There was recently a recall for certain flour, due to risk of salmonella contamination. The CDC announcement says not to cook with the flour. Naturally they are going to be conservative, and they might have in mind uses like cakes and cookies where flour is a major ingredient.
I don't know if my flour was from the affected lot (I no longer have the packaging), but every week I feed my sourdough starter and then bake with it, and I've fed it from that flour. To feed sourdough starter, you take a quantity of the starter and mix in more flour and water to keep the fermentation going. (And then you bake with or discard some of that, else the starter would take over the kitchen eventually.) Every time you feed the starter you "dilute" the flour you started with with new flour.
Can I safely dilute my existing starter through several feedings of safe flour and then use it, or is any amount of the suspect flour a health risk? Suppose I start with 25g of starter, feed it, discard half, feed it again, and do that a couple more times. I'd be down to a starter that contains only a few grams of the original. Is that safe? Or do I need to build a new starter from scratch (or get some from a friend)?
It's been a few weeks since I bought the flour in question, so I've already baked from it with no apparent ill effects, but I'm in pretty good health to begin with and some of my guests aren't. If there's a meaningful risk I'll toss it and start over, but maybe a couple grams of tainted flour in a loaf of bread is below the threshold where it could do harm. On the other hand, a comment points out that it's possible for the salmonella to multiply in the starter if the acidic environment doesn't kill it, so I'd still have larger quantities. I'm not a doctor, chemist, or culinary professional, and I don't know how to evaluate these possibilities.