Sourdough not sour enough
I've started out with sourdoughs and longer fermentation times a couple of months ago and bake without using any extra bakers' yeast. The resulting loaves have excellent texture, crumb, taste (more on that just below). But...they're not sour enough (unless when making a >=50% rye, then it's ok) and I'm looking for some advice to get more 'tang' in them.
Here's what I do:
The starter was built 3 months ago, just a mixture of rye flour and water with a bit of yoghurt added. I let it ferment at room temperature (at that time 30 centigrade, I'm in India) for a total of 3 weeks, discarding/refreshing daily. I taste it regularly and trust me, it's sour. Nowadays I store it in the fridge at 4 centigrade, take it out the morning before baking day and then add about 100 grams of rye flour and 100 grams water. In the course of the day (quite quickly, nowadays with temp about 25 centigrade around 4-6 hours) it gets bubbly, increases its volume etc. In the evening I take out what I put in (200 grams total) and add 150 grams white bread flour and 150 grams water, the remainder goes back in the fridge.
This starter/white bread flour+water mix then sits in a pot outside overnight (night temp about 13 centigrade) and duly increases in volume.
Next morning I add about 500 grams white bread flour, sometimes some seeds/raisins, salt and water to get to about 65% total hydration (to be honest I just make a rough calculation and go by feel, the dough is typically still somewhat sticky but I figure it's best to err on the 'too moist' side).
After kneading this sits in a covered bowl for around 3 hours at 20 centigrade, after which time the volume has doubled. It's then folded, divided and shaped, then gets another 2-3 hours proof. After that I score and bake.
As I said, the resulting loaves have good oven spring and are just about perfect in every way except for the fact that I'd like them to be more tangy (my wife, otoh is quite happy with the way things are going).
From what I've read I might need more lactobacilli and perhaps an even longer fermentation time but that's hard to do as I don't have perfect temperature control and it seems to me that the rise/proof times are already significant. What to do? I could add some yoghurt but I'm guessing that the yeast/lactobacilli ratio automatically reaches some equilibrium. It are probably wild yeasts floating around locally in Delhi, so no idea about what's in there.
Any tips are gratefully accepted!