Are you sure that the Mexican flours such as you showed in the photos are bromated? Recently, when I was working for Norma on the Ultra-Thin project, I researched bromated all-purpose flours in the U.S. and could not find any such product. I even had a couple of exchanges on this matter with a specialist at General Mills. For example, see Reply 360 at http://www.pizzamaking.com/forum/index.php/topic,11044.msg102978.html#msg102978
Moreover, every time that I go to Mexico I make a point of it to scrutinize Mexican flours and labels. I don't ever recall seeing bromates (potassium bromate) on the labels. Both of the brands you mentioned, and showed in your photos, are usually available in the markets near me outside of Dallas. This morning, while I was at a local supermarket that caters mostly to Hispanics, with many brands of food items that I have seen in Mexico, I did not see the San Antonio brand but I did see the Selecta brand. I jotted down the ingredients, exactly, as follows: Enriched Flour wheat Iron, Folic Acid, Niacin, Benzoil Peroxide, L-ascorbic Acid, Azodicarbonamide and Enzymes.
In this listing, the benzoil peroxide is a flour bleaching agent. L-ascorbic acid is Vitamin C and is frequently used as a substitute for bromates (e.g., Papa John's in the U.S. does this). The Enzymes are most likely diastatic malt, either in dry or fungal form (fungal amylase). The Azodicarbonamide is a dough improver, used to mature and bleach the flour. It apparently is outlawed in many countries, including Europe. It is possible that the benzoil peroxide and/or the Azodicarbonamide are deleterious to natural sourdough cultures. For example, I have read that one should not use bleached flours to feed sourdough cultures. However, I don't know if that is an old wives tale or is backed by good science.
I don't have an empty San Antonio Tres Estrellas flour bag to examine more closely, but according to the ingredients listing given at http://www.mexgrocer.com/13522-02107.html
, it appears that the product is just enriched flour without any barley malt or anything else. If that listing is correct, I would think that the San Antonio flour would be usable to feed your sourdough cultures. You might double check on this matter when you are next at the store where you would normally purchase it. BTW, I once used the San Antonio Tres Estrellas flour in Mexico to make pizza dough there, as I discussed in Replies 204 and 205 at http://www.pizzamaking.com/forum/index.php/topic,576.msg15668.html#msg15668
. If that flour indeed is only enriched flour, then that might help explain why I did not get good crust coloration. I think I would add diastatic malt to help solve that problem, as well as other things as I discussed in Reply 205 referenced above.
To the above, I would add than the last time I was in Mexico I brought back an empty flour bag of another Mexican flour, the San Blas brand, that I used to make pizza dough while I was in Mexico. I have shown a photo below of the front of the bag. The ingredients list reads as follows: Harina de trigo, aditivos (Acido ascorbico, enzimas, peroxido de benzollo), hierro, zinc, niacina (Vitamina B1, riboflavina (Vitamin B2,y acido folico
. I ran the Spanish text through the Google translator and got the following: Wheat flour, additives (ascorbic acid, enzymes, benzollo peroxide), iron, zinc, niacin (Vitamin B1, Riboflavin (Vitamin B2, and folic acid.
The only possible offending ingredient that I can see in that list is the benzoil peroxide.
I also tried another Mexican flour to make pizza dough during my last trip to Mexico, but the dough I made was frozen for future use. I was later told that that the dough was even better than the one made with the San Blas flour. I will have to try to see if I can get the name of that flour and the ingredients list for the flour. It was purchased in a small village mini-store as are very common in Mexico, as you know since you are in Bucerias.
Don, the bottom line on this matter seems to be that the Mexican flours you have been using are not bromated but may contain other things that are not the best to use to feed your sourdough cultures.