of the cook’s repertoire. Let’s consider the reasons why.
Deep frying, which involves temperatures of 200°C (392°F) or more, gives French fries and fritters their crispiness. Because water cannot withstand such temperatures without boiling, the surface of fried food is dried out without the water inside having time to diffuse outward. The crust that is formed in this way is what produces the sensation of crispiness. If deep-fried foods were cooked in a very hot oven, the results would be different. Chemists in Bristol and Nantes have demonstrated that fats are an essential element of Maillard reactions between sugars and amino acids. These reactions differ depending on the presence or absence of fatty matter; indeed, the good taste of the browned surface of fried foods is directly attributable to fats. It is for this reason that quail, for example, is wrapped in fat or bacon before roasting.
It is a mistake to baste meat with the juices that drip into the roasting pan, by the way; these juices are mostly water, which softens the crispy surface (itself the consequence of the water inside the skin evaporating) and so produces exactly the opposite result of what one hopes to achieve by roasting. Here again fat is the cook’s friend. Ideally one would use a decanting drip pan to recover the melted fat while eliminating the water.
From Roasts to Emulsions
Whether one uses oil or butter, fats are inevitable in mayonnaise, béarnaise, hollandaise, beurre blanc, and other emulsified sauces formed from a base thickened with butter or cream. These emulsions consist almost exclusively of fatty matter. Oil droplets are packed together in water so closely that they no longer have room to move, with the result that the sauce has trouble flowing. In the case of some sauces the coagulation of the egg yolk adds solid particles to the oil droplets dispersed in the water, yielding suspension emulsions rather than emulsions proper.
Might it nonetheless be possible to increase the proportion of water and reduce the proportion of fat? One could use a hand mixer rather than a fork to divide the fatty matter up into smaller and therefore more numerous droplets, but little would be gained. Alternatively, one could use thickeners and gelatinizing agents, but it is difficult to reproduce the fluid behavior of an emulsified sauce in a suspension (of expanded starch granules, for example) or a concentrated solution (as when hydrocolloids—molecules surrounded by a lot of water molecules—are dissolved in water).
This observation may help us finally to transform a small evil into a great good. Butter, for example, acquires an unpleasant odor in the refrigerator because many aromatic molecules are soluble in fats. Makers of perfume exploit this solubility in order to extract fragrances from the most delicate flowers: They place freshly cut blossoms on a neutral fat for a few hours, then discard them and melt the fat in order to recover the aromatic molecules that have dissolved in it. This process is known as enfleurage. Butter serves as the fatty substrate for enfleurage in a refrigerator, as do chocolate (made of cocoa butter) and cream.
Separating Aromas
This property could be put to more systematic use in cooking. Why not wrap cheeses in aromatic plants, for example, so that the aromatic molecules slowly dissolve in the fatty matter of the cheese? We would also do well to recall the underlying principle of a famous recipe for sage butter, recommended in Italy as an accompaniment for pasta: When one cooks the leaves of this herb in butter, the heat causes their cells to burst and release aromatic molecules, which are then dissolved in the melted butter.
Not all aromatic molecules are fat soluble, however. One way to dissolve them is to use a separating funnel, long familiar to chemists as a useful device for separating mixtures. Put oil and water in the funnel, and then add chopped or ground pieces of an aromatic food such as cepe mushrooms. When the funnel is shaken, the hydrophobic aromatic molecules are dissolved in the oil while the hydrophilic aromatic molecules are dissolved in the water.
In this way two flavors are created out of one because the aromatic molecules are different in the two solvents. If you don’t have a separating funnel, simply use a jar that can be hermetically sealed. Put oil and water in it, add an aromatic food, and when the aromatic molecules have been dissolved, slowly drain off the upper oily phase into another container, reserving the watery solution at the bottom.
How can these fragrant solutions be put to good use? If you were to prepare the cepe-scented water using egg whites instead of water, you could incorporate the cepe-scented oil by whisking it into the egg mixture. The egg proteins will then be tensioactive molecules, which will give you a cepe emulsion.