Why does the quantity of yeast in a bread dough matter?

[Shalmanese]

The entire point of fermentation is to allow the yeast to grow right? Doesn't that mean a bread dough with half the amount of yeast mean that you just have to wait an extra doubling time to get the yeast back to the original level? Sure, the bread will rise slower but the end effect should be the same right? Or am I misunderstanding something about bread science?

[jmolinari]

The flavor of bread is developed over time through enzymatic action, breaking down of starches to sugar etc.

Using less yeast allows for longer fermentation without over-rising your bread.

That's why fast risen breads are generally not as tasty as slow, refrigerated rises. It's cheaper (saves times) but the flavor suffers to use more yeast.

[Panaderia Canadiense]

Also, in high-altitude baking more yeast is strictly necessary to provide a sustained rise in the bread, long or slow proofing times notwithstanding. If you try low-yeast breads here, even if you give them overnight to ferment, they're still going to turn out flat and disappointing, even though they may be tasty. This is because of the way the final product behaves at low atmospheric pressure.

I had to completely reinvent many of my recipes for 10,000 feet - the low-yeast ones simply wouldn't come out.

[weinoo]

And don't richer doughs require more yeast to help them rise?

[Panaderia Canadiense]

They do, because fats can encapsulate the yeast cells, preventing them from growing. More yeast in those cases ensures there's enough non-encapsulated yeastie beasties to effectively rise the bread.

[jmolinari]

No one likes being encapsulated, especially yeasties!

[Panaderia Canadiense]

It's also the reason that fats are often added to very rich breads after the first rising.

[emannths]

I'm not sure how this manifests itself in baking, but in brewing, the amount of yeast added to the wort is a key factor in the flavors created by the yeast. Generally, if few yeast are added, they tend to create stronger flavors (often unwanted in beer). Perhaps the reason for adding small doses of yeast to leavened breads is to get the little buggers to pump out more yeasty flavor.

The flavor of bread is developed over time through enzymatic action, breaking down of starches to sugar etc. Using less yeast allows for longer fermentation without over-rising your bread.

I'm not sure this is right. I would think that the amount of enzymatic action would be a product of both time and number of cells, i.e., each cell has the same amount of enzymatic action per unit time, so you could either double the amount of time or double the number of cells to get the same effect. Not true?

[jmolinari]

I'm not sure how this manifests itself in baking, but in brewing, the amount of yeast added to the wort is a key factor in the flavors created by the yeast. Generally, if few yeast are added, they tend to create stronger flavors (often unwanted in beer). Perhaps the reason for adding small doses of yeast to leavened breads is to get the little buggers to pump out more yeasty flavor.

The flavor of bread is developed over time through enzymatic action, breaking down of starches to sugar etc. Using less yeast allows for longer fermentation without over-rising your bread.

I'm not sure this is right. I would think that the amount of enzymatic action would be a product of both time and number of cells, i.e., each cell has the same amount of enzymatic action per unit time, so you could either double the amount of time or double the number of cells to get the same effect. Not true?

The action of yeast and enzymes, i believe, are 2 different things. Then again, i could be completely wrong and saying something moronic.

[scott123]

The action of yeast and enzymes, i believe, are 2 different things. Then again, i could be completely wrong and saying something moronic.

You're mostly right Because yeast produce enzymes of their own, yeast activity and enzyme activity are not entirely separate processes. Because the enzymes in malted barley are far more numerous and impactful, though, the enzyme activity from the yeast is relatively inconsequential, allowing one to look at yeast activity and enzyme activity as fairly independent processes.

Now, bear in mind, this is for traditionally malted flour. Switch to an unmalted flour (as well as, perhaps, a higher falling value/less germinated/lower enzyme flour) and the enzymes generated by the yeast become much larger players.