I used cooked mashed potatos and some grapes and water for a starter yeast per instructions. Its active now with bubbles, but smells pretty bad (rotten), the equivilent smell of when a potato goes rotten and is mushy/liquidy. Is this okay? Been sitting for 3 days.
old-time homesteader yeast starter: 1 cup of cooked mashed potatoes, 1/4 cup sugar (i used grapes), 2 teaspoons salt ( i used no salt), 1 cup of warm water. Pour in to glass jar, cover with cloth, leave in warm area for two days or until ferments.
The smell of rotten potatoes is truly vile I feel for you there, I would throw the lot to be honest and start again using just flour and water and leaving it uncovered until it starts to ferment. Yeast fermentation won't smell bad so it sounds like you have some other bugs in there that you probably don't want.
Years ago I tried to capture wild yeast for starter. The first time it smelled gross and horrible. I tossed it, started again and the second time it worked fine and I kept it going for over a year until I lost it. Practice does help. My current sourdough has been going for about 4 years but I feed it rye flour and well water and I'm careful not to let it get contaminated. A friend brought it to me from Norway, so I'm extra careful with it - it's irreplaceable!
So I would try again - if it doesn't work a second time, I would consider trying a different recipe. Good luck!
If you're making that salt rising bread that's been going around lately, from what i understand it is supposed to smell cheesy and vile (not sure i'd want to eat something with that taste, but what do i know). But you need the salt to make sure you're not cultivating something even worse than the bacteria that makes the bread rise (Clostridium)....
I have made a bunch of levain and sourdough starters and a few times I've had them go off and had to throw them away. Normal is a bit sour smelling, rotten potato is definitely not normal.