Culinary myths and legends of the white gold.
MYTHS ABOUT SALT DIE HARD. For example, some cooks recommend adding salt only to water that is already boiling because salty water, they say, takes longer to boil than pure water. This rule is widely believed, but is it justified?
Or consider the question of boiling meat to make stocks. Many cookbooks say that meat should be salted first in order to better extract its juices. Is the promised efficiency real or illusory? On the other hand, salad is not to be salted too far in advance because seasoning it in this way will wilt the leaves. What is one to make of this dictum, which comes from Japan?
With regard to vegetables, the French chemist Michel-Eugène Chevreul recorded the following observations in Recherches des matières fixes tenues en dissolution dans l’eau pure ou salée, qui a servi à la cuisson des légumes (1835): “Water used for the decoction of vegetables had a reddish-brown color; it retained a sensible quantity of the odiferous principles. Salted water used for the cooking of the same vegetables had a more pronounced fragrance than pure water; its flavor, allowance being made for the flavor peculiar to salt, was also more pronounced, and yet, remarkably, it contained a lesser proportion of extractive matter.” Is this account to be credited?
We should be wary of assertions that are not supported by sound experiments. With respect to the first claim, it is true that adding salt to water cools it down (because the water loses energy in dissolving the salt) and raises its boiling point and that the mass of fluid to be heated is greater. But whether salt is added before or after the water has been brought to a boil, all three phenomena are equally in play. If we heat water with and without salt (the same quantity of water, in the same pan, heated in the same way), we find that, within the limits of experimental error, the time needed to bring it to a boil is the same.
With regard to stock, it is commonly maintained that the major effect of salting the meat in advance is to promote osmosis. Heating causes the various molecules to move apart so that their final concentrations are everywhere the same, but because the larger molecules do not pass through the cellular membranes, it must be water that enters or leaves the cells, depending on the case. If one takes into account only this effect, one would predict as a theoretical matter that the meat must lose more juice when it is cooked in the presence of salt. Let us then conduct a simple but careful test. Put two identical pieces of meat in two identical pans, one containing pure water and the other water that has been salted to the saturation point. Now cook them for the customary five hours, weighing the two pieces every ten minutes. After the prescribed time has elapsed, the mass of the two pieces is the same, give or take a gram.
Would eggs react differently? It is sometimes said that the water used for cooking hard-boiled eggs must be salted because otherwise the water would infiltrate the eggs by osmosis, causing them to expand and to crack. Let’s cook a dozen eggs in a pan full of pure water and a dozen eggs in a pan identical to the first, filled with the same quantity of water, only this time highly salted. Again, let’s weigh the eggs at various stages of the cooking process to determine whether the suspected osmosis actually causes their weight to increase. Then we will count the number of cracked eggs in each batch.
Going to all this trouble is worthwhile because it reminds us of something that chefs knew in the nineteenth century but have forgotten since. Although salting the water does not prevent the shells from cracking (the best way to ensure that they don’t is to pierce the eggs with a needle, which by permitting the air trapped inside the egg to escape more easily preserves the integrity of the shell), it seasons the white of the egg, imparting flavor to an otherwise tasteless material.
Wilted Salad
Let us now turn to the effect of salt on vegetables. How do salad greens react when they are sprinkled with table salt? It turns out that there is no reaction, even after several hours, as long as the lettuce is dry. This is because its leaves are covered with a waxy cuticle that prevents osmosis.
What about vegetables cooked in water? To determine how much matter is lost during cooking, let’s experiment with onions and carrots, covering the pan and weighing them at intervals. Onions, it turns out, lose more of their mass when they are cooked for a short time in salted water. In this case the effects of osmosis are plain. With carrots, however, there is no great difference. In both cases the vegetables decompose more when they are cooked in salted water, but if the cooking goes on too long, they both wind up in the same degraded state whether or not salt has been added to the water.
Why do explanations that assume osmosis do a poor job of predicting the actual behavior of vegetables and meats cooked in water? A glance through the microscope gives the answer: Animal and vegetable cells are not covered with semipermeable membranes through which osmotic transfer can take place. Muscle cells are sheathed by collagen, and vegetable cells are protected by a rigid wall. Some degree of osmosis may occur at the beginning of cooking, but over time the structure of the cells is degraded, with the result that they open up and absorb fluid like a sponge. Salt doesn’t change anything.
There are many other such dictums. Putting cooked and peeled potato in a sauce that is overly salty, it is said, will remove the saltiness. Some chefs claim to be able to see tiny shimmering particles in sauces that have been oversalted. In the fourteenth century, Guillaume Tirel (known as Taillevent) noted that soups and stews tend to boil over if salt and fat are not added to them. In the case of grilled meats it is often said that salt should not be added at the beginning of cooking but reserved until the end so that it will be soaked up by the meat. To remove extra salt from a dish, Ginette Mathiot, author of the bestselling La cuisine pour tous (1955), advised immersing a cube of sugar in it for two seconds. What do you make of these recommendations?