It's alive... but only barely. How can I give my sourdough seed a boost?
Last weekend I created a sourdough seed culture, more or less following the recipe in Peter Reinhart's wonderful Wholegrain Breads book. The only difference I made was that instead of pineapple juice, I used slightly diluted apple juice (apparently the PH of apple juice is around 3, so I diluted it a tad to try and get it closer to pineapple) since I didn't have pineapple on hand.
After a few days (and one feed) I noticed some very small bubbles on the surface, and after stirring these bubbles came back again overnight. I fed the seed again nearly two days ago and am currently on phase 3 as far as I can tell. I haven't started to throw away any of the sponge yet, because it hasn't become very bubbly and I am assuming that because of the temperature of my apartment (16C/60F) the culture is a bit slow. However, I realised today that when feeding the other day, the water I used was filtered and straight from the fridge, so that probably didn't help.
Right now I just transferred my seed culture to a glass dish so that I can see any bubble formation more clearly, and whilst formation is quite rapid now, the bubbles are not sticking around so it's difficult to tell if it's ready.
Is the reason for my culture's sluggish behaviour most likely due to the low air temperature or is another explanation more likely? Any tips for how to increase the activity of the culture? Should I feed it a little more (it's very wet and runny right now), warm it up (I have a radiator that I often use for proofing bread that is suitable), wait or do something else entirely? Any suggestions would be much appreciated.