April 13, 2012 - 3:16pm
Two sourdough levains. Why is one more sour?
Two sourdough levains.
- 1000 g flour, 1000 g water, 10 g starter, 12 hours fermentation, 76 F.
- 1000 g flour, 700 g water, 10 g starter, 12 hours fermentation, 76 F.
Why is 2. significantly more sour than 1., all other things being equal?
Isn't it temperature that affects sour, with colder temperatures encouraging (the lactobacilli produce) greater sour?
If so, why the difference in sour with these two with only a difference in hydration?
What am I missing?
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You have fallen under a common misconception that lactobacillus prefer cold temps or produce more acid at colder temps. Not the case. Both yeast and lactobacillus work slower at colder temps.
Time, temperature, hydration and flour type all have an influence.
Dough 2 with the lower hydration will work more slowly and consequently develop more acetic acid than dough 1.
EDIT: Please read Debra Wink's Post on the subject.
Your results conflict with Debra Wink's post at this link:
http://www.thefreshloaf.com/node/10856/
But I don't understand it either (why hydration makes a difference). It is an area badly in need of some controlled experiments.
Your definition of sour is based on taste which is generally thought to measure total titratable acid (TTA) and not pH, so the experiment is not simple since it requires a titration to measure TTA with some level of accuracy and repeatability.
If somebody wants to start defining a series of experiments I would be happy to participate.
Doc
Remember there is sour in the dough and sour in the bread.
In the dough, Acetic acid, even in small quantities is much more sour tasting than lactic.
Being that acetic acid is more volatile than lactic, in the cooked bread acetic acid contributes to flavour but doesn't provide a sour taste (or perhaps not to a noticeable degree).
With lower activity, acetic acid has more of a chance to build up.
Being that I keep an Italian style sourdough it forces me to understand these acids more clearly. I recognise the difference in taste of acetic and lactic.
As for Hydration, It tends to be commonly accepted that everything happens faster in a wetter dough. Given that with 0% hydration there is no activity it would make sense that wetter equals more activity.
I don't know the details but water is used to flush acidity to make working more favourable. Increased acidity hinders growth and activity - free water dilutes the acidity.
I plan to write an article on my findings at some point but It could be a while before I get round to it. I'm no chemist or biologist.
I'd be happy to participate in some experiments too. I have the abilty to measure pH (universal indicator) and maintain control of warm temperatures.
Michael
but check pH, temp every hour and temps before and after mixing.
I would like to know the temps of the flour and water.
In the posted experiment, if the water was colder than the flour then less water would mean that the 70% hydration starter was warmer than the 100% one which could speed up fermentation in #2.