> The situation has become so serious that in fact
>Australia has been forced to buy German rye flour because there is no longer
>local stock available. The introduction of this new flour manifested a
>disaster for my bakery. The sour made of this German rye has dramatically
>lesser acidity, and it diminishes daily!


If the starter was made properly and fed regulary it will be robust in
time.
I don't believe either that German rye flour produces a different
tanginess than the Australian rye.
Have you tried acclimatizing your Australian rye sour by gradually
using German rye flour but at the same time reducing the Australian rye
flour. until you reach the point that you are using 100% German rye
flour?
In that way whatever microbial flora is present n the German rye flour
can gradually work in harmony with the Australian born culture.
Microbes have the talent for adaptation if they are gradually
acclimatized.
I have that performance variation problem with rye flours but not with
rye meals; why don't you use the meal instead of the flour?
Beside AFAIK most sourdough bakes in Australia used rye meal in natural
sourdough not specific rye flour such as dark or white.
If you are using a whole rye flour you are likely to get consistency
than if you use either dark or light rye flour or meal.
Besides the critters seems to be robust in rye meals than in rye flours
in my experience..
If you don't have the meal try combining the rye flour with whole
wheat meal and it tends to invigorate the rye based culture in my
observation.
I tried this a few times when we were in low supply of rye meal in the
bakery and used wholewheat meal/rye flour blend instead of 100% rye
meal to refresh the culture and it works!
If the flavor appears to be less rye but we added some nondiastatic
rye malt flour to improve the taste.
Another way to increase the tang was to ferment the starter at lower
temperature but at slightly higher hydration but we have to allow the
critters to "fast " or use the available nutrients by just stirring
it up instead of refreshing it with flour and water and allowing it to
stand for 12-24 hours sufficient stirring every 8 hours..
.. Some times we add some wheat germ or diastatic malt to boost
activity of the wheat meal/ rye meal refreshed culture and it often
works in our starter.

BTW,
What kind of gernan rye flour are you using? Does it ihave any specs,
is it fine or coarse, light or dark,?


Roy