best results would be to get the yst used to the new food. Feed it for about a week.
!/4 cup water and two big soons of flour/ stir. let sit. add water flour. let sit.pour some out. addwater flour, etc. Three times per day is best.
Keeping a bread starter is like keeping a pet. I kept one alive for three years.
This starter I've made twice succesfully; a bunch of grapes(pick out the bad ones but don't wash) plop into bucket (the whole bunch - handle as little as pos) and feed as above but more of both. After 4 days strain out the solids. Feed for another week. Voila' sourdough starter.` You will, of course, have to throw some out (the larger the starter the more you should feed it) or better, bake often.
When not baking, feed only once or twice per day. like a pet