In ‘kaRavaigaL’ pasuram, it is stated that ‘kaRavaigaL pinsenRu kAnam sErnduNbOm’. The cow herd boys who went along with Kannan for herding cows partook curd rice during lunch as per the puranas. It was a place where milk and curds were in supply and curd rice seemed to be a specialty for them. In memory of that, curd rice is offered; here ‘uNbOm’ denotes that we only know how to eat; the meaning conveyed here is that we do not know any other means, hence we perform sharanagati.
Traditionally during ‘undu madhakaLiTRan’, some do not offer tamarind rice; but it is a practice in certain places. This pasuram is very dearer to Bhagavad Ramanuja; to offer special food for this pasuram, tamarind rice might have been included.