I am on the 4th day of the great pineapple starter and everything went as planned!  My question is why to throw away all but l/4 of the starter and add flour and water?

 Am I suppose to throw away all but l/4 of the starter everytime I feed it?  Could I keep the throwaway and start another batch?  Sorry if I am naive but am new to this wonderful event!!! Thanks so much,

Nonna