Charak Samhita
अन्नस्य भुक्तमात्रस्य षड्रसस्य प्रपाकतः। मधुराद्यात् कफो भावात् फेनभूत उदीर्यते॥९॥
॥ Three states of digestion and provoking dosha॥ As soon as the food that has all the six tastes is consumed, it undergoes the first stage of digestion known as madhura (sweet) state during which kapha is produced which is like froth. Afterwards, while the food undergoing digestion is in its partially digested form, it attains amla (sour) state.
english translation
annasya bhuktamAtrasya SaDrasasya prapAkataH। madhurAdyAt kapho bhAvAt phenabhUta udIryate॥9॥
hk transliteration by Sanscript