Help! Dan Leader's Dreikornbrot...

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I have made this recipe many times, as it's my wife's favorite.  However, the last few times I felt the first rising was too fast and as a result the dough didn't  develop enough strength.  The resulting bread was too light and fluffy.  It got better after a day of rest, but it was still too airy for my taste.  So, this time I skipped the instant yeast altogether, thinking a slow first fermentation would help help develop the flavor and strength better.  My starter has always been very vibrant, so I didn't think it would be a problem to depend on it entirely.  Well, after about three hours of not seeing any appreciable difference in the height of the dough, I went ahead and divided it for final proofing.  I have little confidence I'll see much of a rise during this phase either.  Maybe I'll get a little redemption in the oven?  In the past I used what the recipe calls for -- 1 1/2 t. of instant yeast.  It always doubled after a very short time--especially in the hot Atlanta summer.  My kitchen is about 79F, so it's not a temperature problem.  I've never experienced this problem with other recipes that rely only on the sourdough starter.  Are the seeds too much of a burden for the natural yeast to lift?  The recipe is 50% high gluten flour, 50% rye.  Any ideas?

The Gray zone is 50% Rye.  Which is my own label to a dough when I have to decide: Is this a rye or is this a wheat dough?

I think there is a conflict that has to be balanced. The rye likes developed sour and quick proofing, the wheat is a little more flexible but doesn't do too well with quick proofing, the wheat needs the yeast. I would include the yeast but might put in just a little less or find a cooler place to proof.

You have baked it by now, so how did it come out?

Mini O

The bake went ok.  The dough did rise noticeably while proving in the tins.  I guesstimated when it was ready to into the oven.  Probably could've held off a little longer, but my timing was all off with this thing.  There was good oven spring--perhaps too good, since there was a blowout on the top of each loaf.  But the crumb was much tighter, which is what I was trying to accomplish.  Next time I will definitely go back to using instant yeast.  If it rises too fast I'll just degas it and make it start over again.  Thanks for the tip about ryes.  I guess anything 50% needs a little helping hand.