Question about “gummy” crumb streaks?

Question about “gummy” crumb streaks?

Hi all — Overdue for a proper update on recent bread experiments (there have been many this year, from so much time at home!).  But before that, wanted to see if others might be able to help me figure out an occasional problem I see with some sourdough loaves.  Specifically, every 15-20 or so loaves (e.g. infrequent, but not completely one-off), I tend to see a thin layer or layers of only partially cooked/gummy crumb near the bottom of a loaf when I cut it open.  It’s really hard to predict when this will happen until I cut into the loaf, and I’m pretty consistent with my process, cooking time, etc, so I haven’t been able to predict when it will happen.  My current theory is that it is caused by something I’m doing in the shaping process, potentially when I “cinch up” the batard, which can sometimes get a little messy/thick and layered, so I wonder if I’m unintentionally creating some lamination at the bottom of the loaf which causes the gumminess. I’ll attach some photos of a normal/good loaf, one with slight gumminess, and one with egregious example, for reference.

Normal/Target Inside & Out Example:

Slight Gummy Streak Near Bottom Example:


Lots of compression/gumminess at Bottom Example:


Has anyone else experienced this and some up with some solutions? 


Thanks very much in advance!


PS Some additional detail on process:

My baking set up: 3/4″ fibrament baking stone; custom stainless metal steel cover (fits snag around the stone), parchment paper to load the loaves; occasionally some extra water/ice for added steam.  

I generally cook for 20 min with lid on at 500; then 25-30 min lid off at 450; dry out for 6 min with oven off.  

Flours/Hydration: generally a mix of central milling wheat flours (bread and AP) and some fresh milled flour. Hydration in the 75-85% range, depending on the loaf