Just some food for thought. I ran an experiment comparing the pH of
two samples of the same starter refreshed with different flours. Both
samples consisted of 10g of starter + 50g water + 50g flour. Both ran
at the same temperature (75°F to 78°F). One was made with fresh
ground whole wheat flour, the other was made with enriched, bleached
high gluten white flour. I think this demonstrates the phenomena of
whole grain flour buffering the starter and allowing the accumulation
of more total acid before the LAB growth shuts down at a pH below 4.0.
The most interesting result is the increase in pH during the first
hour. Anybody care to speculate on why this happens?

Look here for data:
http://picasaweb.google.com/DocDough/StarterPH/photo?authkey=W5xf8wUEzog#5217143234399849442"><im gsrc="http://lh5.ggpht.com/DocDough/SGcEIUy8S-I/AAAAAAAABEI/OoT2ArgoJQs/s144/Starter%20pH.jpg

Doc

On Sat, 28 Jun 2008 21:06:17 -0700 (PDT), Doc >
wrote:

>Just some food for thought. I ran an experiment comparing the pH of
>two samples of the same starter refreshed with different flours. Both
>samples consisted of 10g of starter + 50g water + 50g flour. Both ran
>at the same temperature (75°F to 78°F). One was made with fresh
>ground whole wheat flour, the other was made with enriched, bleached
>high gluten white flour. I think this demonstrates the phenomena of
>whole grain flour buffering the starter and allowing the accumulation
>of more total acid before the LAB growth shuts down at a pH below 4.0.
>The most interesting result is the increase in pH during the first
>hour. Anybody care to speculate on why this happens?
>
>Look here for data:
>http://picasaweb.google.com/DocDough/StarterPH/photo?authkey=W5xf8wUEzog#5217143234399849442"><im gsrc="http://lh5.ggpht.com/DocDough/SGcEIUy8S-I/AAAAAAAABEI/OoT2ArgoJQs/s144/Starter%20pH.jpg
>
>Doc

Hi Doc,

I don't mean to sound like a smart-a-s here but this is about the same
thing as saying "These two loaves of bread were made with different
ingredients yet they taste different."

What would be a surprise is if the starting and ending pH of the two
samples were the same.

Jack

I'd say, this is a potential measuring error asking for attention.

How often did you do the test or do you have some soap left in the
container which dissolves after a while?

What is the pH of the flours you use? That would be your baseline and
when you add some acid with the starters, it would go down.
That would be an interesting number to see the effect of 10 % of starter.

One effect may be happening. If you grow one starter on a particular
flour and then on another flour, there may be a higher time of
"retooling" used by the critters to adjust to the new goodies.


I was measuring SD pH's until it got too boring and never saw anything
like it - pH increasing after starter was mixed.

Sam

Doc wrote:
> Just some food for thought. I ran an experiment comparing the pH of
> two samples of the same starter refreshed with different flours. Both
> samples consisted of 10g of starter + 50g water + 50g flour. Both ran
> at the same temperature (75°F to 78°F). One was made with fresh
> ground whole wheat flour, the other was made with enriched, bleached
> high gluten white flour. I think this demonstrates the phenomena of
> whole grain flour buffering the starter and allowing the accumulation
> of more total acid before the LAB growth shuts down at a pH below 4.0.
> The most interesting result is the increase in pH during the first
> hour. Anybody care to speculate on why this happens?
>
> Look here for data:
> http://picasaweb.google.com/DocDough/StarterPH/photo?authkey=W5xf8wUEzog#5217143234399849442"><im gsrc="http://lh5.ggpht.com/DocDough/SGcEIUy8S-I/AAAAAAAABEI/OoT2ArgoJQs/s144/Starter%20pH.jpg
>
> Doc
>
> _______________________________________________
> Rec.food.sourdough mailing list
>
> http://www.mountainbitwarrior.com/ma...food.sourdough
>
>

On Jun 29, 3:46 pm, Sam > wrote:
> What is the pH of the flours you use? That would be your baseline and
> when you add some acid with the starters, it would go down.
> That would be an interesting number to see the effect of 10 % of starter.

The white flour when mixed without any starter at 100% hydration
yields a pH of 5.91, but this is a point measurement and I did not let
it sit and repeat it for the same batch over time. I will do that
next weekend and we will see what it does.

Each data point is the minimum of at least three measurements. The
ISFET sensor was calibrated (2-point) at the beginning and at the end
of the series (and just prior to the second calibration it was reading
4.08 in the 4.01 buffer so it had not drifted too far).
I agree that it looks like a small amount of something (a buffer of
some kind) is slowly dissolving.
I suppose it could be something leaching out of the bran as it
hydrates, but the phenomena is not limited to whole wheat flour.

I have two other time series on larger batch sizes (but with longer
intervals between data points) that show the same behavior, an
increase in pH over the first hour, then a monotonic decrease.
Of the four data sets, two were collected from samples in glass jars
and two from samples in stainless steel bowls.
Today I did a batch that started with starter at pH 4.1; added water
and dispersed the starter - pH stayed at 4.1; added salt and high
gluten white flour and mixed - pH 5.07 at end of mix; an hour later
the pH was 5.82; after another hour 4.55.

Doc

On Jun 29, 3:46 pm, Sam > wrote:
> I'd say, this is a potential measuring error asking for attention.

Yes, after rerunning the experiment with closer attention, it was
probably a measurement error associated with a small area ISFET in a
recess where it is easy to retain a small air bubble when the sample
is viscous.
When I went to 200% hydration sample, the problem became easier to
avoid, but the sensor is still very sensitive.
Look he
http://picasaweb.google.com/DocDough...ighGlutenWhite
for a new data set.

The high gluten white starter was mixed at 100% hydration while the
whole wheat was 200%, and I think that both of the excursions from
smooth curves could be reflections of the "bubble" phenomenon. For
each data point, two calibration samples were read (at pH 4.01 and
7.00) after measuring both starter samples. These calibration samples
were used to remove sensor bias drift (all adjustments were in the
range of .02 to .04).

It is still possible that there is a small pH increase after the
initial mixing of starter, water, and flour, but it is on the order of
the sensor bias drift.
There was no apparent scale factor change over the test interval.

See:
http://picasaweb.google.com/DocDough...onsInHydration
for a data set illustrating the stability (at a pH of 6) of the pH of
a sample of flour and water (no starter), the corresponding
calibration measurements,
and the effect of increased sample hydration.
These curves have not been corrected for the sensor offset drift which
can be seen in the top and bottom curves (and also in the flour/water
data).