I have been wondering about some information that I have always read concerning sourdough. Using wild yeast is suppose to be healthy for you. I am wondering how this is, if they die when you bake them?
My understanding is that it is not the yeast per se that accounts for the health benefits of sourdough bread. Rather, it is the acidity, contributed by the lactic acid bacteria in the sourdough culture, that has effects on the proteins in the dough as it is fermenting and leads to:
- A lower glycemic index (sourdough bread raises the blood sugar more slowly than regular bread)
- Better absorption of minerals in whole grain bread (whole grains are high in phytic acid, which impedes mineral absorption; sourdough breaks down the phytic acid)
- There is also some evidence to suggest that some people with celiac disease (gluten intolerance) can tolerate some sourdough breads
Susan is right in all points.
Regular whole wheat flour has phytic acid which prevents absorption of the phosphorus, calcium, zinc, magnesium and iron in the grain.
Fermentation with regular yeast, removes some phytate, allowing for some mineral absorption. However even yeast doesn't do a good enoughjob. A study conducted in Denmark shows that regular consumption of yeasted whole wheat bread lead to a lowering of iron levels in women over long term consumption.
Sourdough does a much more thorough job, mainly because bacteria and yeast digest different materials in the grain. So in a sense twice as much is digested as with just yeast. Studies show sourdough removes 62% of phytate, while yeast 38%. And unlike yeasted breads, animal studies show sourdough actually increases iron in the blood. And all minerals are mostly absorbed from the grain.
Mineral absorption is by far the highest in sourdough. There are many benefits to this. Better growth for children, life extension. Disease prevention.
Naturally leavened bread contains lactobacilus, which helps generate the intestinal flora essiantial for poper digestion and elimination.
From Healing w/ whole foods by Paul Pitchford
the lactic acid from the lactobacillus that remains in the bread after baking does support healthy bacterial colonies once it gets into your body.
Thanks for the information. I know that soaking the grains overnights also with the phytic acid as well. That's why I was so glad to finally understand what a sponge is.
How about yeasted doughs made with a preferment or retarded for a day or a few days? Would these be any closer to sourdough than direct method yeasted doughs from a nutritional standpoint?
Yes. You are correct. There have been studies done with long term fermentation of various materials using regular yeast only.
Regular yeast is used to ferment all kinds of grains and plant material to produce alcohol. So they've done a lot of research into this.
For example, they found the optimum fermentation time for using yeast to make alcohol out of sunflower stalks was 24 hours at 30 degrees celcius.
Also interesting research done on yeast fermentation of wheat bran. They make a immune system boosting cancer drug with this in Europe. It's called Avemar. I've seen their patent. In it they reveal that the optimum fermentation time to extract the components used in their drug is 24 hours.
You can see this yourself, if you leave yeast and wheat out to ferment for a day. The fermentation continues throughout this time, releasing more wheat components from the flour.
So yes, there is definitely less phytic acid, and more mineral bioavailability. The bread is also more thoroughly pre-digested so will be easier on the digestive tract.
That's good to know, Andy. Erratic baking schedules would be much simpler if a sourdough culture didn't have to be maintained.
When comparing a long fermentated bread made with commercial yeast to a sourdough risen bread, how much effect does lack of lactobicillus have?
Sorry to get back to you so late. I haven't checked this thread in a while.
Have you ever overfermented sourdough? The dough gets weak, and rips apart really easily.
Yeasted dough takes a lot longer to decompose like this.
In sourdough there are a lot more species of microorganisms at work. There are often several types of natural yeast, and bacteria in the ferment. Each of them will ferment different parts of the grain more effectively than others.
So they break down different parts of the grain, making it super easy to digest.
That's why phytic acid which binds the phosphorus and other minerals in the grain gets deactivated so well with sourdough.
With regular yeast what happens with prolonged fermentation. Enzymes are naturally present in the grains. As well, the yeast itself produces enzymes. With the prolonged fermentation the enzymes are given the chance to break apart more complex carbohydrates, into simpler sugars which the yeast can digest.
The yeast cannot digest many types of complex carbs. Enzymes however can do break them down into simpler sugars. As a result the bread tastes sweeter, and the yeast is also able to break down more components of the bread.
However, it can't do this as much as sourdough. Since the lactobacillus are able to ferment different parts of the grain. This results in a much more thorough predigestion of the grain. Which means more mineral bioavailability, as well as other grain nutrients.
For example, Lactobacilus are able to break down the gliadin in the gluten protein. This is the part of gluten that gluten sensitive individuals react to. The lactobacillus break most of this down within about 4 hours. So celiac people can eat sourdough bread.
Yeast cannot do this. Even with long fermentation.
There are other benefits to the sourdough as mentioned before, regarding the glycemic index and control of blood sugar.
Andy, I appreciate all the information and clear explanation! I certainly don't mind the timeframe.
I have some friends with gluten sensitivities, though they haven't been diagnosed with celiac disease. I'll suggest they give sourdough bread a trial.
I read somewhere that regular yeast resembles cancer cells and also that regular yeast promotes yeast imbalances. Made me want to try sourdough because of that.
All yeast and lactobacilli in your starters are quite dead by the time you remove the loaf from the oven. If you're worried about handling dough, S. cerevisiae isn't much of a human pathogen unless you're totally immunocompromised, in which case you probably have bigger worries than baker's yeast.
Lysine is always the limiting amino acid in grain, but fermentation can multiply the amount of lysine. In wheat, you can triple or quadruple the amount of lysine, making bread a complete protein source!