Favorable temps for Acetic and also Lactic bacteria?

It's only Lactic Acid Bacteria (LAB)

Sourdough starters that are maintained with continuous refreshments are dominated by one or more heterofermentative LAB. These bacteria metabolise sugars to primarily lactic acid but will produce a number of other metabolites such as CO2, acetic acid and ethanol.

Use the search box for "Detmolder" and u will find many posts.  Google it too...

Cheers

Lactic acid (mainly - the base sour) but can be prompted to produce acetic acid (the 'tang') Great SD bread has both sour and tang.  Generally speaking, high hydration and temperatures make for lactic acid and low temperatures combined with low hydration will make the LAB produce acetic acid and bran will allow the LAB to produce acid at lower pH's than normal.  This is the thought behind and basis of, bran levains and whole grain starters, the NMNF long retarded / low hydration starter, high hydration room temp and higher levains, retarding built levains for a day or two, retarding the lower hydration dough for final proofing and doing bench work at higher temperatures or a high temperature final proof.

All promote more acid production and some promote more acetic acid production.  

at the same time.  I think they usually produce one or the other.  If they could be made to produce both at the same time that would be the perfect scenario to make SD bread.  The supposed famous Larraburu process for their sour bread was a lower hydration and very high final proofing temp at 91- 92 F that favors LAB reproduction rates over yeast at 13 to 1.  The yeast favorite temperature is 84 F.  So at 92 F the yeast is being restricted like it was 68 F.  So proofing took the time like it was 68F, fairly slow, but the LAB made lactic acid like crazy making for a very sour bread that San Franciscans at the time loved the best.

I don't know if Larraburu used baskets to proof their thousands of loaves they baked every day or not.  I have always assumed not since their hydration was only 64% or so,  and that would keep the loaves from spreading too much as they proofed and allow for free form proofing which would be much easier on the bakers.  LAb and yeast both love the wet the best though but hydration, like all baking things, is relative.  Once you get wet enough it really doesn''t make that much difference on how well LAB and yeast do their work.

Neither yeast or LAB like the cold (36 F) very much though.  Both slow down their metabolic and reproductive rates to a near standstill but LAB do out reproduce yeast 3 to 1 at that temperature but it takes a very long time for the LAB to build up larger LAB to yeast ratio at that temperature - weeks and weeks and weeks.  I start to notice a difference with my NMNF starter at 16 weeks in the fridge.  But, if you can get a starter to have a higher LAB to yeast ratio to begin with, the higher LAB will continue to permeate the levain and dough, since LAB out reproduce yeast at every temperature, so it will produce a more sour bread because there is more LAB than yeast than normal SD bread processes.

Low hydration say 66% and low temperature, under 40 F. supposedly help the LAB make acetic acid over it's preferred lactic acid production at other higher temperature and higher hydration.  But, keeping the NMNF starter at 66% hydration for 24 weeks in the fridge, isn't because I want it to make lactic acid - I just want to increase the LAB to yeast ratio of the starter and that takes a very long time at 36-38 F.  When you only use 10g of starter to make a loaf of bread you won't notice any extra acetic acid in the tiny 10 g.

To get the acetic acid tang in SD bread, people retard their much larger levain  builds at low hydration and do the bulk ferment or final proofing of the dough for a day or two or even several days - to try to get the tnf=g in their bread,  Dough is usually at some hydration in the high 60's or low to medium 70's which I consider that low enough hydration to promote acetic acid production.  The Detmolder process where the levain is stiffened up and put into the fridge for stage 2 is a way of trying to get the LAB in the levain to make acetic acid.

Hope this helps

I have also always thought that the idea that gluten and structure of the bread was broken down by protease action in white bread was a total and complete urban myth.  Under normal bread production processes and times for fermentation and proofing, white flour has too little protease to cause the destruction of the gluten and structure of the bread. That isn't to say if you leave the bread on the counter for 3 days to bulk ferment it is going to be fine but that isn't a normal process for making bread.  You also can't leave the dough on the counter for 3 days to final proof either at normal room temperature.  Even if the bread over proofs a bit too much you can always reshape it and let it proof again - no problem.  The worse that can happen is that the crumb is a bit more dense, it might be a bit more sour or it might not brown as well.