After accidentally stretch-and-folding a loaf into near soup, I asked here if it was possible I had overkneaded. Instead a new term entered my vocabulary: thiols! However, I've found it near impossible to find out much more about these mysterious and oft-titled "pesky" by-products of unwelcome bacteria. Google yields very little, and what I can deduce from TFL is incomplete and added to with other mysterious terms I don't understand yet. It's possible that my case is something completely different, or that thiols aren't what's causing these issues at all. I thought I would document my experience, as a newbie, for future reference.
The main agreed effect of thiol is said to be the starter and dough turning very sticky and eventually liquefying, at some point after adding starter, and not at all if commercial yeast was added (ie not really a sourdough). The wonderful Debra Wink's solution for thiol in starter is an intense feeding regime, resulting in a sudden fix about 10 days later. I recognise that a similar effect and solution present themselves in an overly acidic starter, but rather than "washing out", as for too much acid, for thiols this solution is intended for rapidly re-establishing a wonky starter. In other words, outpopulating the unwelcome beasties with desirable ones. The reason is that the starter is not as established as supposed due to destabilising factors (changing hydration, refrigeration, changing flour, etc). Well, I don't run a bakery, so why not try?
Let me describe my soupy loaf first. It used about a third levain from a starter revived from the fridge a fortnight ago.
It wasn't soup when I started being concerned - it had achieved an approximate windowpane, but I wanted more, and I didn't think I'd given it that much kneading. After one more stretch and fold I became concerned as the windowpane started breaking, and sticking to other things rather than itself like a glue or paste rather than a dough ball, a behaviour I vaguely associate with overstretched gluten.
I should have dumped it straight into the pan at that point, but I ignored my gut and shaped it twice. Bad idea. By that point it had liquefied further, spreading over the countertop despite being a 65%ish hydration. I dipped my hands in flour and heaved it quickly into the pan, which it filled.
During its rise, what gluten there was provided little to no resistance, so I could see all the bubbles as they formed and then broke. It also smelled really unnatural, like new, cheap plastic. Very unappetising. I've never smelled food/to-be-food that smelled like that. Eventually it overproofed, though this was difficult to tell since the surface was full of craters from the start. Once baked it had lost that plastic smell, replaced by a very complex, still unappetising smell - honestly, it reminded me of old urine. We composted that one immediately.
On being enlightened by Debra's feeding regime, I proceeded to discard a large amount of the starter. And then my frugal experimental brain said, why not bake something with it...
The second (mini) loaf behaved similarly in terms of gluten development. It took barely combining the water, flour, starter and salt properly to achieve what appeared to be a smooth gluten network, so I didn't even attempt stretch and folds. I bench rested it, minimally shaped it, then put it in a pot to rise. This was much more successful with no weird smells, apart from craters in the surface and somewhat underproofing it. It certainly behaved and rose like a 65%ish hydration dough and not an 80%ish one!
Under the same feeding regime, by the next day (today) I had enough starter to make another mini loaf. This would be the third one with a (possibly) thiol-infused starter. Once again very fast gluten development coupled with a lot of bench rest and minimal shaping. It was starting to stick to the floured scraper a little and you may be sure that I got it into the pot as fast as I could at that point. This time, I tried not to get a particularly stretched outer gluten layer in the shaping, and covered it with a teatowel to allow the surface to dry rather than get craters. To my surprise the oven produced a very acceptable, well-risen loaf with no hint of gluten problems.
I'm now eating a deliciously crispy-crusted, tender-crumbed, thickly-buttered thick slice of thiol bread and pondering these pesky mysterious unwanted by-products. Maybe thiols just make an AP flour loaf behave more like a rye or low-gluten wheat flour in mixing and kneading? Or maybe it's just me, not thiols at all - maybe I've been kneading sourdough wrong, and that first loaf was just catching the starter at the wrong time. But what was that plastic smell? Not to mention the old urine. Or maybe the thiols really were the reason for all those early sourdough flops after all. My memory is vague at the best of times, and in pregnancy it's a downright sieve.
I'd better finish off this last slice. Gotta go feed the starter.