What's causing these small holes in the bottom crust of my loaf?

Hi all,

I'm having a curious issue with recent loaves. The bottoms are pock-marked with small holes. Can't figure it out. Here are four pictures of the most recent bake (bottom, top, just after cover removed in the oven and crumb). This is what I'd call a country rye loaf. Any ideas?

Stats below:

Recipe (75% hydration)

AP Flour (Trader Joe's ~11.6%+ protein) 280g

Rye Flour (bulk whole grain dark rye) 80g

Water 260g

Levain: 80g (100% just at peak fermentation)

Salt 8.3g

Method (Dough temp 23-26C (74-78F)

1. Autolyse flour and water - 1 hour

2. Add levain and salt, hand mix ~10 minutes

3. Folds at 30 minutes, 60 minutes, 120 minutes

4. Shape 4 hours after inoculation (1.5x rise at 28.6C (78F))

5. Final proof 18 hours in refrigerator at 6C (43F)

6. Pre-heat oven to 260C (500F)

7. Bake covered 20 minutes with oven OFF

8. Oven temp when the cover was initially removed: 196C (385F)

8. Bake 24 minutes uncovered with heat turned back on to 232C (450F)

Was there any clues when the bottom was up in the basket? Was there condensation? Was the bottom seam completely sealed? Maybe something to do with turning off the oven after it was loaded. Just guessing but it doesn’t seem like it caused any problems because the bread looks good.

Up until taking it out of the oven everything looked perfectly normal. The bottom when in the basket looked smooth as glass and tight, no signs at all. This happened to the last few bakes. The others had the oven on the whole time and there was even a different AP flour used for each. I don't recall whether there was condensation although the bags I use to cover the dough often have some moisture inside after I take them off. Yea, the top and crumb basically look normal.

I’m not sure what would cause that. It almost looks as if fermentation bubbles broke through the crust during final proofing with the seam side up in a banneton. I wonder when you shaped your dough if you had a bit too much flour on the dough? If there was too much flour in spots then the dough may not have sealed as well as it should and that could lead to defects in the crust. There seems to be a bit of flour on the edges of the bottom crust.

Benny

I was thinking the same thing about bubbles but maybe caused in the cast iron pan rather than during proofing. Was wondering if maybe the skin was so thin the slightly bumpy surface of the cast iron caused hot spots that burst bubbles through the skin when the cold dough met the heat of the cast iron. I use that bumpy Lodge cast iron but I also use parchment paper. I don't have a clue. Hoping someone else has run into this and solved it. Yeah, that white stuff on the edges is rice flour from the banneton.