The science of ayurveda encompasses all aspects of life and cooking food is also one of them.
Of late, a lot has been written about food and prakruti. However it is just one aspect of ayurvedic cooking, and it too does not deal directly with cooking. It just states that which foods are good or which are bad for a particular prakruti.
As per ayurveda, any food which can be properly digested will not cause any harm. Therefore the aim of ayurveda cooking is to always make the substance as easily digestible as possible.
One can adopt the following methods to achieve this goal.
Warmth / Heat:
Food should always be as warm or hot as possible. Heat helps increase jataragni (digestive fire) which leads to proper digestion of food.
This does not mean that cold foods should not be consumed, but majority of food items should always be taken as warm or hot. Items like starters, appetizers, soups etc should always be taken warm, otherwise they will reduce the digestive fire, which is necessary for proper digestion.
Addition of Seasoning / Spices:
Seasoning and spices helps break down the food, thereby making it easier to digest.
People who have chronic complaints of indigestion, bloated stomach, acidity, constipation and other digestive disorders should never consume food which has not been seasoned or processed with spices.
Putting little ginger/cardamom to milk, black pepper powder or rock salt to fruits, proper seasoning of meat products using variety of spices / herbs is always advised.
Processing of Food:
This may seem like a little contradictory to the ayurvedic advice of eating as natural as possible, but not all natural foods are easily digestible. An apparent example would be the meat products. However, many vegetarian items too are equally hard to digest if eaten in their raw forms.
Make sure that cooking involves at least one process to make food easily digestible. Apparent processes would be boiling, steaming, frying, sautéing, seasoning etc. An easy example of processing would be the seasoning of items used in a salad.
Another good example of processing of food is ghee (clarified butter). Though ghee is prepared from milk, it undergoes nearly 3 processes, with each end-products being easier to digest than the former.
Milk (curdling) >>> curd (churning) >>> butter (heating) >>> ghee, the clarified butter
Avoid Contradictory Foods:
Ayurveda terms this as viruddha-aahar (viruddha means opposite, aahar is food).
There are several viruddha food items mentioned in ayurveda. These opposites can be taste opposites like sweets with bitter, potency opposites like milk which is of cold potency (sheeta veerya in ayurveda) and salt which is hot potency (ushna veerya in ayurveda), property opposites like dry foods with oloeus foods etc.
Mixing of opposite food items leads to formation of gara-visha (a type of toxic substance) which dampens digestive fire and disturbs digestion.
Fermentation of food items lead to the being endowed with guru guna (hard to digest property).
People with digestive problems should eat as less fermented products as possible. For others too ayurveda advocates use of such foods only in winter season (Hemant and Shishir ritu) when the digestive fire is at its maximum.
To sum up, actions which make food hard to digest should be avoided, and actions which make food items easier to digest should be adopted. This is the gist of ayurveda cooking.