Kitchen Mysteries_ Revealing the Science of Cooking Part 6

Hollandaise sauce, like bearnaise sauce, walks a thin line. To make it thicken enough, it must be cooked until the sauce almost turns. There are two opposing schools of thought regarding methods for salvaging a sauce that has turned. We will see that the complexity of the scientific problem is equal to the succulence of the sauce.

A hollandaise sauce can fail because the b.u.t.ter droplets melt together (they coalesce) or, worse still, because the aggregates produced from the egg yolk proteins form lumps. Coalescence is reversible, even if it is annoying, but coagulation is more serious. Some cooks claim that you can salvage a turned bearnaise sauce by removing it from the heat, adding vinegar, and whisking it very vigorously (with a mixer, for example). Others maintain that lemon juice works wonders, and still others claim that acidity has nothing to do with it. Adding a little water and whisking is all that is necessary for reprocessing a turned bearnaise sauce. What to believe? What to do in case of a disaster?

Let us think about this. In creating repulsion between the droplets, electrical forces keep them from rising to the surface and melting together, from coalescing. When the bearnaise sauce becomes too hot, however, the droplets move more and more rapidly, and they collide more and more frequently with increasing energy. The energetic barrier between the surface-active molecules is finally broken down, and the droplets coalesce. At high temperatures, the egg proteins coagulate irreversibly and form lumps.

Thus mastering the temperature is crucial. At high temperatures, the droplets collide very often and quickly, which promotes flocculation. Inversely, the difference between the surface tensions of the liquids increases at low temperatures, so the surface-active molecules have more difficulty forming emulsions.

The question, then, is how to strike the right balance and limit the phenomena that will destabilize an emulsion and possibly cause your sauce to turn.

Why Use Very Fresh Eggs?

The freshness of the eggs is important in preparing a bearnaise or hollandaise sauce because the lecithin molecules they contain are better surfactants than cholesterol is; as eggs age, their lecithin is broken down into cholesterol molecules.

In other words, the droplets of melted b.u.t.ter in a bearnaise sauce are better dispersed with fresh eggs than with eggs that are already old.

What Purpose Does Lemon or Vinegar Serve?

Lemon juice in hollandaise sauce and vinegar in bearnaise sauce give them a delicious, slightly acid flavor that perfectly balances the creaminess of the b.u.t.ter. These two acids are not there just for the pleasure of the tastebuds, however. They also ensure that the sauce stabilizes. Why does the acidity of the medium, which produces coagulation in milk, prevent it in bearnaise sauce? Because in the case of milk, the acidity acts on the proteins, whereas in a bearnaise sauce, it acts on different surface-active molecules. These surface-active molecules do not coagulate, and, better still, they retain their surface-active properties in conditions under which proteins coagulate: you can stiffen mayonnaise with a hard-boiled egg yolk!

Moreover, in warm emulsions, the acids break down the intramolecular bonds of the proteins so that the proteins can arrange themselves on the surface of the lipid drops and act as surfactants.

How Can We Salvage a Bearnaise Sauce?

Since bearnaise and hollandaise sauces are emulsions, a leading potential cause for their failure is a lack of water. As with mayonnaise, there must be enough water to accommodate all the droplets of that delicious melted b.u.t.ter that gives these sauces their remarkable satin-smoothness.

Since these sauces are prepared hot, the bit of water present in the sauce at the beginning of the preparation (as itself or in the wine, the egg yolks, the lemon juice or vinegar, or even the b.u.t.ter itself) can become insufficient for two reasons. First, when the proportion of b.u.t.ter becomes significant, it is the water-in-oil type of emulsion that is the most stable. Second, heated water evaporates. Even if you love wine more, do not forget the water!

In addition, if the melted b.u.t.ter droplets coalesce even though your proportions are correct, it may be because you have not whisked the sauce vigorously enough. Do not despair: quickly remove your bearnaise sauce from the heat, let it cool while adding perhaps a spoonful of water to increase slightly the volume of water where fat can disperse and then beat it very hard. You ought to be able to recover the creamy smoothness you lost.

The case of coagulated emulsions is a little more serious, but not desperate. When a sauce is overheated, the egg often coagulates into horrible lumps and the oil almost certainly separates from the aqueous phase. Once again, cool it as quickly as possible, and add a little cold water. Then use your mixer to break up the lumps by agitating the sauce. Sometimes this operation will save you the trouble of making the sauce over again. The proteins will remain coagulated, but the mixer will break them down into tiny invisible lumps ... except perhaps to the trained taste buds of a great gourmand.

Why Will Vinegar Repair Bearnaise Sauce?

We have seen that salt or acids (like vinegar and lemon juice) increase the solubility of proteins by breaking down some of their intramolecular bonds, improving their emulsifying powers while preventing them from coalescing by creating forces of electrical repulsion. If it is only insufficient mixing that has caused your bearnaise sauce to turn, adding acids and salt will certainly help recover a proper emulsion.

Vinegar may also work more simply, however, just because of the water it contains. Indeed, in certain cases, bearnaise sauce turns because the continuous phase (water) has become too thin. As with mayonnaise, the aqueous phase must be of sufficient quant.i.ty to accommodate all the droplets of melted b.u.t.ter. If there is too much b.u.t.ter, the water initially added becomes insufficient, and the oil-in-water emulsion tends to become a water-in-oil emulsion. Unfortunately, this inversion of the emulsion is often accompanied by a separation into two phases.

To avoid this inversion, remember that the egg yolk added to the sauce is only half composed of water; to provide sufficiently for the droplets of melted b.u.t.ter, add a little supplementary water (or vinegar or lemon juice).

When is there danger of the emulsion inverting? It is calculated that spheres all the same size can occupy, at the most, about 74 percent of cubic volume. By this hypothesis, the proportion of oil to the aqueous phase would be 3:1. The spherical droplets of melted b.u.t.ter in a bearnaise sauce are all different sizes, however, and they can change shape, so this ratio can be as high as 95 percent oil and 5 percent water.

The rule here is to consider that the sauce may need water; remember that, as you heat it, the water evaporates.

The Mystery of White b.u.t.ter Sauce Some cookbooks recommend, when making a white b.u.t.ter sauce, to reduce a little cream first before whisking in the b.u.t.ter. To understand this advice, let us recall that cream is an emulsion of the oil-in-water type, because there is a higher proportion of water in cream than in b.u.t.ter (which is a water-in-oil emulsion). By beginning with cream, to which b.u.t.ter is added bit by bit while whisking, the desired oil-in-water emulsion is obtained.

Emulsions in the Roast?

Before examining egg and starch as binding agents, let us remember that other sauces are emulsions as well. When you make a roast, for example, the fat drips from the meat into the pan at the same time as the juices, which contain some gelatin with surface-active properties. If you whisk together the fat and the juices (possibly adding a little b.u.t.ter at the end), you will obtain a bound, emulsified sauce.

Often when the roast is a bit overcooked, the water evaporates and only the fat remains. Add a little water or wine to obtain the quant.i.ty of water you need to make the continuous phase.

Likewise, when we cook a small beef fillet in a frying pan and deglaze with wine or some other kind of alcohol, we dissolve the caramelized juices in the bottom of the pan. And beyond that, if we want to show off like Moliere's Monsieur Jourdain in the kitchen, we can make an emulsion by adding b.u.t.ter or cream.

In these two cases, as for any emulsion, the physical composition is the same: continuous phase, dispersed droplets.

The Mysteries of Meat Glaze "Gelatin is a surfactant because, dissolved in water, it foams when it is agitated." Thus explained Madeleine Djabourov, physical chemist at the ecole de Physique et Chimie de Paris, when I asked her for advise regarding sauces. This remark gave me the key to gastronomy made easy; I pa.s.s it on to you.

Many sauces are prepared beginning with a stock: bouquet garni, pieces of bone with some flesh still attached, meat (or fish sc.r.a.ps, for fish stocks), first browned at a high temperature, and then cooked in water for several hours. That is the basic principle. I will pa.s.s over the skimming, reduction, and other fundamental but tedious details well covered in the cookbooks. To this stock is added an aromatic base and cream or b.u.t.ter.

What I have gathered from the preparation of these stocks is that they should serve as the base for preparing sauces, because they provide both the flavors and a binding agent. As proof, a stock reduced and placed in the refrigerator will form a colored, gelatinous ma.s.s.

Why are flavors and binding agents obtained in preparing a stock? Often we see that the prolonged cooking of fish and fish bones or meat, cartilage, and bones (calf's hoof is famous in this regard) causes the gelatin they contain to pa.s.s into solution. Vegetables contribute an indispensable aromatic note.

Since gelatin seemed to me to be the binding agent in sauces based on stocks, I wondered if the stock itself could be bypa.s.sed or at least made quickly by adding gelatin to a reduction of fortified meat juices.

This first experiment failed. To obtain enough viscosity, I had to add not one or two grams of gelatin but ten, twenty, thirty.... The viscosity was considerable when cold but weak when hot, and the sauce was disgusting.

Why this failure? Madeleine Djabourov's remark enlightened me. If gelatin is a surface-active molecule, then perhaps it is because of its emulsifying properties that it acts to form an emulsion....

In a new experiment, I used only a tiny quant.i.ty of gelatin, but I added b.u.t.ter to my sauce, which I whisked. It was a complete success, and my sauce was perfectly bound.

Not content with this success, I decided to take the experiment one step further, because sauces are the gourmand's poison: they make him fat and threaten him ... with gout and with dieting. Is it possible to retain the succulence of cla.s.sic sauces without adding all those delicious but harmful fatty substances?

To a certain extent, it is possible. To wine reduced with a few aromatics, I added gelatin and light cream (fat reduced by 15 percent). The latter, unsuitable for preparing sauces under normal conditions (it curdles), proved to be perfect, no doubt because of the large amount of gelatin present.

Binding with Egg Let us leave the land of emulsions to explore the land of sauces bound with egg. Indeed, we have already approached its border in considering bearnaise and hollandaise. Egg as a binding agent seems to have been discovered around the seventeenth century, but the principle behind it remains mysterious, if the method is simple enough: to a cold or lukewarm aromatic aqueous solution, add egg yolks and whisk them in while heating the mixture; gradually the solution thickens.

Done in this way, the preparation is delicate: if the sauce is not whisked enough or if it is heated too much, that is the end of its lovely viscosity, of the satin-smoothness provided by the eggs. Lumps appear; obviously the proteins in the egg yolk have coagulated.

Good cooks know how to avoid these lumps. By adding a pinch of flour to the mixture, they are able to stabilize the preparation so much that they can bring it to a boil without it turning. I advise the incredulous to try this experiment: using two identical saucepans, pour the same quant.i.ty of water or wine and add an egg yolk into each; whisk them identically, heating them in the same way; the only difference between the two sauces will be a pinch of flour, added to one saucepan but not the other.

The results are incontestable. The sauce that contains flour can withstand even boiling without coagulating. The other ... for the moment let us leave it to its sad, lumpy fate.

What is the effect of this minimal quant.i.ty of flour? Apparently the starch in the flour gradually dissolves in the sauce. Its long, very c.u.mbersome molecules seem to prevent the egg yolk proteins from aggregating while at the same time they contribute a viscosity a.n.a.logous to the one for which they are responsible in a bechamel sauce or in other sauces bound with flour.

Binding with Blood Similar to sauces bound with egg are those bound with blood. Blood contains many proteins, which, like those in egg, can establish networks that give a thickened texture to sauces.

That is the principle behind civet civet, a game stew prepared with mushrooms, red wine, and blood. The blood thickens the sauce, composed mostly of wine, a little vinegar, and all the aromatics. The same rules apply for binding with blood as for binding with egg: remember the little pinch of flour that makes all the difference!

How Do We Salvage a Turned Sauce Bound with Egg?

A sauce bound with egg turns when the proteins in the egg aggregate into macroscopic lumps instead of dispersing uniformly into microscopic aggregates throughout the sauce. Thus to correct such a disaster, proceed as for a bearnaise sauce in which the eggs have coagulated: a turn with the mixer will break up the lumps and recover the lost satin-smoothness. There is no guarantee, however, that the results will be as fine as if the sauce had been properly prepared. Chefs also filter the sauce through a sieve.

Binding with Starch Emulsification and binding with egg yolk or blood are not the only means for thickening sauces. Employing a roux or beurre manie thickener is equally efficient ... on the condition that you exercise good judgment. Misused, flour adds a characteristic, unpleasant flavor or can make for a slightly pasty consistency. All the same, let us be positive: before finding flour's faults, let us examine its benefits.

First of all, how should we use it? Often, a sauce begins with the preparation of a roux. b.u.t.ter is melted over low heat, then flour is added, and the mixture is cooked for a long time at a temperature just high enough to make it bubble. When the roux becomes golden or deep brown, depending on the sauce, a flavorful liquid is added, and the mixture is slowly heated. The sauce thickens and cooks. Finally, it is skimmed, that is, it is finished by using absorbent paper toweling to soak up the fat that has floated to the surface and by heating it at length to eliminate the solid particles and excess flour.

Why Does Flour Thicken Sauces?

To answer this preliminary question, we must know that flour is composed of proteins and complex sugars that form small granules we call starch. Complex sugars? What do we mean by that? Something very simple. First of all, glucose is a little molecule that serves as fuel for animals as well as plants. Produced by the effect of the digestion of foods, the glucose molecule is circulated through our bodies by the blood. Energy is easily extracted from it by our cells, and, conversely, the molecule is easily regenerated.

Plant seeds especially need energy to develop. Thus plants store glucose in their seeds. Since it is soluble in water, however, glucose on its own would be leached away by the first rain, so it is chained together in long, less soluble molecules, sometimes straight (like amylose), sometimes branched (like amylopectin).

Thanks to weak links between the amylose molecules and the amylopectin molecules, the latter aggregate into small starch granules, between two- to fifty-thousandths of a millimeter in size. In some places, these groupings are orderly and the granules are crystalline. In other places, the granules are amorphous and more fragile.

If starch is useful in making sauces, it is because, heated, the energy of the water molecules is enough to disturb the amorphous areas and establish hydrogen bonds between the starch molecules and the water molecules. Water is gradually introduced into the granules, which swell, forming gels called starch (beginning at 60 to 65C [140 to 149F] for wheat flour as amylose molecules leak into the water).

Why does this thicken the solution? Because the amylose molecules that have pa.s.sed into the solution are surrounded by water molecules, and also because the swollen starch granules become "microscopically enormous" and c.u.mbersome, making molecular motion difficult. The solution thus becomes viscous. And one final point: that viscosity is maximal when the temperature is kept between 79 and 96C (174 and 204F), not quite boiling.

Why Must Roux Be Cooked for a Long Time?

Amylose molecules have only weak thickening power and a floury taste. Thus, to avoid this taste, roux are cooked for a long time in b.u.t.ter before adding the liquid, to break down the amylose molecules into smaller sugars. Flour is an ideal product for the cook because it also contains proteins that react with the sugars through those Maillard reactions I have so frequently mentioned. Not only does cooking the roux eliminate the flour flavor, but in addition it produces odorant and tasty compounds.

If potato starch is used, the long cooking process becomes less important, because the amylose molecules, longer than those in wheat, have a less floury taste. Furthermore, potato starch jells at a lower temperature. It can be used to correct a too-fluid sauce at the last minute.

Why Must a Sauce Bound with Flour Not Be Overheated?

A sauce bound with flour must not be heated at too high a temperature, according to the cookbooks. After mixing the flour and liquid well, the preparation can cook but must not boil. Actually, once the sauce has attained its maximal viscosity, at about 93C (199F), it will reliquefy a bit if it boils.

Many conditions favor this reliquefication: heating for a long time after thickening, heating to the boiling point, and too vigorous physical agitation. In all these cases, the swollen granules are broken up into small fragments that flow better than large ones. In addition, a greater quant.i.ty of amylose then pa.s.ses into the solution. A network composed of a greater proportion of amylose is less rigid than one that is princ.i.p.ally formed from amylopectin, and the granules are less well maintained.

Why Must Sauces Bound with Flour Remain Liquid While They Are Cooking?

As a sauce bound with flour cools to below 38C (100F), the dispersed granules, already further separated by the amylose, begin to form a gel. When the mixture is cooled, the water and starch molecules have less and less energy, and hydrogen bonds begin to hold the molecules more and more securely, eventually reestablis.h.i.+ng those bonds that were initially responsible for the cohesion of the granules. The liquid hardens.

This effect should inspire cooks to make their roux-based sauces thinner than optimal for serving at the table. By the time they reach the table, they will inevitably have cooled and thickened.

The Skimming Skimming is a refined operation. It is the elimination of solid particles in the sauce (see the chapter "Cooking"). Sauces bound with flour, especially, are improved by skimming off some of the solid particles of starch or the lumps formed during the sauce's preparation, as well as the flour proteins, which are not soluble in water. During the sauce's preparation, these proteins coagulate into little solid blocks that must be removed to achieve a perfectly uniform result worthy of Careme and the other great masters of French cooking.

If the famous French cook August Escoffier wanted manufacturers to introduce a gluten-free flour, it was specifically to avoid this long skimming operation. He was not entirely justified, because Maillard reactions, which require proteins, occur during the skimming and also because proteins cooked for a long time are dissociated into sapid amino acids.

In practice, a sauce is skimmed while it is heated, after it has been filtered, in a saucepan tilted in such a way that only one point on the bottom receives heat. Above this point, the sauce is hotter than elsewhere and thus lighter. It rises, and a current is established, with a plume ascending in the center and re-descent occurring on the periphery. As this happens, the solid particles follow the current but have the tendency to gather at the center of the saucepan and clump together. They only have to be skimmed periodically to eliminate them.

How Do We Salvage a Sauce that Is Too Thick or Thicken a Sauce that Is Too Thin?

Is the sauce you bound with flour too thick? Beat it vigorously, keeping a close eye on its viscosity. In this way you can break up the swollen granules until the sauce achieves a good consistency.

On the other hand, what to do if your sauce is too fluid? I can recommend beurre manie, a thickener of b.u.t.ter and flour worked together but not cooked. These two ingredients are mixed in equal amounts, and a little ball of the preparation is added to the sauce. The b.u.t.ter keeps the flour from lumping, so that it is gradually released into the sauce. This procedure is only a stopgap measure, however, because it does not avoid that floury taste. Thus it is a good idea to make your beurre manie from corn-rather than wheat-flour.

Why Must Some Fatty Substance Be Used in Sauces Bound with Flour?

Fats do not affect the viscosity of sauces bound with flour, but they affect the impression the sauce makes in the mouth. And, during the preparation of a roux, they coat the flour particles and keep them from lumping in the added liquid. Although their quant.i.ty can be limited, it seems difficult to eliminate them entirely.

Why Must Lemon Juice and Vinegar Be Avoided in Sauces with a Roux Base?

If lemon juice or vinegar are heated in the presence of amylose and amylopectin chains, they break down these chains into shorter ones that bind less well with water. The starch granules then gel and disintegrate at lower temperatures. For any given quant.i.ty of starch, the final product is less viscous.

A Burning Question Let Us Eat Well, We Will Die Fat Why do we like hot pepper, which burns? How can what is good be bad? Before turning to the pepper itself, let me enlarge on the question it poses for us: Is eating harmful?

Brillat-Savarin devoted a few juicy pages to the excesses of dining. Remember, this is his second aphorism: "Animals feed themselves; men eat; but only wise men know the art of eating."44 And his tenth: "Men who stuff themselves and grow tipsy know neither how to eat nor how to drink." And his tenth: "Men who stuff themselves and grow tipsy know neither how to eat nor how to drink."45 Very well. So eating or drinking too much is harmful. Today's doctors even try to specify which foods to avoid: certain animal fats, carbon and products of excessive combustion, nitrites used to salt meats ...

Nevertheless, the danger they see is truly everywhere. Chemists who study Maillard reactions (see page 27, for example), those universal reactions in cooking, find that they produce dangerous compounds of all kinds, and biologists are discovering that amanitoidin, the toxin in the white fungus phalloid amanita, is present in chanterelles and in most other edible mushrooms, though in minute quant.i.ties. We must conclude that the harm is in the excess, that it is the dose that makes the poison.

Does Hot Pepper Burn a Hole in the Stomach?

On the other hand, are the foods that seem harmful really harmful? Pepper, for example: is it as harmful as its effect on the tongue and mouth would lead us to imagine? A burning question that has, finally, just been studied empirically by doctors. David Graham, at the Veterans' Medical Center in Houston, Texas, used endoscopy to observe the effects of hot pepper on the stomach lining of twelve volunteers. He looked for possible inflammations after the absorption of meals peppered in various ways by lovers of highly spiced dishes.

During the first experiment, the volunteers were given a "neutral" meal, consisting of steak and french fries. Then, on another day, they ate the same meal, but seasoned with aspirin (which has a reputation for puncturing the stomach). Finally, on a third occasion, pizza with spicy sausage and various Mexican foods were prepared for them, to which the medical team added as much hot pepper as most people can tolerate.

Endoscopy revealed that aspirin did indeed attack the stomach lining, but that hot pepper had no visible corrosive effect.

The princ.i.p.al pungent ingredient in hot pepper is capsaicin, a phenolic amide C18H22NO2 (or 8-methyl-N-vanniyl-6-neneamide). It stands to reason that this was the first ingredient to be studied. Its effect on the intestinal wall was compared to that of aspirin. Capsaicin had no visible effect. Neither did crushed red pepper deposited directly into the intestine with the help of a cannula. (or 8-methyl-N-vanniyl-6-neneamide). It stands to reason that this was the first ingredient to be studied. Its effect on the intestinal wall was compared to that of aspirin. Capsaicin had no visible effect. Neither did crushed red pepper deposited directly into the intestine with the help of a cannula.

On the other hand, Tabasco sauce deposited directly into the stomach produced an inflammation of the stomach lining. Why? Because it contains acetic acid; vinegar is a solution of acetic acid in water. In fact, the concentration of acetic acid in Tabasco is two times higher than the concentration of acetic acid in ordinary vinegar.

Thus, if red peppers stimulate nerve endings that register pain, especially in the mouth, they do not have an actual corrosive effect. They stimulate salivation, activate digestion, cause burning sensations in the a.n.u.s, and provide a feeling of well-being after a meal. Why? Perhaps because they stimulate the release of endogenous opioid substances, similar to morphine in their effect on the pain-sensitive nervous system.

So let us no longer be afraid to use hot pepper. Its fire will not consume us.

The Salad AN OASIS OF FRESHNESS.

Should the Salad Be Prepared in Advance?

Salad, with the vinaigrette that accompanies it, is a dish that the gourmand has never managed to fall in love with completely. It is a delicate, refres.h.i.+ng, and welcome complement to a big meal, but it "kills" the wine because of its acidity. If you serve salad, give your guests only water to drink with it, and change mounts, as riders say, for the cheese and dessert courses. The salad interlude requires that a completely different wine follow the one you served with the meat.

How should a salad be prepared? We all think we know how: you wash the salad, add a vinaigrette dressing, and toss it.

Not so fast! Did you know that if you are serving a mixture of many different salad greens, you would be well advised to toss the toughest varieties first and then add the tender varieties? Did you know that the vinaigrette should not be added before you are ready to toss the salad? Did you know that vinaigrette is a different dressing depending on if there is more or less oil?

Vinaigrette Let us begin by examining the composition of the vinaigrette. We have seen with regard to mayonnaise that we achieve a mixture of oil and water by forming an emulsion, that is to say, a dispersion of oil droplets in water or, conversely, a dispersion of water droplets in oil. Composed of vinegar, oil, salt, pepper, and mustard to taste, a vinaigrette is just such an emulsion. The vinegar is a solution of acetic acid in water; the oil is ... the oil.

Normally, oil does not dissolve in water. It is only when a mixture of oil and water is vigorously agitated that the oil droplets achieve a suspension in the water. And this is only temporary, moreover, because these droplets, which are lighter than water, rise again to the surface, merge, and reform a separate oily phase.

Nevertheless, if the oil droplets are small enough, their separation is slowed, because their dispersion hampers the rising process. In addition, the mustard in vinaigrettes increases the stability of the emulsion: whisked into the vinaigrette at the same time as the oil droplets, its surface-active molecules bind to the oil molecules along their hydrophobic extremity and to the continuous, aqueous phase along their hydrophilic extremity. They thus form a link between the oil and the water.

This description only applies as long as the proportion of oil is not too great. When the water and oil are present in equal quant.i.ties, the oil forms droplets that disperse in the water because it has the tendency to form droplets. On the other hand, if the proportion of oil is increased, it is the water that will be dispersed in the form of droplets in the oil. In the presence of mustard, this transition takes place when the proportions exceed two parts of oil to one part of water.

In any case, these emulsions are more transient than a mayonnaise emulsion. Left to itself for a little while, a vinaigrette separates into vinegar at the bottom and oil on top.