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Will you share the recipe? I make one but I add a little yeast. I'd love to try a real sourdough brioche. Doesn't sugar usually hasten fermentation rather than inhibit?
I didn't make note of all the amounts yesterday.
Will be making another small batch tonight and increasing the egg/butter amounts. The brioche above is a little on the lean side.
My understanding is that sugar does aid fermentation to a point but too much (above 15% or so?) will effectively retard the fermentation. I'm not sure why this is so... possibly an issue with alcohol/acid levels (fermentation byproducts)? All the various micro organisms in sourdough have different metabolisms so maybe it alters the balance...don't know. Whatever the reason, changing from 25% sugar down to about 12% definitely helped speed the fermentation (which was still slow compared to a lean bread).
Will let you know how things go with today's batch.
The reason why sugar (over about 15%) slows fermentation is that the osmotic pressure of the sugar pulls water away from the yeast cells, slowing the yeast's metabolism. At least that's how it was explained to me. Salt does the same thing. SAF Gold instant yeast ("osmotolerant") is designed to perform better with high-sugar doughs, if you're making a yeasted dough.
Yesterday I was reading a cookbook about the chemical reactions in baking (mainly cakes). It talked about how sugar inhibits the gluten development. Maybe that plays a role as well.
Makes sense to me.
I know that when I add sugar to a fairly stiff dough that it has to be done gradually. The dough starts getting clammy and 'sweats'...kinda icky but it goes back to normal eventually after kneading.
That sounds great. I love enriched sourdoughs, but don't usually do it with butter. I'm lookng foward to seeing your next post and would be quite happy if you were able to get a recipe together.
Increasing the amount of butter and eggs was a success. The result is a richer, more brioche-like brioche!
I'll post the recipe as soon as I get some decent pictures.