We shouldn't cook acids, alkali and concentrated salts on teflon. But what are exact numbers? Can I put a sour dairy stuff for on it example, like kefir (it's good to put it in pancakes) ? Where is safe pH range?
We shouldn't cook acids, alkali and concentrated salts on teflon.
This is incorrect. Teflon (PTFE) itself is one of the most non-reactive substances you can use on cookware, in some ways better than ceramic. To quote Wikipedia:
It is nonreactive, partly because of the strength of carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals.
So why is there so much advice on not cooking high-acid foods in teflon pans? As far as I can tell, it's because teflon pans scratch easily, and acids can get into scratches. This has two potential effects:
- On pans with poor bonding between teflon and the backing metal, the acid can dissolve some of the adhesion between PTFE and pan, causing it to flake off.
- Many teflon pans have the teflon backed by aluminum, and aluminum gives off flavors to acidic foods. So even the small amount of aluminum exposed by the scratches can cause the high-acid food to taste "off", especially if it is slow-cooking.
Given the above, however, I think you can see that there is no specific pH that's bad for teflon pans. The lower the pH the worse the two above effects can potentially be, but a lot more depends on the manufacture of the pan, how scratched or abraded the teflon is, and even how long and how hot the food is in the pan. And if your teflon pan is brand-new and high-quality, it's one of the best vessels for making high-acid foods you have.
I don't know where your information came from about "We shouldn't cook acids, alkali and concentrated salts on teflon", but it is incorrect. Teflon is the least chemically reactive material you are likely to encounter in daily life. There probably are a few substances that can react with it, but if you have a way of sourcing these, you hopefully won't be asking about this on the Internet.
While I can't give you exact numbers, anything that you can eat is safe to use on teflon by a very wide margin. Go ahead and cook it.