Yep, I made my first article on a cooking blog about one of the simplest of all techniques. This whole subject created a stir when a very popular cooking site posted a recipe for boiling water. The jokes were many; however, there is more to it than putting a pan of liguids on the stove and turning the burner on.
Boiling
Boiling is used for pastas and some vegetables. Boiling water is 212° F at sea level. The liquid will have many bubbles bursting all over the surface, and a steady cloud of steam is visible. For a brief science lesson, heating water causes the water to turn to a gas, and the bubbles are the gas rising to the surface. The temperature of boiling water varies based on the elevation. A decrease in atmospheric pressure causes a lower boiling point because it takes less energy for the gas to form. Water may boil at 200° F rather than at 212° F, for example. According to FSIS, each 500 feet increase in altitude causes a drop of about 1° in the boiling point of water. Turning up the burner will not increase the temperature of the liquid. Once a liquid has reached its' boiling point, the liquid changes to steam so turning up the burner will only cause the water to evaporate faster. Because the liquid is cooler, the cooking time will need to be increased to get the food completely cooked. A recipe that states to cook for 10 minutes may take 12 or more minutes to cook. The cooking time may increase from 4 to 11 percent depending on the food. The boiling point of other liquids may vary from that of water, but the same effects caused by elevation occurs.
Simmer
Not all foods are best when cooked at a full boil. Meats cooked at boiling temperatures will become dry and flavorless. The best temperature to cook meats, stews, most beans and many vegetables are at a simmer. A simmer is described as small bubbles rising continuously to the surface. In Chinese tea brewing, the bubbles are described as a rope of pearls. A steady stream of pearl size bubbles. The temperature is between 190° F to 200° F at sea level. This is the temperature slow cookers cook at or should cook at. Covering the pot you are simmering food in will increase the temperature inside the pot and may change a simmer to a boil. At higher elevations water evaporates quicker than at sea level and water levels in the pot need to be watched. An occasional large bubble should not be a problem unless the liquid is thick, then the burner needs to be turned down to prevent scorching. Dishes containing meat or eggs need to be tested using a thermometer to determine if the internal temperature has reached safe levels.
Poaching
This is the temperature used for poaching fish, eggs and fruit. The gentle movement of the cooking liquid prevents the food from getting torn apart. This is the most debated of all moist heat cooking temperatures. Some cooks have poaching as a reduced simmer while others use much lower temperatures. I personally prefer the lower temperatures of between 160° F to 180° F. The high level used by some cooks is 190° F which is the same as the lower level of a simmer. You should be able to see the water moving in your pan, but bubbles should be scarce and small.
Sous vide
Sous vide is a method used by chefs who vacuum seal food in a bag then places the bag in a circulating, thermostatically controlled water bath that is at the same temperature as the desired end temperature of the food being cooked. For example, fish would go into 140° water. The food is then slow cooked up to seventy-two hours-depending on what is being cooked and the size of the item. This method results in very tender meat. However, home cooks do not have the specialized equipment required to use this method safely at home. Alot of ugly organisms can grow in the anaerobic environment inside the vacuum sealed bag. Some companies are developing at-home appliances. Until then, do not attempt to hack your crock pot or use other methods you may see on the internet that describe how to do souse vide at home.
Other factors that may influence boiling point
Salt may increase the boiling point by 1° F. This change has a barely noticeable effect on cooking times. Sugar-another soluble-has a noticeable effect when used in heavy sugar solutions. Soluble minerals found in hard water may also increase the boiling point one or two degrees. High humidity on stormy days will reduce the boiling point by a degree or two.
If you are interested in Cooking Science, you may enjoy NASA's boiling water lab experiment. Did you know Galileo used boiling water to estimate altitudes?
For more information on cooking with water see:
Making Hard Cooked Eggs
Cooking Technique: Moist Heat, Simmering
Cooking Techniques: Moist Heat, Poaching
Cooking Techniques: Moist Heat, Boiling
