The Fresh Loaf

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Definition of Sourdough

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KelleyAnn11's picture
KelleyAnn11

Definition of Sourdough

Hi all-

I was wondering if anyone could define sourdough for me. Does a bread qualify as a sourdough if it has a an overnight cold ferment (such as with Peter Reinhart's breads)? Or is it only a sourdough if it employs a maintained sourdough starter? Any help would be much appreciated. Thanks much.

fancypantalons's picture
fancypantalons

To qualify as a sourdough, the bread must contain a portion of wild yeast starter.  Otherwise it's just traditional, commercially leavened bread.  Long-period, cold fermentation is really tangental to the definition, as it's a technique used with both sourdough and commercially leavened breads, the purpose of which is to give bacterial and enzymatic activity time to work, in order to improve flavour depth and complexity (and in the case of sourdough, to enhance sourness).

Incidentally, I include in this definition breads that are leavened with a combination of a wild yeast starter and commercial yeast.  Not everyone is so opened minded, though. :)

KelleyAnn11's picture
KelleyAnn11

Ok, so a second question then...I was reading about how sourdough breads do not cause the same rapid rise in blood sugar levels as do commercially yeasted white breads. My understanding was that the fermented nature of the bread somehow interfered with this reaction. So, if the purpose of the long-period cold ferment is to increase enzymatic activity, would it stand to reason that these breads also might not cause the blood sugar reaction?

fancypantalons's picture
fancypantalons

Honestly, I have no idea.  In fact, I'm not even convinced the original supposition (that sourdough has less effect on blood sugar levels) is true, and I'd want to see evidence from a study or two before accepting that as fact.

In terms of enzymatic activity, I have no idea how that would affect blood sugar levels.  I can say that the activity of those enzymes, specifically alpha and beta amylases, is to break down long chain starch molecules into simpler sugars.  This gives yeast and bacteria food to feed on, and the result is greater flavour complexity (as both produce acids and other by-products which affect flavour), and often a sweeter loaf (I find long-fermented french bread is surprisingly sweet, despite there being no added sugar, a consequence of the long, cold fermentation).  In addition, there is some activity (which, I presume, is enzymatic in origin) which breaks down flour proteins into amino acids.  

The difference between sourdough and commercially leavened bread is the yeast and bacterial action that goes on in the bread.  Unlike commercial yeast (which is derived from brewers yeast), wild yeast cannot digest maltose.  As such, the yeast activity is significantly lower, while bacteria have a chance to work.  In the case of sourdough, in addition to yeast activity, the various sugars and amino acids in the dough are also ingested by lactobacillus, producing lactic and acidic acid as a by-product (among, I'm sure, other things).

But how any of this affects blood sugar levels following ingestion, I have no idea.  That is for properly constructed studies to decide.

Update:

Well, I found at least one reference:

http://findarticles.com/p/articles/mi_m0854/is_12_29/ai_n17215851

That article claims (though I didn't notice a supporting citation) that studies indicate that the acid content in the bread may reduce blood sugar response following ingestion.

If this is true, the answer to your question is simple:  long fermentation won't help you in the case of commercially leavened dough.  The effect is a consequence of acid content, and non-trivial amounts of lactic and acidic acids are only present in true sourdoughs (or sourdoughs that are spiked with commercial yeast).

PaddyL's picture
PaddyL

...since you can leave the sponge, or primary batter, on the counter overnight before mixing up your dough.  When the dough is mixed and left to rise a second time, it usually takes up to four hours or more to rise, depending on weather conditions and ingredients, so you're getting the long fermentation necessary for the chemical whatsits to happen.  I've been making white sourdough now for a few months, I'm diabetic, and the bread I've been eating is not shooting my blood sugar through the roof.  It's staying at normal levels.  I have heard of someone, also diabetic, who buys rolls made with a poolish, and they don't have the same dire effect that plain white rolls do either.

KelleyAnn11's picture
KelleyAnn11

Thank you for such thoughtful, complete answers. I am in awe of your understanding of the chemical reactions and I really appreciate the first hand response from someone who tests blood sugar regularly.

Kuret's picture
Kuret

The only study I have read is one wich does not specify the different breads eaten in the study, so there might as well be more factors to it.

The sourdough leavened bread might taste good enough without added sugars so it therfore has a less rapid effect on blood sugar. I know real french bread does not cointain added sugar but I believe that supermarket "french" often does.

This may also be the case with poolish bread. Although acids are quite commonly said to reduce the digestive activity, on what grounds I don´t know.

 

PaddyL's picture
PaddyL

...is that I read, I tried, and with me, it worked, even though I added some sweeteners, sugar or honey, to my sourdough breads.  I have eaten commercially-risen (dried yeast) white bread, very lean, no sugar, and my blood sugar responded accordingly; it went up pretty rapidly.  The sourdough white bread does not cause my blood sugar to spike at all, and I test myself at least a couple of times a day.  It may not work this way with all diabetics, but happily, with me, it does.  Sourdough is also thought to be good for other digestive problems like lactose intolerance.  The studies are ongoing and I'm sure we'll hear more about this as time passes.

jonesy's picture
jonesy

I am still struggling with a description of being "tangental to the definition" I thought for a mo' we were on to The Beatles old Indian Guru. My search was please define sourdough. Thanks Paddy L for the info. All clear now. Regards all you bakers

KelleyAnn11's picture
KelleyAnn11

I guess I'm basically just not clear about the enzymatic difference between a poolish bread and a true sourdough. Any thoughts?

fancypantalons's picture
fancypantalons

According to the abstract for this article:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WFP-4KXWJT3-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_...

The lower Ph of sourdough results in enhanced protease and amylase activity