Self rising flour and starter

I’ve read in a few places that you can’t use self rising flour to make sourdough starter, and I am curious if anyone can science me an explanation as to why. I’m trying to help someone who has fed their starter this kind of flour.

Self rising flour has salt and baking powder in it. Baking powder is made of corn starch and a mixture of a carbonate or bicarbonate and a weak acid.

Salt inhibits fermentation a bit, though we know it goes in most bread recipes, so it’s not deadly. How about baking powder? What would that do to prevent a starter from thriving?

Isn’t baking powder alkaline? And will prevent a starter from becoming acidic!

That’s just what popped into my head. Hope my science is correct.

Edit: ok just checked. Baking soda is alkaline. Baking powder while alkaline has the chemicals in it for the acid reaction it needs but only when it is heated. Does that sound correct?

Actually I think that’s wrong too :confused: oh dear. It becomes acidic when mixed with water. Can’t see why it wouldn’t work.

I think both the alkaline and basic components of baking powder dissolve when wet, and I’m reading that the pH of the solution is about 7.

You’re right that double-acting baking powder (most of what you see on the shelf) also reacts with heat, but I don’t think that impacts the pH.

Also reading that most flour has a pH of 6-6.8.

The person also uses well water, which can range up to 8.5. Bottled water would be about 7.

So many possibilities.

I once conducted an experiment and made a starter from scratch adding in 2% salt each time it was fed. Made a lovely starter. It was slow and steady instead of erratic like a “normal” starter can be at the beginning. So I can say for sure that by mistake adding a little salt won’t harm it. I’ve looked at the salt percentage in self raising flour and it’s within the usual limits. Whatever the case I think they ought not to worry.

I seem to recall that Gerard Rubaud always added a small amount of salt to his levain to inhibit protease enzymatic breakdown, so I agree, a modest amount of salt shouldn’t be a deal breaker.

Here’s the geek in me weighing in. If the baking powder (baking soda + cream of tarter) / baking soda combination act like a “pH buffered solution” when dissolved in the starter’s water, then I think they might try to keep the pH relatively constant (at that pH of 7 you mentioned), even as the starter is trying to produce lactic and acetic acids. My starter usually wants to sit at a pH of between 4 and 4.5 when mature. Therefore I am not sure how the baking soda/powder might affect the starter pH and its ultimate desire to create an acidic environment. Probably have to just try it and hope for the best.

Thanks @djd418 and @anon44372566 This is useful info, that the salt is fine but the pH buffering effect of the baking powder could be a problem. The person has been using self rising flour, and the starter has been unresponsive (well, it bubbled a bit, but even with patience etc nothing more ever happened) so I think we have uncovered this as the source of the problem. A relief to know!