After much trial and error and little success, I think I know why I've had so much difficulty in replicating the old-school San Francisco sourdough breads of yesteryear, made by Larraburu, Parisian, Colombo, etc.
Those breads were very, very sour, with a strong lactic-acid note. It is very difficult for the home baker to replicate the strong sourness of those breads. I've come close to the old-school flavor and aroma by way overproofing dough, but this overproofed dough is unworkable. It is nearly liquid in consistency and does not result in a viable risen loaf.
What we know about the old-school sourdough process is that a stiff sponge of about 50% hydration was maintained. This sponge was refreshed every eight hours (three times in a 24-hour period) and was kept refrigerated. I think this accounts for the strong sourness of the bread.
The bakeries of yesteryear were baking 24 hours per day, seven days per week. They could thus consume the sponge as quickly as it was refreshed. That is to say, sponge refreshment kept pace with the demand for sponge in the baking of bread. The home baker is likely not baking 24/7 and is likely unable to refresh a sponge every eight hours without generating a surplus of starter which might only be discarded.
I believe this is why the very sour, old-school sourdough is difficult for the home baker to replicate. The 24/7 baking regimen of the erstwhile bakeries and the requisite sponge refreshment schedule was the main contributing factor to the strong sourness of those breads.
When I was making it, it had a growth of kahm yeast at the beginning. With time I managed to get it under control and it went away. However, if left unfed (even in the fridge) for about a week the kahm yeast would be back. Then again, with some TLC and a few feeds it went away once again. However the resulting bread was very sour. Not nice at all! I think the flavour should come from the grain itself with the fermentation enhancing it. I've since made a new starter and it's far nicer. So if San Francisco breads were as sour as you describe then it's not something i'd be after.
That SFSD flavor certainly is elusive. I've occasionally tried experiments to vary parameters to produce a more sour loaf to no avail. I have produced sour rye loaves, but then rye doesn't break down the same way that wheat gluten does.
I'm still trying to find a way to reliably achieve that flavor with batch parameters instead of a cold proof (too small fridge). Most of the "extra-sour" SFSD recipes I see use that cold proof to increase sourness. We know that method wasn't used in the old Larraburu process.
We do know that the sponge was refrigerated between refreshments.
Still, what home baker is going to rebuild a sponge every 8 hours and consume all of the sponge they build?
doughooker,
If you're interested in a deep dive, Brod & Taylor provides a write-up of the process which can be found on their website at:
Part I — How to Make Sourdough More (or Less) Sour
https://brodandtaylor.com/blogs/recipes/make-sourdough-more-sour
Part II — How to Make Sourdough More (or Less) Sour
https://brodandtaylor.com/blogs/recipes/make-sourdough-more-or-less-sour-part-2
I've used the information and methodology to make some very sour sourdough bread.
Tony
I've tried the B&T instructions for making more sour bread and it didn't seem all that sour. I also tried Teresa Greenway's Northwest Sourdough method (bought the course) with the same result.
I've also explored the original Larraburu process as outlined by Kline and Sugihara and Galal, et al.; and a method using acid whey from a US patent. None so far have yielded the SFSD that tastes sour enough.
I'll keep trying, though!