You don't have to cook fancy or complicated masterpieces - just good food from fresh ingredients. - Julia Child
If there is one good thing about the lockdown during the pandemic, it is that people had enough "me time". A world with social distancing and no schools, colleges, or work gets pretty lonely. With extended hours on hand and restaurants being shut down, cooking and baking at home had been one of the many activities that people had resorted to. People have actually developed an appreciation for cooking and have worked on improving their skills. Like many others out there, I have also started to binge cooking shows on Netflix, and try out the various recipes found on the internet. In this series, I am going to explain a few terms and techniques that will help you all appreciate cooking better.
The discovery of fire certainly changed our ancestors' lives for the better. The ability to control fire was the starting point of the technological evolution of humankind. Humans had been hunters, and the fire gave them warmth and protection from predators. It also helped them make better weapons for hunting. Yet, the best thing that came out of the fire was Cooking.
Cooking is nothing but the technique that uses heat to "prepare" food for consumption. Preparing food with heat is an activity unique to humans. Heat makes food softer, and this means less time for chewing. It also makes food more easily digestible and helps us better absorb the nutrients. Most importantly, cooking destroys any microbes or toxins that may be quite harmful to us.
The phenomenon of "heat transfer" refers to the exchange of heat between two objects by virtue of their temperature difference. In cooking, the heat is transferred from the cooking appliance to the food. Heat transfer can take place by three processes, namely, conduction, convection and radiation.
Conduction
Conduction is the most common mode of heat transmission in cooking where the food is in direct contact with either the cooking appliance (that is in contact with the heat source) like a pan/cooker or in contact with an intermediate medium like hot water or oil. The cooking rate is relatively slow, and the food is cooked from the outside.
Convection
Convection is a heat-transfer technique that employs the circulation of air or liquid to cook the food. In a convection oven, the air is heated, and it moves towards the colder food and warms it up. When we stir a liquid food in a pot, the heat is evenly distributed throughout.
Radiation
Radiation is a heat-transfer technique that involves no contact between the source of heat and the food. It employs heat waves such as Infrared (broilers and toasters) or microwave (microwave oven) to heat the food by penetrating and heating it from within.
What happens to the food when we are cooking it? To understand this, let us first break down food into five basic components - water, proteins, sugars, starch and fat. Each of these components behaves quite differently when exposed to heat. A good understanding of heat transfer and how food reacts the way it does when it’s heated up helps us better understand the whole cooking process.
Water
We are all well aware of how water behaves upon heating; it gets converted to steam (water vapour) and leaves the food. Cooking is generally associated with water or water-based fluids. Either the food item contains water in it, or it is immersed in a liquid (stock, water, or wine) while cooking. Water has the highest specific heat capacity for a liquid, i.e., the heat required to raise one gram of water by one degree Celsius. This results in water having numerous roles in cooking.
Water "nearly" maintains the temperature of the food even while being heated slightly over extended periods. Raw foodstuffs like rice or pasta have to be cooked in water to be edible. When excess water in syrups, sauces and gravies is allowed to evaporate, it results in the concentration of flavours in the "reduced" liquid. Simmering vegetables or meat in water helps extract the flavours, and this resultant stock forms the basis of a soup or a stew. Steaming, a moist-heat method utilizes steam as a heat-carrier for cooking the food. Steam also creates high pressure in a closed vessel, and this speeds up the cooking process, as in the case of a pressure cooker. Boiled water also acts as a flavour carrier in beverages such as tea, coffee and lemonade.
Proteins
Proteins are composed of amino acids - organic compounds made of carbon, hydrogen, nitrogen, oxygen and sulfur. Protein provides food with structure and texture and enables water retention. When a protein is cooked, the added heat results in the change in the structure of the protein, from a liquid (or semi-liquid) to a thicker liquid or solid. This process is known as coagulation. Cooking a protein enables the amino group present in them to bind with the carbohydrates, thus creating aroma.
The most common example of coagulation by heat is the cooking of an egg - omelettes, boiled egg, scrambled eggs, etc. In this case, it is the protein Albumin that coagulates. In the production of "fresh" cheeses like Paneer, Ricotta, and Queso Blanco; Casein proteins and Whey proteins coagulate when a heat-acid treatment is used.
Sugar
All sweet and water-soluble carbohydrates can be called as sugars. Sugar is found naturally in many nutritious foods, such as fruits and vegetables in the form of Galactose, Glucose, Fructose, Lactose, and Sucrose. Other than these natural sugars, there are many more artificial sugars that are added to food to enhance the taste. When heated, sugars such as Lactose and Sucrose break into their constituent monomers like Galactose, Glucose, and Fructose. Further heating of the sugars results in dehydration and other chemical reactions. The sugar turns brown and begins to release the flavour in the food. This process is known as caramelization.
Starch
Starch is a soft white powder that is both odourless and tasteless. It does not dissolve in any solvent barring hot water. Starch is a carbohydrate that is made up of numerous glucose molecules that form a polymer. When starch is heated in the presence of water, it undergoes a process known as gelatinization. The polymers in starch lose the intermolecular bonds, and this allows them to bind to the water molecules that are absorbed in the spaces between them, leading to swelling. When the water is cold, the molecules of water cannot diffuse into the spaces. Heating gives the water molecules enough energy to diffuse and also assist the bonds of the polymer in breaking.
This process is well realized in the cooking of rice and pasta in boiling water. Small grains of rice and uncooked pasta absorbs the water and increase in size and softens. In sauces and soups, starch is added while cooking. This starch absorbs liquid and swells, resulting in the thickening of the liquids.
Fats
At room temperatures, fats like butter, ghee and oils can be in a solid, liquid or an intermediate state. Upon heating, fats just melt into a liquid. They have very high boiling points and smoking points (the temperature at which any substance smokes or burns). This helps them blend ingredients and enhance the flavour of the food. Fats are thus used as a cooking medium rather than ingredients.
Whatever be the kitchen appliance we use, heat transfer is the basis of its functioning. Understanding what type of heat transfer is employed, and how it affects the ingredients helps us better appreciate cooking and improve our skills as amateur chefs. Various cooking techniques that involve conduction, convection and radiation shall be discussed in the next part of the series.