bursting brioche troubleshooting.VAPOUR:
Good morning. After reading your recipe I strongly feel that what contributes to the problem are mainly two items.
1) You have too much sugar in this recipe in relation to the yeast. The yeast quantity should be increased by 50% or a total of 3 1/2 teasp.
2) The baking temp. is way to low. Bare minimum required is 380 degrees I would consider 400 degrees.
Also I might add the following to you. I strongly feel that mixing for 15 minutes is too long. Why, because whereas we know the gluten needs to be developed there comes a time when the gluten strands breakdown from over development & cannot hold the weight of the water any longer water weighs 7 to 8 pounds per gallon that is heavy stuff. The water goes right to the bottom & we now have WHITE TRASH. Cannot save this. We must begin anew. Also use cold ingredients because when you mix for this long your machine generates much heat.... once your dough reaches & exceeds 90 degrees it will begin to emit an odor... You now can throw out this junk. It cannot be saved. I realize you mix longer in this type of recipe, however I would like to see you getting it done sooner like maybe 12 min. max unless you are using a spiral mixer & because they are more efficient you can get it done in 10 min max.
Vapour, Just a little baking science, as you know, flour, yeast, sugar & salt require a ingredient that will encourage them to do their thing. That my friend is WATER. The problem here is that all 4 ingredients are competing for this limited amount of hydration, when this occurs guess what... SUGAR ALWAYS WINS OUT!!!. The yeast is left standing at the post, doing nothing. Thats why we must increase the yeast. I might add I would consider using bread flour or at least bread flour & All purpose combined.
One more thing Vapour, I also believe you are under baking this concoction. Bake till the crust is a mahagony rich color & your temp therm reads 190 degrees. When removing the baking loaf pan out of the oven slam the side on your counter & quickly remove the brioce, if the sides are light in color throw it back in for 5 minutes only to darken the sides. Vapour in slicing this product consider using a electric knife or a serrated bread knife.
Vapour, I hope you will succeed with this recipe. I have modified it somewhat. I will discuss it only if you wish to change this recipe in the future.
Good luck my friend & have a nice day.