On Food And Cooking Part 74

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Vinaigrette

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Two Liquids: Continuous and Divided The two liquids in an emulsion can be thought of as the container and the contained: one liquid is broken up into separate droplets, and these droplets are contained in and surrounded by the intact ma.s.s of the other liquid. In the usual shorthand, an "oil-in-water" emulsion is one in which oil is dispersed in a continuous water phase; "water-in-oil" names the reverse situation. The dispersed liquid takes the form of tiny droplets, between a ten-thousandth and a tenth of a millimeter across. The droplets are large enough to deflect light rays from their normal path through the surrounding liquid, and give emulsions their characteristically milky appearance. The two liquids in an emulsion can be thought of as the container and the contained: one liquid is broken up into separate droplets, and these droplets are contained in and surrounded by the intact ma.s.s of the other liquid. In the usual shorthand, an "oil-in-water" emulsion is one in which oil is dispersed in a continuous water phase; "water-in-oil" names the reverse situation. The dispersed liquid takes the form of tiny droplets, between a ten-thousandth and a tenth of a millimeter across. The droplets are large enough to deflect light rays from their normal path through the surrounding liquid, and give emulsions their characteristically milky appearance.

The more droplets that are crowded into the continuous phase, the more they get in the water's and each other's way, and the more viscous the emulsion is. In light cream, the fat droplets take up about 20% of the total volume and water 80%; in heavy cream, the droplets are about 40% of the volume; and in stiff, semisolid mayonnaise, oil droplets occupy nearly 80% of the volume. If the cook works more of the dispersed liquid into the emulsion, then it gets thicker; if he adds more of the continuous liquid, then there's more s.p.a.ce between droplets, and the emulsion becomes thinner. Clearly it's important to keep in mind which phase is which.

Because nearly all emulsified sauces are oil-in-water systems, I'll a.s.sume in most of the following discussion that the continuous phase is water, the dispersed phase oil.

Forming Emulsions: Overcoming the Force of Surface Tension It takes work to make an emulsion. We all know from experience that when we pour water and oil into the same bowl, they form two separate layers: one doesn't just turn into tiny droplets and invade the other. The reason for this behavior is that when liquids can't mix for chemical reasons, they spontaneously arrange themselves in a way that minimizes their contact with each other. They form a single large ma.s.s, which exposes less surface area to the other liquid than does the same total ma.s.s broken into pieces. This tendency of liquids to minimize their surface area is an expression of the force called It takes work to make an emulsion. We all know from experience that when we pour water and oil into the same bowl, they form two separate layers: one doesn't just turn into tiny droplets and invade the other. The reason for this behavior is that when liquids can't mix for chemical reasons, they spontaneously arrange themselves in a way that minimizes their contact with each other. They form a single large ma.s.s, which exposes less surface area to the other liquid than does the same total ma.s.s broken into pieces. This tendency of liquids to minimize their surface area is an expression of the force called surface tension. surface tension.

Mayonnaise formation. Two stages in making mayonnaise as seen through a light microscope. One tablespoon/15 ml of oil beaten into 1 egg yolk plus water gives a spa.r.s.e emulsion of coa.r.s.e, unevenly sized oil droplets (left). (left). Eight tablespoons/120 ml of oil give a tightly packed, semisolid emulsion of small droplets Eight tablespoons/120 ml of oil give a tightly packed, semisolid emulsion of small droplets (right). (right). The yolk emulsifiers and stabilizing proteins must be effective enough to withstand considerable physical pressure in order to prevent the oil droplets from coalescing into a separate layer. The yolk emulsifiers and stabilizing proteins must be effective enough to withstand considerable physical pressure in order to prevent the oil droplets from coalescing into a separate layer.

Making Billions of Droplets from One Tablespoon It's on account of surface tension, then, that the cook must pour energy into the liquid to be dispersed. To make a sauce, its natural monolithic arrangement must be shattered. And seriously shattered: when you beat a single tablespoon/15 ml of oil into a mayonnaise, you break it up into about 30 billion separate droplets! Serious whisking by hand or in a kitchen mixer provides enough shearing force to make droplets as small as 3 thousandths of a millimeter across. A blender can get them somewhat smaller, and a powerful industrial h.o.m.ogenizer can reduce them to less than one thousandth of a millimeter. The size of the droplets matters, because smaller droplets are less likely to coalesce with each other and break the sauce into two separate phases again. They also produce a thicker, finer consistency, and seem more flavorful because they have a larger surface area from which aroma molecules can escape and reach our nose. It's on account of surface tension, then, that the cook must pour energy into the liquid to be dispersed. To make a sauce, its natural monolithic arrangement must be shattered. And seriously shattered: when you beat a single tablespoon/15 ml of oil into a mayonnaise, you break it up into about 30 billion separate droplets! Serious whisking by hand or in a kitchen mixer provides enough shearing force to make droplets as small as 3 thousandths of a millimeter across. A blender can get them somewhat smaller, and a powerful industrial h.o.m.ogenizer can reduce them to less than one thousandth of a millimeter. The size of the droplets matters, because smaller droplets are less likely to coalesce with each other and break the sauce into two separate phases again. They also produce a thicker, finer consistency, and seem more flavorful because they have a larger surface area from which aroma molecules can escape and reach our nose.

Two factors make it easier for the cook to generate small droplets. One is the thickness of the continuous phase, which drags harder on the droplets and transfers more shearing force to them from the whisk. Shake a little oil in a bottle of water, and the oil droplets are coa.r.s.e and quickly coalesce; shake a little water in the more viscous oil, and the water gets broken into a persistent cloud of small droplets. It's helpful, then, to start with as viscous a part of the continuous phase as possible, and dilute it with any other ingredients after the emulsion has formed.

The second factor that makes it easier to produce small droplets in an emulsion is the presence of emulsifiers.

Emulsifiers: Lecithin and Proteins Emulsifiers are molecules that lower the surface tension of one liquid dispersed in another, and therefore make it easier to make small droplets and a fine, creamy emulsion. They do so by coating the surface of the droplets, and shielding the droplet surface from the continuous liquid. Emulsifiers are therefore a true liaison: they must be partly soluble in each of the two mutually incompatible liquids. They manage this by having two different regions on the same molecule, one soluble in water and the other in fat. Emulsifiers are molecules that lower the surface tension of one liquid dispersed in another, and therefore make it easier to make small droplets and a fine, creamy emulsion. They do so by coating the surface of the droplets, and shielding the droplet surface from the continuous liquid. Emulsifiers are therefore a true liaison: they must be partly soluble in each of the two mutually incompatible liquids. They manage this by having two different regions on the same molecule, one soluble in water and the other in fat.

There are two general kinds of molecules that can act as emulsifiers. One kind is typified by the egg phosopholipid lecithin. These are relatively small molecules with a fat-like tail that buries itself in the fat phase and an electrically-charged head that is attracted to water molecules (p. 802). The other kind of emulsifier is the proteins, which are much larger molecules, long chains of amino acids that have a number of different fat-compatible and water-compatible regions. The yolk proteins in eggs and the casein proteins in milk and cream are the best protein emulsifiers.

Unstable and stable emulsions. Oil and water are incompatible substances; they can't mix evenly with each other. When oil is whisked into water, the resulting oil droplets tend to coalesce with each other and separate into a layer on top of the water (left). (left). Emulsifiers are molecules with a fat-compatible tail and water-compatible head (p. 802). They embed their long tails in the fat droplets, leaving their electrically-charged heads projecting into the surrounding water. Coated in this way, the droplets repel each other instead of coalescing Emulsifiers are molecules with a fat-compatible tail and water-compatible head (p. 802). They embed their long tails in the fat droplets, leaving their electrically-charged heads projecting into the surrounding water. Coated in this way, the droplets repel each other instead of coalescing (center). (center). Large water-soluble molecules, including starch and proteins, help stabilize emulsions by blocking the fat droplets from each other Large water-soluble molecules, including starch and proteins, help stabilize emulsions by blocking the fat droplets from each other (right). (right).

Stabilizers: Proteins, Starch, Plant Particles Emulsifiers make it easier for the cook to prepare an emulsion, but they don't necessarily result in a stable emulsion. Once formed, the droplets may be so crowded that they b.u.mp into each other or are forced up against each other, and the force of surface tension may pull them together and cause them to coalesce again. Fortunately, there are many kinds of molecules and particles that can help stabilize an emulsion once it's formed. They all have in common the property of getting in the way, so that two approaching droplets encounter the stabilizers rather than each other. Large, bulky molecules like proteins do this well, as do starch, pectins, and gums, and particles of pulverized plant tissue. Ground white mustard seed is especially effective thanks both to its particles and to a gum that it releases when wetted. Tomato paste contains a considerable amount of protein (around 3%) as well as cell particles, and is a useful emulsifier and stabilizer. Emulsifiers make it easier for the cook to prepare an emulsion, but they don't necessarily result in a stable emulsion. Once formed, the droplets may be so crowded that they b.u.mp into each other or are forced up against each other, and the force of surface tension may pull them together and cause them to coalesce again. Fortunately, there are many kinds of molecules and particles that can help stabilize an emulsion once it's formed. They all have in common the property of getting in the way, so that two approaching droplets encounter the stabilizers rather than each other. Large, bulky molecules like proteins do this well, as do starch, pectins, and gums, and particles of pulverized plant tissue. Ground white mustard seed is especially effective thanks both to its particles and to a gum that it releases when wetted. Tomato paste contains a considerable amount of protein (around 3%) as well as cell particles, and is a useful emulsifier and stabilizer.

Bouillabaisse, an Emulsified SoupBouillabaisse is a Provencal fish soup that takes advantage of gelatin's thickening and emulsifying properties. It's made by cooking a variety of whole fish and fish parts, some of them bony and gelatin-producing rather than meaty, in an aromatic broth with some olive oil. The soup is finished at a vigorous boil, which breaks the oil into tiny droplets and coats them with a stabilizing layer of gelatin. The consistency is thus a combination of gelatin's viscosity and the enriching creaminess of the emulsified oil droplets.

Guidelines for Successful Emulsified Sauces Forming Emulsions Emulsions have always been considered fickle concoctions, by chemists as well as cooks. One chemist wrote in 1921 that contemporary books on pharmacy were "filled with elaborate details as to the making of emulsions," and recorded two such details: "If one starts stirring to the right, one must continue stirring to the right, or no emulsion will be formed. Some books go so far as to say that a left-handed man cannot make an emulsion, but that seems a little absurd." The worry is always that at some point the emulsion may break and separate into blobs of oil and water again. This can happen, but it's almost always because the cook has made one of three mistakes: he has added the liquid to be dispersed too quickly to the continuous liquid, or added too much of the dispersed liquid, or allowed the sauce to get either too hot or too cold. Emulsions have always been considered fickle concoctions, by chemists as well as cooks. One chemist wrote in 1921 that contemporary books on pharmacy were "filled with elaborate details as to the making of emulsions," and recorded two such details: "If one starts stirring to the right, one must continue stirring to the right, or no emulsion will be formed. Some books go so far as to say that a left-handed man cannot make an emulsion, but that seems a little absurd." The worry is always that at some point the emulsion may break and separate into blobs of oil and water again. This can happen, but it's almost always because the cook has made one of three mistakes: he has added the liquid to be dispersed too quickly to the continuous liquid, or added too much of the dispersed liquid, or allowed the sauce to get either too hot or too cold.

There are several basic rules that apply to the making of any emulsified sauce: The first materials into the bowl are the continuous phase - usually the water-based ingredient - and at least some emulsifying and stabilizing ingredients. The dispersed phase is always added to the continuous phase, not the other way around: otherwise it can't be dispersed!

The dispersed phase should be added very gradually to begin with, a small spoonful at a time, while the cook whisks or blends the mixture vigorously. Only after an emulsion has formed and developed some viscosity should the oil be added more rapidly.

The proportions of the two phases must be kept in balance. For most emulsified sauces, the volume of the dispersed phase shouldn't exceed three times the volume of the continuous phase. If the droplets are crowded so closely together that they are in continuous contact, then they're more likely to pool together. When the consistency of an emulsion becomes stiff, this is a sign that the cook should add more of the continuous phase to give the droplets more room.

Starting Slowly There's a simple reason for starting the emulsion slowly and carefully, with small amounts of the dispersed phase. In the early mixing, when little or no oil has yet been emulsified, it's easy for large droplets to avoid the churning action of the whisk and collect at the surface. If a large volume of oil is added before the previous one has been fully emulsified, then the bowl may end up with more unemulsified oil than water. The oil then becomes the continuous phase, the normally continuous water becomes dispersed in it, and the result is an inside-out emulsion, oily and runny. By whisking in the first portion of oil in small doses, the cook makes sure to produce and maintain a growing population of small droplets. Then when the rest of the oil is incorporated more rapidly into the already well-emulsified system, the existing droplets work as a kind of mill, automatically breaking down the incoming oil into particles of their own size. In the last stages of sauce making the cook's whisk need not break up the oil drops directly, but has the easier job of mixing the new oil with the sauce, distributing it evenly to all parts of the droplet "mill." There's a simple reason for starting the emulsion slowly and carefully, with small amounts of the dispersed phase. In the early mixing, when little or no oil has yet been emulsified, it's easy for large droplets to avoid the churning action of the whisk and collect at the surface. If a large volume of oil is added before the previous one has been fully emulsified, then the bowl may end up with more unemulsified oil than water. The oil then becomes the continuous phase, the normally continuous water becomes dispersed in it, and the result is an inside-out emulsion, oily and runny. By whisking in the first portion of oil in small doses, the cook makes sure to produce and maintain a growing population of small droplets. Then when the rest of the oil is incorporated more rapidly into the already well-emulsified system, the existing droplets work as a kind of mill, automatically breaking down the incoming oil into particles of their own size. In the last stages of sauce making the cook's whisk need not break up the oil drops directly, but has the easier job of mixing the new oil with the sauce, distributing it evenly to all parts of the droplet "mill."

Using and Storing Emulsified Sauces Once emulsified sauces have been successfully made, there are two basic rules for using them. Once emulsified sauces have been successfully made, there are two basic rules for using them.

The sauce must not get too hot. At high temperatures, the molecules and droplets in a sauce are moving very energetically, and the droplets may collide hard enough to coalesce. Temperatures above 140F/60C also cause the proteins in egg-emulsified sauces to coagulate, so they're no longer able to protect the droplets. And a cooked sauce that is held before serving on gentle heat may lose enough water by evaporation that the dispersed fat droplets become overcrowded. So cooked emulsions should be made and held at warm, rather than hot, temperatures and should not be spooned onto a piece of food still sizzling from the pan.

The sauce must not get too cold. At low temperatures, surface tension increases, making it more likely that neighboring droplets will coalesce. b.u.t.terfat solidifies at room temperature, and some oils do so in the refrigerator. The resulting sharp-edged fat crystals rupture the layer of emulsifier on the droplets, so that they coalesce and separate when stirred or warmed. Refrigerated emulsions often need to be reemulsified before use. (Manufactured mayonnaise is made with oils that remain liquid at refrigerator temperatures.) Rescuing a Separated Sauce When an emulsified sauce breaks and the droplets of the dispersed phase puddle together, there are two ways to reemulsify it. One is simply to throw the sauce in a blender and use its mechanical power to break the dispersed phase apart again. This generally works for sauces that still have plenty of intact emulsifier and stabilizer molecules in the sauce, but not for cooked egg sauces that have been overheated and their proteins coagulated. The second and more reliable technique is to start with a small amount of the continuous phase, perhaps supplemented with an egg yolk and its wealth of emulsifiers and stabilizers, and carefully beat the broken sauce back into it. If proteins in the initial sauce had coagulated from overheating, the lumps should be strained out before reemulsifying; otherwise the rescue process may leave the protein particles too small to strain out, but large enough to leave a grainy impression in the mouth. When an emulsified sauce breaks and the droplets of the dispersed phase puddle together, there are two ways to reemulsify it. One is simply to throw the sauce in a blender and use its mechanical power to break the dispersed phase apart again. This generally works for sauces that still have plenty of intact emulsifier and stabilizer molecules in the sauce, but not for cooked egg sauces that have been overheated and their proteins coagulated. The second and more reliable technique is to start with a small amount of the continuous phase, perhaps supplemented with an egg yolk and its wealth of emulsifiers and stabilizers, and carefully beat the broken sauce back into it. If proteins in the initial sauce had coagulated from overheating, the lumps should be strained out before reemulsifying; otherwise the rescue process may leave the protein particles too small to strain out, but large enough to leave a grainy impression in the mouth.

Cream and b.u.t.ter Sauces Cream and b.u.t.ter don't need to be made into sauces - they themselves are sauces! In fact they're prototypes for sauces in general, with their lingering, mouthfilling consistency and rich but delicate flavor. A ramekin of melted b.u.t.ter in which to dip a morsel of lobster or an artichoke leaf, a pour of cream over fresh berries or pastry - these are wonderful combinations. But cream and b.u.t.ter are versatile ingredients, and cooks have found other ways to exploit them in saucemaking.

Milk and Cream Emulsions Cream owes its versatility to its origins in milk. Milk is a complex dispersion whose continuous phase is water, and whose dispersed phases are milkfat in the form of microscopic droplets, or globules, and protein particles in the form of casein aggregates (p. 19). The droplets are coated with a thin membrane of emulsifiers, both lecithin-like phospholipids and certain proteins; and other noncasein proteins float free in the water. Both the globule membranes and the various proteins are tolerant of heat: so plain milk and cream can be boiled hard without the fat globules coalescing and separating, or the proteins coagulating and curdling. Cream owes its versatility to its origins in milk. Milk is a complex dispersion whose continuous phase is water, and whose dispersed phases are milkfat in the form of microscopic droplets, or globules, and protein particles in the form of casein aggregates (p. 19). The droplets are coated with a thin membrane of emulsifiers, both lecithin-like phospholipids and certain proteins; and other noncasein proteins float free in the water. Both the globule membranes and the various proteins are tolerant of heat: so plain milk and cream can be boiled hard without the fat globules coalescing and separating, or the proteins coagulating and curdling.

Whole milk is only about 4% fat, so its fat globules are too few and far between to block the flow of the water phase and give much of an impression of thickness. Cream is a portion of milk in which the fat globules have been concentrated and crowded: light cream is around 18% fat, and heavy or whipping cream around 38%. In addition to its fat supply, cream offers proteins and emulsifying molecules that can help stabilize other, more fragile emulsions (beurre blanc).

Heavy Cream Resists Curdling The casein proteins in milk and cream are stable to boiling temperatures, but they're sensitive to acidity, and the combination of heat and acid will cause them to curdle. Many sauces include flavorful acid ingredients: saute pans are often deglazed with wine, for example. This means that most milk and cream products, including light cream and sour cream, can't actually be cooked to make a sauce; they must be added as a last-minute enrichment. The exceptions are heavy cream and creme fraiche, which contain so little casein that its curdling simply isn't noticeable (p. 29). The casein proteins in milk and cream are stable to boiling temperatures, but they're sensitive to acidity, and the combination of heat and acid will cause them to curdle. Many sauces include flavorful acid ingredients: saute pans are often deglazed with wine, for example. This means that most milk and cream products, including light cream and sour cream, can't actually be cooked to make a sauce; they must be added as a last-minute enrichment. The exceptions are heavy cream and creme fraiche, which contain so little casein that its curdling simply isn't noticeable (p. 29).

Reduced Cream When heavy cream is added to another liquid to enrich and thicken it - to a meat sauce, or deglazing liquid, or a vegetable puree - then of course its fat globules are diluted and its consistency thins down. In order to make cream a more effective thickener, cooks concentrate it even further by boiling off water from the continuous phase. When the volume of cream is reduced by a third, the globule concentration reaches 55% and the consistency is like that of a light starchthickened sauce; when reduced by half, the globules take up 75% of the volume and the consistency is very thick, almost semisolid. Stirred into a thinner liquid, these reduced creams have enough fat globules to fill it and lend a substantial body. Cream reduction and thickening can also be done at the last minute, for example after a saute pan has been deglazed; the cook adds cream to the deglazing liquid and boils the mixture until it reaches the desired consistency. When heavy cream is added to another liquid to enrich and thicken it - to a meat sauce, or deglazing liquid, or a vegetable puree - then of course its fat globules are diluted and its consistency thins down. In order to make cream a more effective thickener, cooks concentrate it even further by boiling off water from the continuous phase. When the volume of cream is reduced by a third, the globule concentration reaches 55% and the consistency is like that of a light starchthickened sauce; when reduced by half, the globules take up 75% of the volume and the consistency is very thick, almost semisolid. Stirred into a thinner liquid, these reduced creams have enough fat globules to fill it and lend a substantial body. Cream reduction and thickening can also be done at the last minute, for example after a saute pan has been deglazed; the cook adds cream to the deglazing liquid and boils the mixture until it reaches the desired consistency.

Creme Fraiche in Sauce Making Reduced creams have several disadvantages. They take time and attention to prepare, develop a cooked flavor, and are very rich, sometimes overly so for the balance of a given sauce. A useful alternative to reduced creams is creme fraiche, a version of heavy cream whose consistency has been thickened not by boiling down, but by fermentation (p. 49). The acid produced by lactic bacteria causes the casein proteins in the water phase to cl.u.s.ter together and form a network that immobilizes the water. Some strains of bacteria also secrete long carbohydrate molecules that further thicken the water phase and act as stabilizers. Used in place of reduced cream, creme fraiche requires no preparation, is less rich, and has a fresher flavor. Thanks to its low protein content, it tolerates temperatures that would curdle sour cream. Reduced creams have several disadvantages. They take time and attention to prepare, develop a cooked flavor, and are very rich, sometimes overly so for the balance of a given sauce. A useful alternative to reduced creams is creme fraiche, a version of heavy cream whose consistency has been thickened not by boiling down, but by fermentation (p. 49). The acid produced by lactic bacteria causes the casein proteins in the water phase to cl.u.s.ter together and form a network that immobilizes the water. Some strains of bacteria also secrete long carbohydrate molecules that further thicken the water phase and act as stabilizers. Used in place of reduced cream, creme fraiche requires no preparation, is less rich, and has a fresher flavor. Thanks to its low protein content, it tolerates temperatures that would curdle sour cream.

b.u.t.ter Like its parent material, cream, b.u.t.ter is an emulsion: but it's one of the few food emulsions in which the continuous phase is fat, not water. In fact, b.u.t.ter is made by "inverting" the fat-in-water cream emulsion to produce a water-in-fat emulsion (p. 33). The continuous fat phase of b.u.t.ter, together with some intact fat globules that survived churning, takes up about 80% of its volume, and the dispersed water droplets about 15%. When it melts, the heavier water droplets sink to the bottom and form a separate layer. The consistency of melted b.u.t.ter, then, is the consistency of the b.u.t.terfat itself, which thanks to its long fat molecules is naturally more slow-flowing and viscous than water. So melted b.u.t.ter, whole or clarified ("drawn") to remove the water phase, makes a simple and delicious sauce. Cooks also heat whole b.u.t.ter until the water boils off and the milk solids turn brown, which gives the fat a nutty aroma. The French Like its parent material, cream, b.u.t.ter is an emulsion: but it's one of the few food emulsions in which the continuous phase is fat, not water. In fact, b.u.t.ter is made by "inverting" the fat-in-water cream emulsion to produce a water-in-fat emulsion (p. 33). The continuous fat phase of b.u.t.ter, together with some intact fat globules that survived churning, takes up about 80% of its volume, and the dispersed water droplets about 15%. When it melts, the heavier water droplets sink to the bottom and form a separate layer. The consistency of melted b.u.t.ter, then, is the consistency of the b.u.t.terfat itself, which thanks to its long fat molecules is naturally more slow-flowing and viscous than water. So melted b.u.t.ter, whole or clarified ("drawn") to remove the water phase, makes a simple and delicious sauce. Cooks also heat whole b.u.t.ter until the water boils off and the milk solids turn brown, which gives the fat a nutty aroma. The French beurre noisette beurre noisette and and beurre noir, beurre noir, or "hazelnut" and "black" b.u.t.ters, are such browned b.u.t.ters, often made into a temporary emulsion with lemon juice and vinegar respectively. or "hazelnut" and "black" b.u.t.ters, are such browned b.u.t.ters, often made into a temporary emulsion with lemon juice and vinegar respectively.

Compound and Whipped b.u.t.ters There are other ways to take advantage of b.u.t.ter's semisolid consistency and background richness. One is to make a "compound b.u.t.ter" by incorporating pounded herbs, spices, sh.e.l.lfish eggs or livers, or other ingredients; another is to whip softened b.u.t.ter with a flavorful liquid into a combined emulsion and foam. Pieces or dollops of these flavored b.u.t.ters can then be melted into a rich, flavorful coating atop a piece of meat or fish, or on some vegetables or pasta, or they can be swirled into an otherwise finished sauce. There are other ways to take advantage of b.u.t.ter's semisolid consistency and background richness. One is to make a "compound b.u.t.ter" by incorporating pounded herbs, spices, sh.e.l.lfish eggs or livers, or other ingredients; another is to whip softened b.u.t.ter with a flavorful liquid into a combined emulsion and foam. Pieces or dollops of these flavored b.u.t.ters can then be melted into a rich, flavorful coating atop a piece of meat or fish, or on some vegetables or pasta, or they can be swirled into an otherwise finished sauce.

Turning b.u.t.ter Back into Cream: Enriching Sauces with b.u.t.ter b.u.t.ter is remarkable for being a convertible emulsion. This offspring of cream can be turned back into cream! Its convertibility is what makes b.u.t.ter so useful as a finishing enrichment for many sauces, including simple pan deglazings, and it's what makes possible the sauce called beurre blanc, literally "white b.u.t.ter." There's only one requirement for converting b.u.t.ter into the equivalent of cream with 80% fat: the process must start in a small amount of water. If you melt b.u.t.ter on its own, the fat phase remains the continuous phase, and the water droplets settle out of it. But if you melt b.u.t.ter in some water, then you're starting with water as the continuous phase. As the fat molecules are released into the water, they're surrounded by water - and by the substances contained in the b.u.t.ter's own water droplets, which merge right into the cooking water. The droplets contain milk proteins and remnants of the emulsifier membranes that coated the fat globules in the original cream. And those protein and phospholipid remnants rea.s.semble themselves onto the fat as it melts into the water, coating and protecting separate fat droplets and forming the fat-in-water emulsion. However, the droplet coatings in this reconst.i.tuted cream are spa.r.s.er and more fragile than the original fat-globule membranes, and will begin to leak fat if heated close to 140F/60C. b.u.t.ter is remarkable for being a convertible emulsion. This offspring of cream can be turned back into cream! Its convertibility is what makes b.u.t.ter so useful as a finishing enrichment for many sauces, including simple pan deglazings, and it's what makes possible the sauce called beurre blanc, literally "white b.u.t.ter." There's only one requirement for converting b.u.t.ter into the equivalent of cream with 80% fat: the process must start in a small amount of water. If you melt b.u.t.ter on its own, the fat phase remains the continuous phase, and the water droplets settle out of it. But if you melt b.u.t.ter in some water, then you're starting with water as the continuous phase. As the fat molecules are released into the water, they're surrounded by water - and by the substances contained in the b.u.t.ter's own water droplets, which merge right into the cooking water. The droplets contain milk proteins and remnants of the emulsifier membranes that coated the fat globules in the original cream. And those protein and phospholipid remnants rea.s.semble themselves onto the fat as it melts into the water, coating and protecting separate fat droplets and forming the fat-in-water emulsion. However, the droplet coatings in this reconst.i.tuted cream are spa.r.s.er and more fragile than the original fat-globule membranes, and will begin to leak fat if heated close to 140F/60C.

Any water-based sauce can thus be thickened and enriched simply by swirling a pat of b.u.t.ter into it at the end. This is especially handy in the last-minute thickening of pan juices, which don't have the benefit of containing much gelatin or any starch. Incorporating one volume of b.u.t.ter into three volumes of deglazing liquid - off the heat, to avoid damaging the fragile droplet coatings - will produce a consistency (and fat content) approximating that of light cream.

In purees and starch-thickened sauces, a small amount of b.u.t.ter (or cream) lubricates the solid thickeners and lends a smoother consistency. Because these sauces are rich in emulsion-stabilizing molecules and particles, they can be heated to the boil without causing the reconst.i.tuted fat droplets to separate.

Beurre Blanc The French sauce The French sauce beurre blanc beurre blanc probably evolved from the practice of enriching cooking liquids with b.u.t.ter. It's made by preparing a flavorful reduction of vinegar and/or wine, then whisking pieces of b.u.t.ter into the reduction. Each piece of b.u.t.ter carries all the ingredients necessary for a new portion of sauce, so the cook can whisk in one piece of b.u.t.ter, or 100. The proportions are entirely up to the cook's taste and needs. The consistency of beurre blanc is like that of thick cream, and can be made somewhat thicker by adding water-free clarified b.u.t.ter once the initial emulsion has been formed. The phospholipids and proteins carried in the b.u.t.ter's water are capable of emulsifying two to three times the b.u.t.terfat in which they're embedded. probably evolved from the practice of enriching cooking liquids with b.u.t.ter. It's made by preparing a flavorful reduction of vinegar and/or wine, then whisking pieces of b.u.t.ter into the reduction. Each piece of b.u.t.ter carries all the ingredients necessary for a new portion of sauce, so the cook can whisk in one piece of b.u.t.ter, or 100. The proportions are entirely up to the cook's taste and needs. The consistency of beurre blanc is like that of thick cream, and can be made somewhat thicker by adding water-free clarified b.u.t.ter once the initial emulsion has been formed. The phospholipids and proteins carried in the b.u.t.ter's water are capable of emulsifying two to three times the b.u.t.terfat in which they're embedded.

Beurre blanc will begin to separate and leak b.u.t.terfat if its temperature rises above about 135F/58C. However, the phospholipid emulsifiers can tolerate heat and re-form a protective layer. An overheated sauce can usually be restored with a small amount of cool water and brisk whisking. The addition of a spoonful of cream supplies more emulsifying materials and can make a beurre blanc more stable. Most damaging to beurre blanc is letting it cool below body temperature. The b.u.t.terfat solidifies and forms crystals around 85F/30C, and the crystals poke through the thin membrane of emulsifiers and fuse with each other, forming a continuous network of fat that separates when the sauce is reheated. Ideally, beurre blanc should be kept at around 125F/52C. Because water will evaporate at this temperature and may overconcentrate the fat phase, it's a good idea to add a little water periodically if the sauce has to be held for any time.

Beurre Monte A preparation closely related to beurre blanc is A preparation closely related to beurre blanc is beurre monte, beurre monte, "worked up" or "prepared" b.u.t.ter, which is simply an unflavored beurre blanc made with an initial dose of water rather than vinegar or wine. Beurre monte is used among other things as a poaching medium. Thanks to the relatively low heat conductivity and heat capacity of fat compared to water, it cooks delicate fish and meats more gradually than does a broth at the same temperature. "worked up" or "prepared" b.u.t.ter, which is simply an unflavored beurre blanc made with an initial dose of water rather than vinegar or wine. Beurre monte is used among other things as a poaching medium. Thanks to the relatively low heat conductivity and heat capacity of fat compared to water, it cooks delicate fish and meats more gradually than does a broth at the same temperature.

Eggs as Emulsifiers As we've already seen, cooks can use egg yolks to thicken all kinds of hot sauces. The yolk proteins unfold and bond to each other when heated, and so form a liquid-immobilizing network (p. 604). Egg yolks are also very effective emulsifiers, and for asimple reason: they themselves are a concentrated and complex emulsion of fat in water, and are therefore filled with emulsifying molecules and molecule aggregates.

Emulsifying Particles and Proteins Of the various yolk components, two in particular provide most of the emulsifying power. One is the low-density lipoproteins or LDLs (the same LDLs that circulate in our blood and whose levels are measured in blood tests because they carry potentially artery-blocking cholesterol). LDLs are particles made up of emulsifying proteins, phospholipids, and cholesterol, all surrounding a core of fat molecules. The intact LDL particles appear to be more effective emulsifiers than any of their components. The other major emulsifying particles are the larger yolk granules, which contain both LDLs and HDLs (the "good-cholesterol" high-density lipoproteins are even more effective emulsifiers than LDL) as well as dispersed emulsifying protein, phosvitin. Yolk granules are so large that they can't cover a droplet surface very well, but when they're exposed to moderate concentrations of salt they fall apart into their separate LDLs, HDLs, and proteins, and these are very effective indeed. Of the various yolk components, two in particular provide most of the emulsifying power. One is the low-density lipoproteins or LDLs (the same LDLs that circulate in our blood and whose levels are measured in blood tests because they carry potentially artery-blocking cholesterol). LDLs are particles made up of emulsifying proteins, phospholipids, and cholesterol, all surrounding a core of fat molecules. The intact LDL particles appear to be more effective emulsifiers than any of their components. The other major emulsifying particles are the larger yolk granules, which contain both LDLs and HDLs (the "good-cholesterol" high-density lipoproteins are even more effective emulsifiers than LDL) as well as dispersed emulsifying protein, phosvitin. Yolk granules are so large that they can't cover a droplet surface very well, but when they're exposed to moderate concentrations of salt they fall apart into their separate LDLs, HDLs, and proteins, and these are very effective indeed.

Using Eggs to Emulsify Sauces As emulsifiers, egg yolks are most effective when they're raw, and when they're warm. Fresh out of the refrigerator, the various yolk particles move only sluggishly and don't coat the fat droplets as quickly and completely. When yolks are cooked, the proteins unfold and coagulate, thus ending their usefulness as flexible surface coatings. Hard-cooked yolks are sometimes used instead of raw yolks to make emulsified sauces; their disadvantage is that the proteins have been coagulated in place and phospholipids probably trapped in the coagulated particles, so they have far less emulsifying power, and the yolk texture can give a subtle graininess. As emulsifiers, egg yolks are most effective when they're raw, and when they're warm. Fresh out of the refrigerator, the various yolk particles move only sluggishly and don't coat the fat droplets as quickly and completely. When yolks are cooked, the proteins unfold and coagulate, thus ending their usefulness as flexible surface coatings. Hard-cooked yolks are sometimes used instead of raw yolks to make emulsified sauces; their disadvantage is that the proteins have been coagulated in place and phospholipids probably trapped in the coagulated particles, so they have far less emulsifying power, and the yolk texture can give a subtle graininess.

And egg whites? They're a less concentrated source of protein, and designed for a fat-free, watery environment, and therefore of little help in coating fat droplets. However, the white proteins provide some viscosity thanks to their large size and loose a.s.sociations with each other, so they have some value as emulsion stabilizers.

Oil droplets in mayonnaise. A view through an electron microscope. Protein and emulsifier molecules and aggregates, all from egg yolk, are present between the large droplets and on their surfaces, and help prevent them from coalescing.

Cold Egg Sauces: Mayonnaise Mayonnaise is an emulsion of oil droplets suspended in a base composed of egg yolk, lemon juice or vinegar, water, and often mustard, which provides both flavor and stabilizing particles and carbohydrates (p. 417). It's the sauce most tightly packed with oil droplets - as much as 80% of its volume is oil - and is usually dense and too stiff to pour. It can be thinned and flavored with various water-based liquids, including purees and stocks, or it can enrich such liquids the way cream does; it can also be aerated with the addition of whipped cream or egg whites. As a room-temperature preparation, mayonnaise is generally served with cold dishes of various sorts. But thanks to the yolk proteins, it also reacts usefully to heat. It lends body and richness when added to thin broths and briefly cooked; and when layered onto fish or vegetables and broiled, it moderates the heat, puffs up and sets into a rich coating.

Traditionally, mayonnaise is made with raw egg yolks, and therefore carries a slight risk of salmonella infection. Manufacturers use pasteurized yolks, and cooks concerned about salmonella can now find pasteurized eggs in supermarkets. Both vinegar and extra-virgin olive oil kill bacteria, but mayonnaise is best treated as a highly perishable food that should be served immediately or kept refrigerated.

Making Mayonnaise All of the ingredients for making mayonnaise should be at room temperature; warmth speeds the transfer of emulsifiers from the yolk particles to the oil droplet surfaces. The simplest method is to mix together everything but the oil - egg yolks, lemon juice or vinegar, salt, mustard - and then whisk in the oil, slowly at first and more rapidly as the emulsion thickens. However, the cook can produce more stable small droplets by whisking a portion of the oil into just the yolks and salt to start, and then adding the remaining ingredients when the emulsion gets stiff and needs to be thinned. The salt causes the yolk granules to fall apart into its component particles, which makes the yolks become both more clear and more viscous. If left undiluted, this viscosity will help break the oil into smaller droplets. All of the ingredients for making mayonnaise should be at room temperature; warmth speeds the transfer of emulsifiers from the yolk particles to the oil droplet surfaces. The simplest method is to mix together everything but the oil - egg yolks, lemon juice or vinegar, salt, mustard - and then whisk in the oil, slowly at first and more rapidly as the emulsion thickens. However, the cook can produce more stable small droplets by whisking a portion of the oil into just the yolks and salt to start, and then adding the remaining ingredients when the emulsion gets stiff and needs to be thinned. The salt causes the yolk granules to fall apart into its component particles, which makes the yolks become both more clear and more viscous. If left undiluted, this viscosity will help break the oil into smaller droplets.

Though cookbooks often say that the ratio of oil to egg yolk is critical, that one yolk can only emulsify a half-cup or cup of oil, this just isn't true. A single yolk can emulsify a dozen cups of oil or more. What is is critical is the ratio of oil to water: there must be enough of the continuous phase for the growing population of oil droplets to fit into. For every volume of oil added, the cook should provide about a third of that volume in the combination of yolks, lemon juice, vinegar, water, or some other water-based liquid. critical is the ratio of oil to water: there must be enough of the continuous phase for the growing population of oil droplets to fit into. For every volume of oil added, the cook should provide about a third of that volume in the combination of yolks, lemon juice, vinegar, water, or some other water-based liquid.

A Sensitive Sauce Because mayonnaise is chock-full of oil, so much so that the droplets press up against each other, its emulsion is easily damaged by extremes of cold, heat, and agitation. It will tend to leak oil in near-freezing refrigerators and on hot rather than warm food. These problems are ameliorated in manufactured mayonnaise by the addition of stabilizers, usually long carbohydrate or protein molecules that fill the s.p.a.ces between droplets. American bottled "salad dressing" is a very stable hybrid of mayonnaise and a boiled white sauce made with water instead of milk. The texture of such modified sauces, however, is noticeably different from the dense, creamy original. Refrigerated mayonnaise should be handled gently, since some oil may have crystallized and escaped from their droplets. If so, stir gently to reemulsify it, perhaps with the addition of a few drops of water. Because mayonnaise is chock-full of oil, so much so that the droplets press up against each other, its emulsion is easily damaged by extremes of cold, heat, and agitation. It will tend to leak oil in near-freezing refrigerators and on hot rather than warm food. These problems are ameliorated in manufactured mayonnaise by the addition of stabilizers, usually long carbohydrate or protein molecules that fill the s.p.a.ces between droplets. American bottled "salad dressing" is a very stable hybrid of mayonnaise and a boiled white sauce made with water instead of milk. The texture of such modified sauces, however, is noticeably different from the dense, creamy original. Refrigerated mayonnaise should be handled gently, since some oil may have crystallized and escaped from their droplets. If so, stir gently to reemulsify it, perhaps with the addition of a few drops of water.

Making mayonnaise. The cook begins with a small volume of the water phase - mostly egg yolk - and slowly beats oil into droplets in this base (left). (left). As more oil is incorporated, the mixture becomes thicker and the oil is broken into smaller droplets As more oil is incorporated, the mixture becomes thicker and the oil is broken into smaller droplets (center). (center). When the sauce is done, as much as 80% of its volume is occupied by oil droplets, and its consistency is semisolid When the sauce is done, as much as 80% of its volume is occupied by oil droplets, and its consistency is semisolid (right). (right).

Hot Egg Sauces: Hollandaise and Bearnaise The cla.s.sic hot egg sauces, hollandaise and bearnaise and their offspring, are egg-emulsified b.u.t.ter sauces. They are similar to mayonnaise in many respects, but of course must be hot to keep the b.u.t.ter fluid. Their dispersed fat phase is usually a smaller proportion of the sauce, between one-and two-thirds of the total volume. Hollandaise and bearnaise differ mainly in seasoning; hollandaise is only lightly flavored with lemon juice, while bearnaise begins with a tart and aromatic reduction of wine, vinegar, tarragon, and shallots.

Heat Thickens - and Curdles The consistency of the hot egg sauces depends on two factors. One is the form and amount in which the b.u.t.ter is incorporated. Whole b.u.t.ter is about 15% water, so each addition thins the egg phase and the sauce as a whole; clarified b.u.t.ter is all b.u.t.terfat, and thickens the sauce with every addition. The second influence on consistency is the degree to which the egg yolks are heated and thickened. The main trick in making these sauces is to heat the egg yolks enough to obtain the desired thickness, but not so much that the yolk proteins coagulate into little solid curds and the sauce separates. This happens at around 160170F/7077C. A double boiler or a saucepan resting above a larger pan of simmering water will guarantee a gentle and even heat but will also slow the cooking; for this reason, some cooks prefer the riskier but rapid direct heat of a burner. Heating the yolks with the acidic reduction also minimizes curdling; if the pH is around 4.5, the equivalent of yogurt's acidity, the yolks can be safely heated to 195F/90C. (The acid causes the proteins to repel each other, so that they unfold before bonding to each other and form an extended network rather than dense curds.) Cooks concerned about salmonella should make sure the yolks are cooked at least to 160F/70C, or else should use pasteurized eggs. The consistency of the hot egg sauces depends on two factors. One is the form and amount in which the b.u.t.ter is incorporated. Whole b.u.t.ter is about 15% water, so each addition thins the egg phase and the sauce as a whole; clarified b.u.t.ter is all b.u.t.terfat, and thickens the sauce with every addition. The second influence on consistency is the degree to which the egg yolks are heated and thickened. The main trick in making these sauces is to heat the egg yolks enough to obtain the desired thickness, but not so much that the yolk proteins coagulate into little solid curds and the sauce separates. This happens at around 160170F/7077C. A double boiler or a saucepan resting above a larger pan of simmering water will guarantee a gentle and even heat but will also slow the cooking; for this reason, some cooks prefer the riskier but rapid direct heat of a burner. Heating the yolks with the acidic reduction also minimizes curdling; if the pH is around 4.5, the equivalent of yogurt's acidity, the yolks can be safely heated to 195F/90C. (The acid causes the proteins to repel each other, so that they unfold before bonding to each other and form an extended network rather than dense curds.) Cooks concerned about salmonella should make sure the yolks are cooked at least to 160F/70C, or else should use pasteurized eggs.

Olive Oil Can Make Crazy MayonnaiseMayonnaise can be made with any kind of oil. One popular choice, unrefined extra virgin olive oil, often produces an unstable mayonnaise, one that forms properly, but then separates just an hour or two later. Ironically, the likely troublemakers are molecules with emulsifying abilities: oil molecules that have been broken into fragments that have a fat-like tail and water-soluble head, just like lecithin (p. 802). They are concentrated in the oil, and when the cook breaks the oil into droplets, they move to the droplet surface, where they end up pushing the bulkier, more effective egg emulsifiers off the droplet surfaces. Because the droplets are crowded tightly together, this causes the droplets to coalesce and form puddles of oil.This delayed disintegration of olive-oil mayonnaise is well known in Italy, where the sauce is said to "go crazy" (impazzire). Old and improperly stored oils are most likely to have suffered damage to their oil molecules and therefore to cause problems in mayonnaise. Two ways to avoid crazy mayonnaise are to use refined olive oil, and to use extra-virgin oil as a flavoring, with the bulk of the oil being any flavorless refined oil.

Making Hollandaise and Bearnaise There are at least five different ways of making hollandaise and bearnaise, each with its advantages and disadvantages. There are at least five different ways of making hollandaise and bearnaise, each with its advantages and disadvantages.

Cook the egg and water-based ingredients first to a thick consistency, then whisk in pats of whole b.u.t.ter to emulsify the b.u.t.terfat and thin the continuous phase. This is Careme's method, and is the trickiest because the small volume of the initial egg mixture is easily overcooked.

Warm the yolks and water-based ingredients, whisk in either whole or clarified b.u.t.ter, then cook the mixture until it reaches the desired consistency. This is Escoffier's method, and has the advantage that the cook can control the final consistency directly, and by heating the entire volume of sauce.

Put all of the ingredients for the sauce in a cold saucepan, turn the heat on low, and start stirring. The b.u.t.ter gradually melts and releases itself into the egg phase as both heat up together, and the cook then continues to heat the formed sauce until it reaches the desired consistency. This is the simplest method.

Don't cook the yolks at all; just warm them and the water-based ingredients above the melting point of b.u.t.ter, then whisk clarified b.u.t.ter in until the crowding of droplets creates the desired consistency. This is essentially a b.u.t.ter mayonnaise, and eliminates the possibility of overcooking the yolks.

Make the b.u.t.ter-sauce version of a sabayon (p. 639). Whisk the egg yolks and some water while heating them until they form an airy foam, and then gently incorporate melted or clarified b.u.t.ter and the lemon juice or acid reduction. This version is of course much lighter, and is also made with less b.u.t.ter per yolk.

It's possible to make hot egg sauces with fats and oils other than b.u.t.ter, and to flavor the water phase with meat reductions or vegetable purees.

Alternative Oil EmulsionsThese days we think of mayonnaise exclusively as an egg-emulsified sauce, but this hasn't always been the case, and there are a number of other ways to form and stabilize a flavorful oil emulsion. In 1828, perhaps a few decades after the supposed invention of mayonnaise, the great chef and sauce-systematizer Antonin Careme gave three recipes for magnonnaise blanche, magnonnaise blanche, only one of which includes egg yolks. The others are made with a ladleful of starchy veloute or bechamel sauce, and with a gelatinous reduced extract of veal meat and bones. In these versions, gelatin and milk proteins (in the bechamel) are emulsifiers, and starch is a stabilizer. Some versions of the herb-flavored Italian only one of which includes egg yolks. The others are made with a ladleful of starchy veloute or bechamel sauce, and with a gelatinous reduced extract of veal meat and bones. In these versions, gelatin and milk proteins (in the bechamel) are emulsifiers, and starch is a stabilizer. Some versions of the herb-flavored Italian salsa verde, salsa verde, "green sauce," emulsify olive oil with a hard-boiled yolk and bread. The Provencal "green sauce," emulsify olive oil with a hard-boiled yolk and bread. The Provencal aioli aioli and Greek and Greek skorthalia skorthalia are emulsified with a combination of pounded garlic and cooked potato; garlic and bread are also used, as are fresh cheeses. None of these ingredients is as effective at emulsifying and stabilizing as a raw egg yolk, so they will emulsify less oil and the sauces will tend to leak some free oil. are emulsified with a combination of pounded garlic and cooked potato; garlic and bread are also used, as are fresh cheeses. None of these ingredients is as effective at emulsifying and stabilizing as a raw egg yolk, so they will emulsify less oil and the sauces will tend to leak some free oil.

Holding and Salvaging Hot Egg Sauces b.u.t.ter sauces need to be kept warm to prevent the b.u.t.ter from solidifying, and are best held at around 145F/63C to discourage the growth of bacteria. Because the egg proteins slowly continue to bond to each other at this temperature, the cook should stir the sauce occasionally to keep it from thickening. The container should be covered to prevent the sauce's moisture from evaporating and overcrowding the fat droplets, and to prevent the formation of a protein skin on the surface. b.u.t.ter sauces need to be kept warm to prevent the b.u.t.ter from solidifying, and are best held at around 145F/63C to discourage the growth of bacteria. Because the egg proteins slowly continue to bond to each other at this temperature, the cook should stir the sauce occasionally to keep it from thickening. The container should be covered to prevent the sauce's moisture from evaporating and overcrowding the fat droplets, and to prevent the formation of a protein skin on the surface.

Curdled egg sauces can be rescued by straining out the solid bits of protein, keeping the whole mess warm, beginning with another warm egg yolk and one tablespoon/15 ml water, and slowly whisking the sauce into the new yolk. The same technique will revive a sauce that has been refrigerated and so had its b.u.t.terfat crystallized; the crystals melt to form fat puddles when the sauce is simply rewarmed.

Vinaigrettes A Water-in-Oil Emulsion The most commonly and easily made emulsified sauce is the simple oil-and-vinegar salad dressing known as The most commonly and easily made emulsified sauce is the simple oil-and-vinegar salad dressing known as vinaigrette, vinaigrette, from the French word for "vinegar." Vinaigrette does a good job of clinging to lettuce leaves and other vegetables, and lending a refreshing tart counterpoint to their taste. The standard proportions for a vinaigrette are 3 parts oil to 1 vinegar, similar to the proportions in mayonnaise, but the preparation is much simpler. The liquids and other flavorings - salt, pepper, herbs - are often simply shaken into a cloudy, temporary emulsion at the last minute, then poured onto and mixed with the salad. When made in this casual way, a vinaigrette is the odd sauce out: instead of being oil droplets dispersed in water, it's water (vinegar) droplets dispersed in oil. Without the help of an emulsifier, one part of water simply cannot accommodate three parts of oil, so the more voluminous phase, the oil, becomes the continuous phase. from the French word for "vinegar." Vinaigrette does a good job of clinging to lettuce leaves and other vegetables, and lending a refreshing tart counterpoint to their taste. The standard proportions for a vinaigrette are 3 parts oil to 1 vinegar, similar to the proportions in mayonnaise, but the preparation is much simpler. The liquids and other flavorings - salt, pepper, herbs - are often simply shaken into a cloudy, temporary emulsion at the last minute, then poured onto and mixed with the salad. When made in this casual way, a vinaigrette is the odd sauce out: instead of being oil droplets dispersed in water, it's water (vinegar) droplets dispersed in oil. Without the help of an emulsifier, one part of water simply cannot accommodate three parts of oil, so the more voluminous phase, the oil, becomes the continuous phase.

There are good reasons for making oil the continuous phase of a vinaigrette, and for not worrying about the stability of the emulsion. Where many sauces are served under or atop large pieces of food, oil-and-vinegar emulsions are used almost exclusively as salad dressings, whose role is to provide a very fine and even coat for the extensive surface area of lettuce leaves and cut vegetables. A thin, mobile sauce is more effective at this than a thick, creamy one, and oil adheres to the vegetable surfaces better than the water-based vinegar, whose high surface tension causes it to bead up rather than leave a film. And because the sauce is so spread out, it doesn't matter as much that the dispersed droplets be carefully stabilized. Because water and oil are antagonists, the salad fixings should be well dried before they're tossed with vinaigrette; surfaces wet with water will repel the oil.

Making a vinaigrette dressing. The proportion of oil to the water phase in a vinaigrette is similar to the proportion in mayonnaise, but in a vinaigrette the water is the phase dispersed in droplets, and the oil is the continuous phase. This emulsion is much less crowded with droplets, and accordingly a vinaigrette is more fluid than mayonnaise.

Untraditional Vinaigrettes Nowadays the term Nowadays the term vinaigrette vinaigrette is used very broadly to mean almost any kind of emulsified sauce enlivened with vinegar, whether water-in-oil or oil-in-water, cold or hot, destined for salads or vegetables or meats or fish. You can make an oil-in-water version simply by changing the proportions: reducing the oil content and diluting the vinegar with other watery ingredients to provide more of the continuous phase without excessive acidity. Creamy but thin oil-in-water vinaigrettes can spread and cling reasonably well, and have the advantage over a cla.s.sic vinaigrette of being slower to discolor and wilt lettuce leaves. (Oil seeps through breaks in the waxy leaf cuticle and spreads into the leaf interior, where it displaces air and causes the leaf to darken and its structure to collapse.) is used very broadly to mean almost any kind of emulsified sauce enlivened with vinegar, whether water-in-oil or oil-in-water, cold or hot, destined for salads or vegetables or meats or fish. You can make an oil-in-water version simply by changing the proportions: reducing the oil content and diluting the vinegar with other watery ingredients to provide more of the continuous phase without excessive acidity. Creamy but thin oil-in-water vinaigrettes can spread and cling reasonably well, and have the advantage over a cla.s.sic vinaigrette of being slower to discolor and wilt lettuce leaves. (Oil seeps through breaks in the waxy leaf cuticle and spreads into the leaf interior, where it displaces air and causes the leaf to darken and its structure to collapse.) Inventive cooks now make vinaigrettes with a variety of fats, including flavorsome olive and nut oils, neutral vegetable and seed oils, melted b.u.t.ter, and even hot meat and poultry fats (pork, duck); the water phase may contain vegetable or fruit juices or purees, meat juices or stock reductions; and the droplets may be emulsified or stabilized by thorough pulverizing to a small size in a blender, or with pounded herbs or spices, vegetable purees, mustard, gelatin, or cream. Today's vinaigrette is a very versatile kind of sauce!

Bottled salad dressings that look like vinaigrettes are generally stabilized and given body with starch or carbohydrate gums, which in low-fat versions can produce a slimy consistency.

Sauces Thickened with Bubbles: Foams Like emulsions, foams are a dispersion of one fluid in another. In the case of foams, the fluid is not a liquid, but a gas, and the dispersed particles are not droplets, but bubbles. Still, the bubbles do the same thing that droplets do in a sauce: they get in the way of water molecules in the sauce, prevent them from flowing easily, and thus give the sauce as a whole a thicker body. At the same time, they provide two unique characteristics: a large surface area in contact with air that can enhance the release of aromas to the nose; and a light insubstantiality and evanescence that offers a refreshing contrast to the texture of nearly any food they accompany.

There's one cla.s.sic foam sauce, the sabayon, which is made by cooking and whipping egg yolks at the same time to form a stable ma.s.s of bubbles. And both whipped cream and whipped egg whites can be folded with their bubbles into any water-based sauce. But cooks nowadays make foams from all kinds of water-based liquids and semisolids that contain dissolved