Not feeding sourdough starter enough?

My early sourdough loaves looked like that. Now they are less flat and have defined hikes through the crumb rather than a great interlinked cavern. The things that changed:

• my starter became more mature and stable. It lives in the fridge and gets fed 2-3 times a week when I bake. I keep about 250g which gets 100g taken out and replaced for my standard loaf and 180 g on loaf-and-pizza days, plus another 60g at random times when my partner steals some.
• I’ve learned that in my kitchen a sourdough loaf takes a long old time to rise. Sometimes I bake it underproofed because that’s better than not having bread, but really mine needs 24 hours from start to finish.
• I gave up kneading. I read all the methods, watched all the videos... I slammed that dough down 300 times per loaf, kneaded for at least ten minutes, stretched and folded... and never got smooth elastic dough as advertised. Instead I got exhausted sticky dough that was a nightmare to handle and didn’t rise all that well. I’ve come to the conclusion that if dough has enough time it doesn’t require kneading. Now I mix the starter with water, mix in the flour with a rice paddle, mix a bit more about ten minutes later and leave alone for about 22 hours. I might give it a poke if I’m bored, but that’s more for me than the bread.
• Shaping: I used to do a lot of folding/rolling up of dough before I put it in a proving basket for the last hour or two. Now I just kind of punch it down and gather it back up and dump it into a well-floured basket.

I don’t have a current loaf to take a pic to prove my success (just back from Stratford, flying to Stornoway in the morning, had to actually do a discard feed for 1st time this year) but essentially my mantra would be ‘chill and give it time’.

If you are feeding your starter by discarding half of it then adding 40g each of water and flour, then you are feeding it in a 2:1:1 ratio. To see why, do a thought experiment: You start with some amount of starter — let's say 100g. You discard half, leaving 50g. You then add 80g (40+40). That wasn't 2:1:1 (you're 30g short on starter), but you now have 130g. Repeat the process next feeding, half is now 65g, closer to the 80g. Next time it's 145g... each time you feed it, you get closer and closer to that 2:1:1 ratio. The same thing happens if the start was to large to start with — the process you're using will get you to 2:1:1.

Alternatively, another way to do it is to know how much your jar weighs; say it's 150g. Then if you want 160g of starter, half of that is 80g of starter. You put the jar + starter on the scale and discard until you're down to 150+80=230g. Then you add the 40g each flour & water, giving 2:1:1 (and a total starter weight of 160g).

Also, nothing magical about that ratio: for example, I use more flour (45g) than water (30g) when feeding mine — it means it can go longer between feedings (more flour = more food; drier = consumes it slower).

Starter problems normally manifest as either does not rise or not the desired flavor — you're clearly getting rise, from those air pockets. There are a couple things that may cause this:

1. After your first rise (not always doubled with sourdough), partially deflate it. Press it down, even knead it a little. You want to get any big bubbles out. Note that sourdough traditionally has some large holes in it.

2. If you don't get the starter mixed in well, you can have uneven rise, then portions that got more starter will get huge holes.

Other things can contribute too, like overproofing (at least to the going flat — eventually the sourdough bacteria start eating away the gluten), way-too-warm rise temperature, moisture issues (wrong amount of water), etc. I would guess that you might have too much water in your dough (if its going flat) or that you're overproofing it (put it in the oven earlier). Of course, underproofing can also get you uneven bubbles, but I don't see any sign of the crust bursting, though I'm not sure if that's actually a picture of your loaf or not.

I used to use most of my starter with my weekly bake, then progressively double the starter each day from a very small base until my next bake - no discarding means no waste! I usually knew if my starter was well past needing a feed because it would develop an alcoholic smell and a little clear liquid around the edge - alcohol is a byproduct of the fermentation and shows up when almost all the flour has been consumed by the yeast. When left too long without feeding, the yeast will drown in it.

The ratios aren't as important as you think - just try to be reasonably consistent. From memory, a more liquid starter favours lactic bacteria, whereas a 'drier' starter favours another type of bacteria (these bacteria are what put the sour into sourdough - not the yeast itself).

Punch down after the first rise and see if that helps with the distribution of air pockets - though I suspect that has more to do with the mixing in of the starter into the flour. Try cutting the starter up into small cubes (if it is relatively dry) and mixing them in that way to get a better distribution in the dough. Also mix the salt evenly through the flour as it can kill the yeast in concentrated amounts (and check how much salt you are adding).

If you are having problems with the speed of proofing you can put the dough in the fridge (cover in cling form) to slow it down (this also adds to the flavour as it gives the flour more time to break down).

Best of luck!