Vipaka is a unique concept of Ayurveda. It is the post digestive effect of any ingested substance.
These can be in either of the two forms:  Ahara dravya (food) or Aushadh dravya ( medicine).

Once the digestion of these substances takes place in the gastro-intestinal tract, it is metabolized and transformed into an absorbable form which is called Vipaka.
In general understanding Vipaka is the final bio-transformation of digested food/drug.
The term “Vi” (of Vipak )  is ‘Vishishta’ means specific or special, and “Paka” refers to digestion or the function of Agni (digestive power or biological power ).

Any substance when ingested, it is digested and metabolized by the action of different specific Agnis (biological fire)  i.e., Jatharagni, Bhutagni, and Dhatwagni  of the body. During the entire process, the ingested substance decomposes and re-synthesizes several times for further absorption and assimilation process .  This can also be referred to life experiences.

According to one of the greatest scholars of Ayurveda, Acharya Charak, ‘Vipaka’ is referred to as “Karma Nishthaya”, which means the vipaka of any herb could be defined by the karma (action) of that particular herb (food/drug). It determines the specific action of the food/drug on the doshas of the body. He explains that the six rasas (the basic constituents of any substance) further produce three kinds of Vipaka i.e. Madhura, Amla and Katu, which determines the specific action of that herb on dosha, dhatu and mala. The relation could be related as below :
1. Madhura vipaka (sweet) - Madhura and Lavana (salty) rasa dravya produces madhur vipaka. 
2. Amla Vipaka (sour) - Amla Rasa dravya produces amla vipaka.
3. Katu Vipaka (acrid, pungent) - Katu, Tikta (bitter), Kasaya (astringent) Rasa dravya produces katu vipaka.

However, one must remember that it is not necessary that all rasas produce similar corresponding vipaka.  Depending upon the usage or combination of the food/drug, the Vipaka may differ.  A Katu rasa food may result in Madhura vipaka. Therefore, an understanding of the interaction of different foods/ drugs substances while pairing of food is important.

The tentative action of different types of Vipaka could be :
1. Madhura Vipaka
- Increases the kapha
- Eliminates the excreta (urine & stool)
- Increases the shukra dhatu (Reproductive potency)

2. Amla Vipaka
- Increases the pitta
- Eliminates the excreta (urine & stool) smoothly
- Decreases the shukra dhatu (Reproductive potency)

3. Kaṭu vipāka   
- Increases the vata
- Suppresses the excreta (urine & stool)
- Decreases the shukra dhatu (Reproductive potency)

In view of the foregoing it could be concluded that Vipaka plays a very major role in digestion and post digestion processes in the body.
An understanding of ‘Vipaka’ is most useful to pair your foods well while we eat or cook our meals. In today’s time, this understanding has taken a back seat, and due to poor pairing of foods and beverages ( due to the incompatible nature of the foods) two contradictory ‘vipaka’ impact digestive processes negatively leaving you with issues of gas, bloating, acidity, and more. If such incompatibility persists over longer periods of time, it could result in diseases such as Vitiligo.