Boiling is cooking foods by just immersing them in water at 1000C and maintaining the water at that temperature till the food is tender. Water is said to be boiling when large bubbles are seen rising constantly on the surface of the liquid and then breaking rapidly. Water receives heat by conduction through the sides of the utensil in which the food is cooked and passes on the heat by convection currents which equalise the temperature and become vigorous when boiling commences. Boiling points of water is 1000C and alter at high altitudes and in the presence of electrolytes.
When foods are cooked by boiling, the food should be brought to a vigorous boil first and the heat is then turned down, as violent boiling throughout tends to break the food. The temperature of the water cannot be increased any further after it begins to boil. Continued vigorous boiling results in excessive evaporation of water and waste of fuel and foods are likely to get burnt at the bottom and form a dry crust at the top.
Foods may be boiled in any liquid which is bubbling at the surface such as stock, milk, juices or syrups. Foods that are cooked by boiling are rice, eggs, dhals, potatoes, meat, sago and beetroot. Boiling can be done with excess amount of water (eggs, potatoes) or with sufficient water (dhal and upma).
Boiling is generally used in combination with simmering or other methods of cooking.
Ex. Cooking rice, vegetables or dhal.
- It is the most simple method. It does not require special skill and equipment.
- Soluble starches can be removed and rice grains are separated.
- Protein gets denatured, starch gets gelatinized and collagen gets hydrolysed.
- Uniform cooking can be done.
- Loss of nutrients: If excess water is used in cooking and the water is discarded 30-70% water soluble nutrients like Thiamine, vitamin C etc. may be lost. To prevent this type of losses, cooked water should be used in soups, rasam, sambhar and dhal. Some protein may be lost if vegetables are cooked in water containing salt and the cooking water is discarded. There is considerable loss of minerals especially sodium, potassium and calcium due to leaching.
- Loss of colours: Water soluble pigments, like betanin from beetroot may be lost. Beetroot should be cooked along with the skin to prevent the loss of colour.
- Time consuming: Boiling may take time and fuel may get wasted.
- Loss of flavour and texture: Boiled foods are not considered tasty because flavour compounds are leached into the water. Over boiling of food may make the food mushy.