How long can you retard a sourdough during bulk ferment?

Hmmmmm, interesting question. If you retard your yeast breads for that long with no ill effects then obviously your fridge is cold enough to stop yest activity (fermentation), so that's okay. I have left my sourdough in the fridge for up to 18 hours with no problem (bulk ferment, not proofing; I always have a problem with overproofing at that stage), and my starter lives in the fridge for weeks without any apparent ill effects.

Maybe you could make some dough and form little rolls, then leave each one in the fridge for different amounts of time (leave one for 12 hours, one for 24, one for 48, etc) and see the difference in the finished bread.

You would have to do a search (I'm too lazy today to do it for you) but the sourdough experiment has been done and reported on this website.  Maybe the longest time was 36 hours (maybe longer, I cannot remember) and there was little difference in flavor IIRC.  I mix my sourdough first thing in the morning and it goes into the fridge about three hours later after several stretch and folds.  Bread is baked the next morning so that the total time of cold bulk fermentation is 20-21 hours.  I don't see any point in a longer bulk fermentation as I want to fit things into a certain schedule.

in the morning, make the dough before going to bed, let rise on counter over night, so about 6 to 7 hours later I shape the bread and leave it on the counter for an hour and then in the fridge till the next morning and bake it about 1/2 hour after taking out of the fridge (basically the time it takes to heat the oven).  On one occasion it stayed in the fridge for 48 hours and I was scared that it would not brown because all the sugars would have been consumed, if anything those loaves browned nicer.

Gerhard 

I've done it over 2 days or about 36-40 hours.  I wouldn't go longer with the same amount of starter.

the pervcent of pre-fermented flour in the dough and how long it was bulk fermented onthe counter after mixing.  So the answer is it depends.  At 12% prefermented flour and 3 hours after mixing on the counter I can get 24 hours but have done up to 36 hours with less levain  It has also over-proofed at 18 hours with 20% prefermented flour.

In bread baking,  everything is relative...

The great Socrates of TFL has spoken. "In bread baking, everything is relative . . . "

For how long you can bulk ferment sourdough, so much depends on so much else. Percentage of levain is a huge factor . . . using less levain means you can push the bulk fermentation further, but too little levain and you won't get much fermentation at all, even at room temperature (I've had some trouble below 5% of flour weight). But other factors will weigh in as well : the base temperature [(temp. flour + temp. water + temp. ambiant) / 3] will influence fermentation rate (higher base temp, quicker fermentation, and vice versa) ; as will type of flour used and its freshness (whole wheat will go faster than white, ditto with rye).

If I use less than 20% levain, I can usually get away with 6-8 hours in the fridge for a bulk fermentation after 2 hours at room temperature, if I use semi-complete wheat flour (T80, here). However, if I add a good chunk of whole rye or whole einkorn, after about an hour of fermentation the fridge isn't going to help, since cooling down a big batch of dough takes too long and by the time the yeast have gone to sleep they've already done their work.

In summary, it's a complicated but very good question !

If you put the dough into the fridge just after mixing, if your fridge is 37F, example bulk fermentation times at different amounts of innoculation are:

15% starter (7.5% innoc): up to 163 hours (then shape, proof, and bake)

40% starter in mix (20% innoc): up to113 hours.

Those times are based on the published formulas for bacteria and yeast activity levels for a range of temperatures, and the activity levels of my white flour starter, which I measured a couple years ago.  I've tested the formulas, so I think it's right, although I'd still end the fermentation maybe 5% early, to be safe. 

The idea for me is to use the fridge (along with a small, cheap wine cooler with good temperature control) to control the time fermentation lasts so I can choose convenient times for mixing and baking.  It used to be I'd have to dedicate a day to the bread, now it's just an hour or two here and there I have to plan for.  The fact that stretch/fold becomes unnecessary when you extend fermentation past 8 or 10 hours makes it that much easier.

Example: I have time to mix now, so I do it and finish at 1:30pm.  If I want to bake tomorrow evening around 7, then I can put the dough in the fridge until tomorrow at 8 when I leave for work.  At that time I'll put it in the cooler at 65.  At 5pm tomorrow, I take it out shape, proof and bake.  In order to get those times just right, I only have to adjust the recipe so that the starter % is 24%.