Part 6 (1/2)
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.