Minimum amount of yeast

And even instant yeast is only one form of a variety of yeast.  If you are aware that there is wild yeast in the flour also, I guess the minimum amount would be "none."  There are recipes where no yeast is added and the flour ferments with the liquid that has been added to it.   The problem that may arrise is: will the dough strength hold up long enough for all the yeast replication that is needed to raise the dough using yeast?

The reason different recipes call for different amounts of instant yeast even with the same amount of flour, is to vary and control the fermenting process. That is what flavor is all about.

Yeast reproduce by budding and they double their population every hour to 2 hours under ideal conditions.  Yeast can also run out of available food and they produce products that when a saturation level is reached, slow down or stop the yeast from budding.

Lets back up a little bit.  It might help to think of the whole dough and fermentation as a negative process with positive results.  From the time ripe grain or flour gets wet it purpose is to feed a new plant as it degenerates and falls apart eventually back to basic elements.  Fermentation is in reality the breaking down of the flour.  It goes thru different stages of decomposition and we take advantage of this process trying to control it and  make usable food.  

There are also enzymes in the flour (some are added to instant yeast) that also react as well.  Various gluten levels can lengthen dough strength.  Factors vary from flour to flour and in different quantities and these even vary from season to season, year to year.  All have influence on the fermenting process and our ability to trap the by-products of fermentation, gas, acid, aromas, etc. to make bread.  It is a balancing act.  

It is also important not to let the process advance too far too fast out of our control.  We control the factors: moisture, temperature, yeast and each ingredient and expect certain results.  All the factors have parameters of too much or not enough with losses or gains that affect other factors both positively and negatively.  The mind boggles!  A good recipe has these factors all in consideration and by following it, you should come out with decent bread. Many are pretty flexible and so "tweaking" a recipe with small changes is easily done.

I like to reduce the yeast when I want a longer fermenting time than the recipe.  I start by reducing in half first and seeing what happens, then add more or less.  If the recipe doesn't have a total wet time of at least 6 hours, I reduce the yeast.  That is my rule of thumb.

Mini

Zdenka,

I saw your post and was going to answer but Mini just covered the subject so superbly that there is but little left to be said.

Jeff

As to the health-related effects of baking with wild yeast (aka sourdough) or using longer fermentation times with regular yeast, see this 2007 thread: Healthy Sourdough

FreshLoaf user Andy (is that the same person as AndyM in this thread?) does a really good job of explaining things. In summary:

• additional fermentation does a better job of releasing enzymes and pre-digesting the dough so that the humans can process more of the nutrients from the bread
• sourdough contains more variety of organisms which do a better job of the above, but commercial-yeasted preferments still help
• there may be benefits to the fact that some of the lactic acid bacteria in sourdough are actually the same species as some healthy intestinal flora in humans (so-called probiotics). However this is hard to say for sure because the organisms are killed in the oven, so it would only be true if something they did to the dough, made it more beneficial to those organisms once the bread makes it to your intestines.

@zdenka, regarding using commercial yeast and sourdough together: In Whole Grain Breads Peter Reinhart includes a lot of hybrid recipes that use both a sourdough preferment and commerical yeast. The commercial yeast is added at the end to speed up the final bulk ferment & proof*. So you can definitely use both in the same recipe, I think it's a matter of understanding what they're doing.

*he says he needs to speed it up because of how he uses whole-grain soakers, and once the soaker is combined with the preferment the dough can break down quickly due to the high amount of enzymes in the soaker.

I think it may be true that over a longer period of time, the acid in sourdough may kill of the commercial yeast, I've heard that before too.

Mike

Saccharomyces cerevisiae - if you use less of it in a recipe, it will increase during the longer fermentation anyway... or not?

Yes it will increase.

is it correct to say that using more commercial yeast is less healthy?

No it is not correct to blankly say that.  There is much discussion and debate, not only about the yeast itself (allergy or intollerance) but about the short fermenting times that can be achieved by using it.  Wild yeast have a symbiosis with bacteria found living with wild yeasts cultures.  So one cannot compare them without including a debate whether these bacteria make a bread more healthy.

It is possible to use commercial yeast and prolong the fermenting time.  Seems to go against trends and be a healthy option.  Truly more studies need to be done.  And the question... less healthy than what?  Using more than the recipe stipulates?  Yeast gives a kick to the fermenting process; speeds it along.  There are some who eat denatured yeast regularly as a supplement.  Commercial yeast also has a more neutral flavor and can easily be used in sweetened or unsweetened doughs.  It certainly has its place as a tool.  A speedy wild yeast could also present debate with fermenting times.

what happens when commercial and wild yeast are in the dough together? I have read that the commercial yeast would not survive the acidity created by the sourdough.

When they are thrown together, how much of each?  Ok, the commercial yeast goes after its food, the wild one too.  The commercial yeast is fast to produce gas to raise the dough, you have to decide to bake it when it's ready or risk loosing total dough structure.  The wild yeast did not have the chance to work with their bacteria, they need more time to raise the acid levels too.  So I ask you, did the commercial yeast bow to the sourdough?  Hardly.   At most the wild starter added a little flavor. Now one could make the dough with the sourdough first, and later add the commercial yeast for a fast final lift.  This is often the case to guarantee rise in very sour doughs or to make a less sour sourdough cutting the long fermentation short.  If the sourdough would kill the commercial yeast on contact, then there would be no reason to use commercial yeast in this way.

However; if you are maintaining a starter and both are together, eventually the rising acid levels and long feeding cycles make it harder for the commercial yeast to survive, it will eventually be overpowered by sheer numbers of the wild yeast (could be more than one type) and their acid producing groopie bacteria.   The acid at high concentrations will slow all the yeasts from budding and I suspect a little more complicated than just that but the commercial ones are less flexible when it comes to survival.   This could take weeks but the wild ones will come thru.

Zdenka,

While I would not call commercially yeasted bread "unhealthy", I do eat sourdough bread almost exclusively because of health.  A little yeasted bread can make for an uncomfortably full stomach whereas a lot of sourdough does not have that effect.

When comparing yeast vs. sourdough I would say that sourdough is a much healthier choice but that does not make yeast un-healthy...although I do have my doubts about the health aspects of yeasted bread.

Sourdough is essentially a fermented food and like yogurt or sauerkraut, and these are foods that are very good for the body,

Jeff