Part 5 (2/2)
Can a Dish Containing Vegetables Be Reheated in b.u.t.ter?
Reheating vegetables in b.u.t.ter is often a mistake, because the b.u.t.ter will make the sauce oily, unless, by one means or another, the sauce has been emulsified as a precaution. Furthermore, if a dish contains sauteed vegetables, they will turn brown and dry out when reheated in b.u.t.ter. It is better to use water, in minuscule proportions, to compensate for the loss of the water involved in the initial preparation.
Of course, if a microwave oven is available, the problem of reheating is resolved. What a fine invention!
Why Must Cauliflower Not Be Overcooked?
The various vegetables in the cole family (mustard, brussels sprouts, cauliflower, broccoli, turnips, etc.) contain sulfur compounds, a.n.a.logous to certain aromatic precursors in onions. In these vegetables, however, the sulfur compounds are bound to sugar molecules and odorless as long as they do not come in contact with an enzyme that transforms them into aromatic compounds. This enzyme is inactive in the acidic conditions of normal vegetable tissues. But when the tissues are broken down, the enzymes come into contact with the odorant precursors, unbinding the sugar molecules and releasing the odorant compounds. The chemical weapon, mustard gas, is synthesized from such derivatives (which belong to the family of isothiocyanates).
The vegetables in the cole family were among the first to be a.n.a.lyzed because their strong, persistent odor when cooked suggested that they contained odorant compounds. Thus, beginning in 1928, it was discovered that the extracts of these vegetables, and their derivatives containing cystine (an amino acid), break down into various odorant compounds, especially dihydrogen sulfide, mercaptan, and methyl sulfide. Finally, these compounds react with one another to form trisulfides.
The longer the vegetables in the cole family cook, the greater the number of these molecules and the more the odor increases. Notably, the quant.i.ty of dihydrogen sulfide produced while cooking cauliflower doubles between the fifth and seventh minutes of cooking. The smell soon fills the whole house.
Choose your cooking time according to the degree of tenderness you desire for cauliflower, but do not go too far over that limit!
Why Do Beans Cause Flatulence?
Raffinose, a sugar present, for example, in peas and flat beans, is composed of a chain of three chemical rings, one fructose, one glucose, and one galactose. The table sugar that we eat, composed of glucose and fructose, is broken down by digestive enzymes into its const.i.tuent rings, which are metabolized. On the other hand, we have no enzyme capable of metabolizing galactose. It pa.s.ses intact into the large intestine where it is a.s.similated by the intestinal flora (especially the bacteria Escherichia coli Escherichia coli). The microorganisms of this flora release hydrogen, carbon dioxide, and methane. These are the three gases that inflate the stomach and produce those well-known noisy eruptions.
A good way to eliminate galactose from our vegetables is to let them germinate, because this process creates galactosidase, an enzyme that destroys galactose. They can also be soaked, and the water used for soaking and later that used for cooking discarded.
Sauerkraut and the Miracles of Fermentation We know that sauerkraut is produced by fermenting cabbage in a brine, where the development of certain pathogenic bacteria is blocked while the development of other organisms like Leuconostoc mesenteroides Leuconostoc mesenteroides and and Lactobacillus plantarum Lactobacillus plantarum is encouraged. During this development, the bacteria consume glucose and expel lactic acid, which gives sauerkraut its flavor. is encouraged. During this development, the bacteria consume glucose and expel lactic acid, which gives sauerkraut its flavor.
Lactic acid (C3H6O3) is half a glucose molecule (C6H12O6). It is formed through the anaerobic fermentation (in the absence of oxygen) of sugar and glucose, and it is responsible for muscle aches after sustained exercise when the muscles are deprived of oxygen.
Lactic acid is also found in milk when the milk is colonized by bacteria that make use of its sugar, lactose, and break it down, releasing lactic acid. By increasing the acidity of the milk, lactic acid makes it coagulate. That is how yogurt is produced. Similarly, lactic acid is responsible for the characteristic flavor of pickles and other foods preserved in vinegar.
How to make sauerkraut? It is remarkably simple. Shredded cabbage is placed in salt, and water is added to obtain a salinity of about 2.25 percent. At a temperature of 18 to 21C (64 to 69F), the bacterium Leuconostoc mesenteroides Leuconostoc mesenteroides grows and releases, in particular, lactic acid. Then, when the concentration of lactic acid reaches 1 percent, grows and releases, in particular, lactic acid. Then, when the concentration of lactic acid reaches 1 percent, Leuconostoc mesenteroides Leuconostoc mesenteroides is replaced with is replaced with Lactobacillus plantarum Lactobacillus plantarum. A good level of acidity is attained after about two-and-a-half weeks.
The Ripening of Tomatoes For the end of our journey, let us head toward the sun, with an examination of tomatoes, delicious but ephemeral. Initially green, they progress to a ripe state under the sun's heat, becoming juicy and aromatic ... but not for long, because they soon rot. Half the tomatoes produced, it is estimated, end up spoiling. What a shame!
Could their ripening be controlled, and their rotting avoided? Undoubtedly, because in general with tomatoes, ripening is preceded by increases in the respiration of the vegetable cells and the production of ethylene, a simple organic molecule that acts as a hormone.
T. Oller and his colleagues at the University of Albany have just demonstrated that ethylene is a cause and not an effect of ripening. In other words, one means of slowing down the ripening process in tomatoes consists of putting them in a very well ventilated place, so that they do not remain in contact very long with the ethylene they produce.
Sauces CREAMY, SATINY, FLAVORFUL.
Neither a Juice nor a Puree Before they sang of Trojan heroes or the adventures of Ulysses, the Greek poets invoked the Muses, who were supposed to ensure the truth of their poetic madness. As modern bard of one of the basic components of cooking-the sauces-I invoke Ali-Bab, that early-twentieth-century French engineer who, upon returning from his numerous world travels, offered gourmands the fruits of his long travel experience. His Gastronomie pratique Gastronomie pratique hardly merits its name, but his paragraph on sauces deserves to be quoted: hardly merits its name, but his paragraph on sauces deserves to be quoted: Sauces are liquid food combinations, thickened or unthickened, that serve to accompany certain dishes.Thickened sauces, by far the most important, all consist of a more or less succulent stock, seasoned, and a thickening agent. The number of stocks for sauces is considerable, the number of aromatics very great, and there are many ways to thicken a sauce. Thus, given these circ.u.mstances, it is easy to understand that, with the number of possible combinations being infinite so to speak, here lies a veritable gold mine for the treasure seeker.
What does this quotation teach us? That sauces are thickened to various degrees, but that, generally, a sauce is neither a juice nor a puree. With their highly sophisticated consistency, sometimes syrupy, sometimes creamy, always flavorful, sauces must have a certain quality to accompany fish, meat, vegetables, and desserts.
This precept is implicit in Ali-Bab's description. For sauces, the key words are ”consistency” and ”flavor.” If you examine various recipes for sauces that you have already made, you will see that these two basic elements are present every time: a flavorful liquid and a thickening agent.
If the question of flavor has come up in other chapters, the question of consistency, absolutely crucial, has hardly been mentioned until now. Two recent scientific findings, obtained by researchers in Dijon and Nantes respectively, will convince us of its importance.
First, in Dijon, Patrick Etievant, a physical chemist at INRA, offered tasting panels various strawberry jams in which differing amounts of jelling agents had been added in order to obtain varying degrees of firmness. The same batch of fruit had been used in all of them, and each of the test jams was a.n.a.lyzed for its chemical composition. Verdict: the firmer the jams were, the less flavor they had.
Second, at the INRA station in Nantes, Michel Laroche and Rene Goutefongea studied liver mousses in which, to make them lighter, they replaced part of the fat with a hydrocolloid, that is, essentially, a starch of water and flour. Once again a.s.sisted by taste testers, these two Nantes researchers discovered that the flavor quality of the liver mousses prepared in this way depended on the consistency. The more hydrocolloids the mousses contained, the more they melted in the mouth ... and the better tasting they were.
Thus not only do we expect a particular consistency from a particular dish, but the perception of flavors and scents depends on that consistency.
A Variable Consistency These remarkable findings of modern food science encourage us to a.s.semble the proper gear before taking off to explore the great land of sauces.
The notion of viscosity will be useful to us here. We have seen that a sauce is neither a juice nor a puree. Its consistency, or ”viscosity,” is somewhere in between. This entry point into the matter allows us to imagine how sauces can be spoiled in the hands of cooks who neglect the important principles. They may be too liquid, too solid, too inconsistent, too full of lumps.
Physics has shown modern gourmands that viscosity is a complex subject and therefore more interesting than they might otherwise have imagined. A few simple culinary experiments will clue us in to this new business.
First, let us dissolve sugar in water. As long as the amount of sugar is small, the solution flows like water, but when the syrup is concentrated, it thickens, sticks to the spoon, and flows with more difficulty. The proper equipment will show us that this viscosity, the inverse of fluidity, remains the same regardless of the speed of the flow: a constant shearing stress applied to a simple solution or a syrup generates a constant speed of flow.
For other fluids, such as mayonnaise, bechamel, and bearnaise sauces, the true sauces in short, this law no longer holds. In some cases, the viscosity diminishes when the speed increases; sometimes, on the contrary, the viscosity increases. Thus a bearnaise sauce that seems very thick, nearly solid when it is sitting in the sauceboat, takes on an angelic fluidity when it pa.s.ses through the mouth, at a speed of some fifty centimeters (about twenty inches) per second. Naturally, the molecular composition of the sauces is responsible for these flow properties.
And at this point let us retreat from our incursions into the territory of pure physics; we have enough gear to set out for the land of sauces.
Is Bearnaise Sauce Warm Mayonnaise?
With regard to mayonnaise, we have previously seen that water, perfectly fluid, and oil, also perfectly fluid, form a viscous mixture, thick enough sometimes to cut with a knife, if they have been combined in an emulsion, that is, into a dispersion of oil droplets stabilized with the help of the surface-active molecules of egg yolk.
The viscosity of emulsions is widely used in cooking. It accounts for the satiny quality of bearnaise sauce, hollandaise sauce, white b.u.t.ter sauce, and even of milk and cream, in which the quant.i.ty of fat dispersed in the water can be as high, respectively, as 4 and 38 percent.
Most of the time, sauce emulsions are of the oil-in-water variety. These are dispersions of droplets of a liquid fatty substance into a continuous phase of water. b.u.t.ter, on the other hand, belongs more to the water-in-oil variety (it is not a true emulsion, however, because part of the fat is solid).
Let us interpret the recipe for hollandaise sauce, of which the famous bearnaise sauce differs only in the seasoning and the quant.i.ty of b.u.t.ter dispersed in the aqueous solution.43 To make a hollandaise sauce, egg yolks are beaten, all by themselves, so as to mix their const.i.tuent parts thoroughly. Then water is added, lemon juice, and salt. The mixture is then heated (in a hot water bath if you are worried that your burner is too hot) and mixed to obtain an initial thickening. At this stage, the egg is forming microscopic aggregates, which add some viscosity to the emulsion. Finally, while whisking, b.u.t.ter is added bit by bit: the whisking separates the fat, which melts into microscopic droplets, and disperses them throughout the mixture, which is, in effect, a water solution. The sauce is removed from the heat as soon as it has thickened and served immediately.
What takes place during these successive operations? First, the surface-active molecules of the egg yolks have been dispersed in the tasty aqueous solution. These molecules are composed of proteins and lecithins.
Then, whisking the sauce while the b.u.t.ter melts separates the fat into droplets, which become coated with the various surface-active molecules already present in the mixture. At the same time, the protein coagulates, forming tiny aggregates that also become dispersed in the aqueous phase. Indeed, both hollandaise and bearnaise are not, strictly speaking, emulsions but rather share the attributes of two physical systems: emulsion and suspension.
Why Does Hollandaise Sauce Thicken?
Why does hollandaise sauce become viscous? Because it is a mixture more complex than pure water, and it flows with difficulty. Remember that it contains microscopic egg protein aggregates and fat droplets, which are bigger than the water molecules and mutually impede one another.
Another effect also takes place. First, the salt adds ions that link to the various electrically charged parts of surface-active molecules. Then, the lemon juice or vinegar causes the protein to become positively charged, which causes forces of electrical repulsion to appear between the egg aggregates and the droplets. All identically charged, the heads of the surface-active molecules repel each other. Their flow is further complicated by this repulsion; the viscosity increases many percentage points. But there is danger: if the temperature is too high, flocculation can occur, and egg protein aggregates can combine into bigger, visible aggregates. Lumps lurk: use your whisk!
Why Is Bearnaise Sauce Opaque?
To make an emulsion-hollandaise, bearnaise, or white b.u.t.ter-we begin with water, which is transparent, and b.u.t.ter, transparent as well when it is melted. Why is the resulting emulsion opaque? Because the light spreading through the sauce is reflected on the surface of the droplets, and it is refracted within the oil. The phenomenon is a.n.a.logous to what we observe when we put broken gla.s.s into a jar: the whole thing looks opaque, even though each individual piece of gla.s.s is transparent. Milk's whiteness and the yellow of a bearnaise sauce or mayonnaise result from this same phenomenon.
Why Do Some Emulsified Sauces Fail?
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