Can someone explain to me the mechanism by which using old flour in
raised bread baking would lead to a lower volume, denser loaf?

I'm presuming it's because the gluten proteins have oxidized over
time. Is this correct?

If so, then I'm further presuming that removal of the oxygen would
greatly retard any breakdown of the flour, at least so far using it to
bake raised breads are concerned?

This would be for refined white flour - all purpose or bread flour
specifically.

I've been Googling around trying to find the answer to this, but I'm
not putting the search terms together properly it seems because
nothing I find really answers the question of why it happens, just
that it does happen.

Thanks for any light you can shed on this.

......Alan.


--
Curiosity killed the cat -
lack of it is killing mankind.

(A.T. Hagan) wrote in message >...
> Can someone explain to me the mechanism by which using old flour in
> raised bread baking would lead to a lower volume, denser loaf?
>
Aging the flour will lead to maturation and later degradation of
flour.

If the flour is old that it smells musty the mechanism of its
degradation is contributed primarily by the fatty acids present in the
flour fat.These is done by the fat degrading enzymes as well as
oxidation- reduction enzymes such as the lipoxygenase , oxidases and
even protein degrading enyzmes;proteinases.
The flour aging starts the moment ( first stage)its stored and it
will achieve its peak when the reaction of the lipoxgenase with the
unsaturated fatty acids favors the strenghening of the wheat gluten
which is akin to oxidation improvement of the flour. That is the
point that is most beneficial to baking.
Later the second stage the amound of degraded fatty acids reach a
level that free radicals and other reactive decomposition components
will result that gluten strands become taut and less extensive and the
loss of elasticity results.
The gluten can still be formed during the hydration of flour protein
but its quality suffer due to combination of chemical and enzymatic
degradation which is a complex multistep reaction that originates from
the flour fat breakdown.

> I'm presuming it's because the gluten proteins have oxidized over
> time. Is this correct?

That is partly the reason as the tightening of the gluten is akin to
oxidation but has gone beyond the beneficial limit.
Another is at that state it is more sensitive to proteolytic
enzymes .
> If so, then I'm further presuming that removal of the oxygen would
> greatly retard any breakdown of the flour, at least so far using it to
> bake raised breads are concerned?
Removal of oxygen is not the solution, as the dough to be functional
need the sufficient oxygen and if you mixed the dough under high
vacuum the bread quality is inferior or similarly in pure nitrogen
atmosphere meaning that oxygen is required.
Some high speed machines mixes dough under partial vacuum but the
amount of oxidants needed is maximum. Which is the same reasoning that
there really is a need for oxygen in the dough development.
> This would be for refined white flour - all purpose or bread flour
> specifically.
It will be the same with all flours.But the defect is more obvious
with wholemeal and clear flours and less with the refined white flour
which can be classified in the patent category.Even with low ash
flours.
There comes the point that in overaged flour( regardless of the ash
level which )) the chemical reaction that ensues contributes to the
degradation of gluten quality.
The best solution for using overaged flour is to blend it with large
amounts normally aged flour or even freshly milled flour and you can
still obtain satisfactory baking peformance.
That can be confirmed by your baking tests.
Roy

Thanks for the response, Roy. I was hoping someone like you would
respond. This is what I was looking for.

On 13 Nov 2003 20:19:53 -0800, (Roy Basan) wrote:
>Aging the flour will lead to maturation and later degradation of
>flour.
>
>If the flour is old that it smells musty the mechanism of its
>degradation is contributed primarily by the fatty acids present in the
>flour fat.These is done by the fat degrading enzymes as well as
>oxidation- reduction enzymes such as the lipoxygenase , oxidases and
>even protein degrading enyzmes;proteinases.

OK, so if I'm understanding this correctly it's not simply a matter of
oxidation breakdown but also a matter of other enzymes that do not
need the presence of free oxygen in order to function? This seems in
keeping with other aspects of food storage. Oxidative rancidity is
the primary cause affective shelf-life but once that is addressed
there are still other causes that eventually will do the same damage,
just in a larger time frame.

Further, refined white flour suffers the same problems as whole-wheat
flour but at a slower pace because it's fat content is much reduced,
but not completely eliminated.

>Removal of oxygen is not the solution, as the dough to be functional
>need the sufficient oxygen and if you mixed the dough under high
>vacuum the bread quality is inferior or similarly in pure nitrogen
>atmosphere meaning that oxygen is required.
>Some high speed machines mixes dough under partial vacuum but the
>amount of oxidants needed is maximum. Which is the same reasoning that
>there really is a need for oxygen in the dough development.

I'm looking at this as two seperate problems.

The first is how to keep flour in good condition while in storage, or
at least getting a feel for how long it can be stored before it really
begins to go off. White flour specifically - we'd just mill
whole-wheat flour on the spot. This particular flour that I'm dealing
with wasn't supposed to be kept so long but between the time I
purchased and repackaged it and now circumstances changed and we ended
up keeping it a lot longer than originally anticipated. If I had
planned on keeping it this long at the time of purchase I'd have
packed it with some oxygen absorbers which would have given me a
longer shelf-life, but as you seem to be pointing out even in a
no-free-oxygen enviroment other processes will still be ongoing that
puts a definite limit on shelf-life. I am presuming the only thing
that would affect that would be to lower the temperature of the
storage area. Not really an option for me, but others might be able
to do so.

The second would be in the dough itself. I'm thinking that the act of
measuring and mixing the dry ingredients before incorporating the
liquid ingredients would reoxygenate the flour. Is this correct?

>The best solution for using overaged flour is to blend it with large
>amounts normally aged flour or even freshly milled flour and you can
>still obtain satisfactory baking peformance.
>That can be confirmed by your baking tests.
>Roy

This is what we're doing with the old white bread flour. Mixing in
small quantities into the whole wheat flour we're making bread with.
We seem to be getting good rises this way and the bread is pretty
good.

Do you know of any place on the Internet that I could go and read up
on this that doesn't require a cereal chemist's knowledge depth to
understand?

......Alan.

--
Curiosity killed the cat -
lack of it is killing mankind.

(A.T. Hagan) wrote in message >...
>
>
> Do you know of any place on the Internet that I could go and read up
> on this that doesn't require a cereal chemist's knowledge depth to
> understand?
>
> .....Alan.

i am not aware if there is an internet link that could provide you
more information related to your questions.
It is certain that....
You can only get more information from the food science related
library.
Roy