Dark Beer Bread (75%) - Underproofed?

Hello friends,

I felt like finally trying to bake a bread where most of the liquid comes from dark beer.

Something curious happened that I hope you can help me explain: The fermentation of my "beer dough" progressed quite a bit slower than comparable formulas with water only. Hypothesis: Could the yeast in the beer be competing with the wild yeasts of my (whole rye) leaven - and thus slow down fermentation? 

It's not like I didn't get any fermentation at all, just not an as vigorous one. I had to cut the bulk fermentation short since I needed to go to bed (-> pre-shape -> bench rest -> final shape -> final proof in fridge til next morning).

Now, don't get me wrong: this loaf is definitely edible, outright delicious...but as you can see from the crumb shot, there's lots of room for improvement. What do y'all think?

Warm wishes from Germany,

-Nils

Formula:

• 425g AP (85% of flour total)
• 50g Whole Rye (15% of flour total)
• 50g Whole Rye starter (100% hydration)
• 10 salt
• 335g Guinness dark beer
• 15g water 
• Total hydration: 75%
• liquid temp (after mixed together): 22.5°C / 72.5°F
• Dough temp after mix: 24°C / 75°F
• Bulk @ room temp (24°C / 75°F) for 4:30hrs
• Three folds
• Bench rest for 0:45hrs after pre-shape, than final shape 
• Final proof in the fridge for 9:35hrs (fridge temp is a bit warmer than most people's...around 6°C / 42°F)
• Final final proof ;-) at room temp for 1:10hrs