Starter has become weak and unresponsive.
After pulling out some terrible, barely-risen, tight-crumbed loaves out of my oven the past couple of weeks I had to do some troubleshooting and eventually managed to figure out that my starter is misbehaving. I am not really sure why. The past few months I've kept it at 125% hydration and was feeding it twice a day at a ratio of 1:5:4. Loaves were coming out fine. But the last two weeks it hasn't been working well. Nothing had changed in my feeding schedule or ratio; the only thing is I put it in the fridge for a couple of days when I wasn't baking, but I did refresh it a few times before using it in dough.
I'm wondering if I may have misinterpreted the readiness of my starter all this time, and was using it when it was underripe or overripe. Because it's a high hydration you can't judge by how much it's risen, so I went by smell and bubbles. I think 1:5:4 was possibly not enough as it did develop a little hooch, but I didn't increase the ratio because I'm cheap and wanted to conserve flour (also the breads were coming out fine so it wasn't an issue). Since the problems started (and by that I mean the dough wasn't doubling unless I added some yeast) I decided to up the feed ratio to 1:7.5:6 - the result was the same, still a little hooch, no rising.
At this point I figured I'll do some first aid, reduced hydration to 100% so I can better judge what's happening, and fed it 1:1:1. That was 16:00 yesterday. By 23:00 it had risen by about 30%. This morning it stayed at the same level and there's no indication that it has risen and fallen. Just now I fed it at 1:0.5:0.5 to give it a serious boost and we'll see what happens.
Anyway, the point is, why did this happen? Did the yeast population dilute because of too frequent / infrequent feedings? Did the hydration level / pH levels have anything to do with it? Has the change in temeperature that has happened over the last few weeks messed up my starter somehow? Did the volcanic ash cloud work some voodoo on it? It happened pretty suddenly - one week my breads were fine, the next they were not. Literally nothing changed inbetween except for that short fridge time, and that really shouldn't have such a negative impact on a culture, especially since I did refresh it twice before even using it in bread.
Anyone have any ideas? I know higher hydration cultures ferment quicker which is why I think maybe I was underfeeding all this time, gradually killing the yeast populations. But with regards to the hooch, it was never a large amount at all, just a very thin layer on top, and sometimes it would appear even one hour after feeding - surely not enough time for a culture at room temperature (~19C) to go through a 1:5:4 feed? Or was I misled by this "hooch" (or whatever it was) to think I was underfeeding, and really 1:5:4 was way too much and I was in fact overfeeding to the point where the yeast have been seriously diluted? But if that's the case what is that thin layer of liquid if not a sign of underfeeding? And how can I consistently and reliably judge the ripeness of a liquid culture? "Bubbly" it certainly is, does it have to go all the way to "frothy"?