I mixed 400gr of flour with 200 of starter, plus 280 ml of water and a bit of salt. I worked it with the slap and fold method and left it overnight. Sadly this morning I woke up to find it only about one third increased in volume. I had a similar experience two days ago, when I baked the loaf but the crumb was dense and the loaf went in the bin. Is there anything that I can do now to rescue the loaf before I bake it? Would it be possible to mix in some regular yeast for example? Thank for your help!
If it’s currently winter for many of us, it’s possible that your dough just needs more time as bread rises slowly when it’s cold.
If that’s the case, you can try moving it to a warmer location
Although there is ‘instant yeast’, which can be mixed straight into dough as you’re making it, I don’t think it’s intended to be added after the dough is made, and further manipulation to get it well distributed may over knead the dough.
You also mentioned that you used ‘brown flour’ in a follow up comment. If this is not the same type of flour as what you have been feeding to your sourdough starter, it may be slower as the yeasts haven’t been specifically bred to consume that flour.