That doesn't make sense to me, unless you mean the 'normal' instant yeasts supermarkets sell only work with wheat? If yeast from natural exposure would work then surely one of the plethora commercial yeasts (or marketed for homebrew) would do the trick?

You can use commercial yeast, but it will never be as light as with sourdough fermentation, but very dense and “soggy”.

There are more factors at play here but the tldr is that, other than wheat, rye flour contains a very high level of amylase, an enzyme that breaks starches into sugars. Amylase prevents bread from rising, and rye contains so much of it that it stays active even with the high temperatures of baking. Add that to the fact that rye has very little gluten to hold up the structure of the bread…

That‘s where sourdough comes into play. The acids produced during a slow fermentation slow down the reaction of amylase, giving you a lighter bread. For a good rye bread, I ferment for over 24h in three steps.

Is that a lot? I ferment my regular wheat bread for over 24h. (Started some off this morning as it happens, will likely bake it tomorrow evening.)

Any self-reapecting pizzeria will cold ferment for three days before attempting to make pizzas with it.

I think/thought this thread had devolved into 'regular' loaf bread - indeed my pizza dough spends at least a day in the fridge after a slightly shorter time 'bulk' outside.

Interesting you say that though, because I find three days about the limit, starts to really over-ferment, becoming really 'pockety', even at refrigeration temperatures. I suppose if I did it all in there as you imply, no fermentation time at room temp. at all, that might be better?

How much salt are you adding? How cold is your fridge?

How active is your sourdough starter? Commercial yeast by contrast tends to be very active, so timings are shorter.

Correct timing depends a lot on temperature and how much salt you add to your dough.

Sure, I was just questioning the implication that 24h 'because rye' was a lot really. (Or if that was the the implication.)

No, I just meant to say sourdough fermentation is slower than a quick rise enabled by commercial yeast. Though I do ferment rye breads longer than wheat, and with a rye bread, you would also usually sour more of the bread, like up to 50% of total flour amount.

That said, I think they cultivate newer rye varieties to be less rich with enzymes. I presume that is to meet the requirements of industrial baking.

The yeast works just fine in rye.

(Though you shouldn't use that kind of yeast for breadmaking, if you want it to taste good.. At least get some fresh yeast. (Which not quite coincidentally is also the 'normal' kind of yeast in eg Germany.) Better yet, make a rye sourdough starter.)

The problem is that rye doesn't have enough gluten. So you need to get the structure of your bread from the starches, and they only do the Right Thing when it's sour enough. See https://news.ycombinator.com/item?id=36504484 for a slightly more in-depth description.

Aha! So that’s why a true rye bread tastes so good!

Rye also has different trace minerals than eg wheat or barley. That's part of why rye ale tastes different from wheat beer tastes different from barley beer.