The Four Basic Food Molecules - Chapter 1 : WATER

"Water is the major component of nearly all foods and of ourselves. It is a medium in which we heat foods in order to change their Flavor, Texture and Stability. "

Water is our most familiar chemical companion. It is the smallest and simplest of the basic food molecules, just three atoms; Hydrogen 2, Oxygen. Leaving aside the fact that it shapes the earth's continents and climate, all life, including our own, exists in a water solution. A legacy of life's origin billions of years ago in the oceans. Our bodies are 60% water by weight, raw meat is about 75%, fruits and vegetables up to 95%.

 "Our Ancestor was an animal which breathed water, had a swim bladder, a great swimming tail, an imperfect skull and undoubtedly was a hermaphrodite." - Charles Darwin, Darwin 1860, vol 8: 29

The important properties of ordinary water can be understood as different manifestations of one fact. Each water molecule is electrically unsymmetrical, or polar; it has a positive end and a negative end. This is because the oxygen atom exerts a stronger pull than the hydrogen atoms on the electrons they share, and because the hydrogen atoms project from one side of the oxygen to form a kind of V shape; so there's an oxygen end and a hydrogen end to the water molecule.

The oxygen end is more negative than the hydrogen end. This polarity means that the negative oxygen on one water molecule feels an electrical attraction to the positive hydrogen(s) on other water molecules. When this attraction brings two molecules closer to each other and holds them there, its called a hydrogen bond. The molecules in ice and liquid water are participating in from one to four hydrogen bonds at any given moment. However, the motion of the molecules in the liquid is forceful enough to overcome the strength of hydrogen bonds and break them; so the hydrogen bonds in liquid water are fleeting and are constantly being formed and broken.

The natural tendency of water molecules to form bonds with each other has a number of effects in the kitchen and also in our very lives.

Water is good at Dissolving other substances

Water forms hydrogen bonds not only with itself, but with other substances that have at-least some electrical polarity, some unevenness in the distribution of positive and negative electrical charges. Of other major food molecules, which are much larger and more complex than water, both carbohydrates and proteins have polar regions.

Water molecules are attracted to these regions and cluster around them. When they do this, they effectively surround the larger molecules and separate them from each other. If they do this more or less completely, so that each molecule is mostly surrounded by a cloud of water molecules, then that substance has Dissolved in the water.

Water and Heat

From Ice to Steam.

The hydrogen bonds among its molecules have a strong effect on how water absorbs and transmits heat. At Low temperatures, water exists as solid ice, its molecules immobilized in organized crystals. As it warms up, it first melts to become liquid water; and then the liquid water vaporizes to form steam. Each phase is  affected by hydrogen bonding.

Ice Damages Cells. Normally, the solid phase of a given substance is denser than the liquid phase. As the molecules' attraction for each other becomes stronger than their movements, the molecules settle into a compact arrangement determined by their geometry. In solid water however, the molecular packing is dictated by the requirement for even distribution. The result is a solid with more space between molecules than the liquid phase. Water expands when it freezes that water pipes burst when the heater fails in the winter or the container of leftover soup shatter in the freezer if they are too full for the liquid to expand freely.Raw plant and animal tissues are damaged when they are frozen and leak liquid when thawed. During freezing, the expanding ice crystals rupture cell membranes and cell walls, which results to loss in internal fluids when the crystal melt.


Liquid water is Slow to Heat Up.  Liquid water has a high specific heat, the amount of energy required to raise its temperature by any given amount. Water absorbs a lot of energy before its temperature rises; for example; It takes 10 times the energy to heat an ounce of water 1* as it does to heat an ounce of iron 1*. In the time that it takes to get an iron pan too hot to handle on the stove, water will have gotten only tepid. Before the heat energy added to the water can cause its molecules to move faster and its temperature to rise, some of the energy must first break the hydrogen bonds so that the molecules are free to move faster.

The basic consequence of this characteristic is that a body of water can absorb a lot of heat without itself quickly becoming hot. In the Kitchen, it means that a covered pan of water will take twice as long as a pan of oil to heat up to any given temperature and conversely, it will hold the temperature longer after the heat is removed.

Liquid water absorbs a lot of heat as it Vaporizes into Steam. Hydrogen bonding also gives water an unusually high "latent heat of vaporization", or the amount of energy that water absorbs without a rise in temperature as it changes from liquid to gas. This is how sweating cools us; as the water on the skin of our over-heated body evaporates, it absorbs large amounts of energy and carries it away into the air. Ancient cultures used the same principle to cool their drinking water and wine, storing them in porous clay vessels that evaporate moisture continuously.

Chefs take advantage of it when they bake delicate preparations like custards gently by partly immersing the containers in an open water bath, or oven-roast meats slowly at low temperatures, or simmer stock in an open pot. In each case, evaporation removes energy from the food or its surroundings and causes it to cook more gently.

Steam releases a lot of heat as it Condenses into Water. conversely, When water vapor hits a cool surface and condenses into liquid, it gives up that same high heat of vaporization. This is why steam is an effective and quick way of cooking foods compared with air heat at the same temperature. We can put our hand into an oven at 100°C and hold it there for some time before it gets uncomfortably warm; but a steaming pot will scald us in a second or two. In bread baking, an initial blast of steam increases the dough's expansion, or oven spring, and produces a lighter loaf.

Water and Acidity

Acid and Bases, Despite the fact that the molecular formula for water is H2O, even absolutely pure water contains other combinations of oxygen and hydrogen. Chemical bonds are continually being formed and broken in matter, and water is no exception. It tends to "dissociate" to a slight extent, with a hydrogen occasionally breaking off from one molecule and re-bonding to a nearby intact water molecule. This leaves one negatively charged OH combination and a positively charged H3O+ . Under normal conditions, a very small number of molecules exist in this dissociated state, something on the order of ten-millionths of a percent. This is a small number but a significant one, so significantly that humans have a specialized taste sensation to estimate its sourness.

Our term for the class of chemical compounds that releases protons into solutions, Acids, derives from the Latin Acere, meaning to taste sour. We call the complementary chemical group that accepts protons and neutralizes them, bases or alkalis.

The properties of acids and bases affect us continually in our daily life. Practically every food we eat, from steak to coffee to oranges are slightly acidic. The degree of acidity of the cooking medium can have great influence on such characteristics as the color of fruits and vegetables and the texture of meat and egg proteins. Some measure of acidity would clearly be quite useful. A simple scale has been devised to provide just that.

The standard measure of proton activity in a solution is pH, a term suggested by the Danish chemist S.P.L. Sorenson in 1909. It's essentially a more convenient version of the minuscule percentages of molecules involved. The pH of neutral, pure water, with equal numbers of protons and OH ions, is set at 7. 

A pH lower than 7 indicates an acidic solution while a pH above 7 indicates a greater prevalence of proton-accepting groups, and so a basic solution. The above diagram shows a list of common solutions and their usual pH.