Not sure what you mean by "high grade flour". You'll get the best results with specified "bread" flour, but "all purpose" flour will work fine, too. Do not use "cake" flour.
It is not the bread that is refined but the flour that the bread is made with - thus a sourdough bread can be made with unrefined flour or refined flour.
I have checked out two brands of sour dough bread still available. San Louis Sour Dough Bread, I found the sour dough taste to be slightly stronger then Colombo. I actually prefer this San Louis Sour dough ov3er Colombo, so this has soften the blow of losing Colombo Sour Dough Bread. The one bread that came in a close second was Boudini Sour Dough Bread. The sour taste was not as strong as San Louis. Beware of a lot of sour dough imposter's, if it looks like white bread, it is!!!!!!
Rice bread is gluten-free, but it could be cross-contaminated.
Yes, sourdough bread has a slightly tangy or sour taste due to the fermentation process that creates natural acids in the dough.
Neither is great, but of the two, whole wheat would be better. It is a little harder to breakdown into sugar so you will not spike quite as much or as quickly. Actually I've hear quite the contrary. Sourdough bread is sour due to lactic acid released by the bacteria fermenting in the dough. The lactic acid is what keeps the blood sugar from rising.
A fermentation process.
Sourdough bread is sour because of the presence of lactic acid bacteria in the dough. These bacteria ferment the sugars in the flour, producing lactic acid, which gives the bread its tangy flavor. This fermentation process also helps to break down gluten in the dough, making the bread easier to digest.
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Sourdough bread is sour because of the presence of lactic acid bacteria in the dough. These bacteria produce lactic acid as they ferment the sugars in the flour. This lactic acid gives sourdough bread its unique tangy flavor.
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By washing regularly.